What area of the cortex controls speech?
Broca's area
Broca's area or the Broca area or is a region in the frontal lobe of the dominant hemisphere, usually the left, of the brain with functions linked to speech production.
Conduction aphasia
Recent research has pointed to a different explanation for conduction aphasia, similar to Wernicke's, which is based on newer models suggesting language is facilitated by "cortically based, anatomically distributed, modular networks." Anderson et al. describe an experiment in which electrical stimulation of the left posterior superior temporal cortex in a human subject induced symptoms consistent with conduction aphasia, indicating that a deep brain disconnection is not necessary. While this study does not completely discredit the disconnection hypothesis, but does point to a system in which transmission of spoken language information involves more than just the arcuate fasciculus. Regardless of the role that the arcuate fasciculus plays in the disorder, the cortical component cannot be denied.
Speech perception
Research into the relationship between music and cognition is an emerging field related to the study of speech perception. Originally it was theorized that the neural signals for music were processed in a specialized "module" in the right hemisphere of the brain. Conversely, the neural signals for language were to be processed by a similar "module" in the left hemisphere. However, utilizing technologies such as fMRI machines, research has shown that two regions of the brain traditionally considered exclusively to process speech, Broca's and Wernicke's areas, also become active during musical activities such as listening to a sequence of musical chords. Other studies, such as one performed by Marques et al. in 2006 showed that 8-year-olds who were given six months of musical training showed an increase in both their pitch detection performance and their electrophysiological measures when made to listen to an unknown foreign language.
Language processing in the brain
Although sound perception is primarily ascribed with the AVS, the ADS appears associated with several aspects of speech perception. For instance, in a meta-analysis of fMRI studies (Turkeltaub and Coslett, 2010), in which the auditory perception of phonemes was contrasted with closely matching sounds, and the studies were rated for the required level of attention, the authors concluded that attention to phonemes correlates with strong activation in the pSTG-pSTS region. An intra-cortical recording study in which participants were instructed to identify syllables also correlated the hearing of each syllable with its own activation pattern in the pSTG. The involvement of the ADS in both speech perception and production has been further illuminated in several pioneering functional imaging studies that contrasted speech perception with overt or covert speech production. These studies demonstrated that the pSTS is active only during the perception of speech, whereas area Spt is active during both the perception and production of speech. The authors concluded that the pSTS projects to area Spt, which converts the auditory input into articulatory movements. Similar results have been obtained in a study in which participants' temporal and parietal lobes were electrically stimulated. This study reported that electrically stimulating the pSTG region interferes with sentence comprehension and that stimulation of the IPL interferes with the ability to vocalize the names of objects. The authors also reported that stimulation in area Spt and the inferior IPL induced interference during both object-naming and speech-comprehension tasks. The role of the ADS in speech repetition is also congruent with the results of the other functional imaging studies that have localized activation during speech repetition tasks to ADS regions. An intra-cortical recording study that recorded activity throughout most of the temporal, parietal and frontal lobes also reported activation in the pSTG, Spt, IPL and IFG when speech repetition is contrasted with speech perception. Neuropsychological studies have also found that individuals with speech repetition deficits but preserved auditory comprehension (i.e., conduction aphasia) suffer from circumscribed damage to the Spt-IPL area or damage to the projections that emanate from this area and target the frontal lobe Studies have also reported a transient speech repetition deficit in patients after direct intra-cortical electrical stimulation to this same region. Insight into the purpose of speech repetition in the ADS is provided by longitudinal studies of children that correlated the learning of foreign vocabulary with the ability to repeat nonsense words.
Commissurotomy
Though no effect on behavior was observed after commisurotomy was performed on monkeys, it gave peculiar effects on human perception. Different functions of cognition are predominantly located on one of the hemispheres. For example, Brocas area, crucial for forming sentences, is on most people situated in the left hemisphere ventral to the facial motor cortex. The left hemisphere is referred to as the "talking" hemisphere and the right the "silent". A commisurotomy prevents any sensory input to the silent hemisphere from reaching the talking hemisphere. Since the left visual field is processed in the right hemisphere, a person with a commisurotomy is unable to describe objects to the left, because the "talking" hemisphere has not seen anything. It appears as though the person hadn't seen anything at all, and it doesn't bother him either. It can be demonstrated that stimuli to the right hemisphere for example give emotional response, but because of the severed corpus callosum it cannot be verbalized.
Sam Schmidt Paralysis Foundation
The central nervous system (CNS) controls most functions of the body and mind. It consists of two parts: the brain and the spinal cord. The brain is the center of our thoughts, the interpreter of our external environment, and the origin of control over body movement. Like a central computer, it interprets information from our eyes (sight), ears (sound), nose (smell), tongue (taste) and skin (touch), as well as from internal organs such as the stomach. It controls all voluntary movement, such as speech and walking, and involuntary movement like blinking and breathing. It is the core of our thoughts, perceptions and emotions.
Earl K. Miller
Miller's research aims to understand how the prefrontal cortex, a neural system located in the frontal lobe of the brain, subserves cognitive control. Cognitive or executive control involves the higher-order processing that comes into play when our behavior has to be guided by plans, thoughts, and goals. This sort of behavior contrasts with the one that is primarily driven by external stimuli or by emotion, as well as with behavior that is stereotypical and automatic. Although the prefrontal cortex (PFC) has long been thought to mediate executive functions in the human brain, the mechanisms through which PFC regulates this goal-oriented, purposeful behavior were not clearly understood.
Primary sensory areas
The primary sensory areas are the primary cortical regions of the five sensory systems in the brain (taste, olfaction, touch, hearing and vision). Except for the olfactory system, they receive sensory information from thalamic nerve projections. The term "primary" comes from the fact that these cortical areas are the first level in a hierarchy of sensory information processing in the brain. This should not be confused with the function of the primary motor cortex, which is the "last" site in the cortex for processing motor commands.
Broca's area
Broca's area has been previously associated with a variety of processes, including phonological segmentation, syntactic processing, and unification, all of which involve segmenting and linking different types of linguistic information. Although repeating and reading single words do not engage semantic and syntactic processing, they do require an operation linking phonemic sequences with motor gestures. Findings indicate that this linkage is coordinated by Broca's area through reciprocal interactions with temporal and frontal cortices responsible for phonemic and articulatory representations, respectively, including interactions with motor cortex before the actual act of speech. Based on these unique findings, it has been proposed that Broca's area is not the seat of articulation per se, but rather is a key node in manipulating and forwarding neural information across large-scale cortical networks responsible for key components of speech production.
Cerebrum
The primary sensory areas of the cerebral cortex receive and process visual, auditory, somatosensory, gustatory, and olfactory information. Together with association cortical areas, these brain regions synthesize sensory information into our perceptions of the world.
Language processing in the brain
In the last two decades, significant advances occurred in our understanding of the neural processing of sounds in primates. Initially by recording of neural activity in the auditory cortices of monkeys and later elaborated via histological staining and fMRI scanning studies, 3 auditory fields were identified in the primary auditory cortex, and 9 associative auditory fields were shown to surround them (Figure 1 top left). Anatomical tracing and lesion studies further indicated of a separation between the anterior and posterior auditory fields, with the anterior primary auditory fields (areas R-RT) projecting to the anterior associative auditory fields (areas AL-RTL), and the posterior primary auditory field (area A1) projecting to the posterior associative auditory fields (areas CL-CM). Recently, evidence accumulated that indicates homology between the human and monkey auditory fields. In humans, histological staining studies revealed two separate auditory fields in the primary auditory region of Heschl's gyrus, and by mapping the tonotopic organization of the human primary auditory fields with high resolution fMRI and comparing it to the tonotopic organization of the monkey primary auditory fields, homology was established between the human anterior primary auditory field and monkey area R (denoted in humans as area hR) and the human posterior primary auditory field and the monkey area A1 (denoted in humans as area hA1). Intra-cortical recordings from the human auditory cortex further demonstrated similar patterns of connectivity to the auditory cortex of the monkey. Recording from the surface of the auditory cortex (supra-temporal plane) reported that the anterior Heschl's gyrus (area hR) projects primarily to the middle-anterior superior temporal gyrus (mSTG-aSTG) and the posterior Heschl's gyrus (area hA1) projects primarily to the posterior superior temporal gyrus (pSTG) and the planum temporale (area PT; Figure 1 top right). Consistent with connections from area hR to the aSTG and hA1 to the pSTG is an fMRI study of a patient with impaired sound recognition (auditory agnosia), who was shown with reduced bilateral activation in areas hR and aSTG but with spared activation in the mSTG-pSTG. This connectivity pattern is also corroborated by a study that recorded activation from the lateral surface of the auditory cortex and reported of simultaneous non-overlapping activation clusters in the pSTG and mSTG-aSTG while listening to sounds.
Anatomy of the cerebellum
The cerebellar lateral expansion, or the neocerebellum, may be associated with cognitive functions, and it is anatomically linked with the lateral prefrontal cortex. It shows greatest activity during speech, with a one-sided predominance consistent with a possible linkage (via the thalamus) with the motor speech area.
Motor cortex
In the earliest work on the motor cortex, researchers recognized only one cortical field involved in motor control. Alfred Walter Campbell was the first to suggest that there might be two fields, a "primary" motor cortex and an "intermediate precentral" motor cortex. His reasons were largely based on cytoarchitectonics, or the study of the appearance of the cortex under a microscope. The primary motor cortex contains cells with giant cell bodies known as "Betz cells". These cells were mistakenly thought to be the main outputs from the cortex, sending fibers to the spinal cord. It has since been found that Betz cells account for about 2-3% of the projections from the cortex to the spinal cord, or about 10% of the projections from the primary motor cortex to the spinal cord. The specific function of the Betz cells that distinguishes them from other output cells of the motor cortex remains unknown, but they continue to be used as a marker for the primary motor cortex.
Throat
It works with the mouth, ears and nose, as well as a number of other parts of the body. Its pharynx is connected to the mouth, allowing speech to occur, and food and liquid to pass down the throat. It is joined to the nose by the nasopharynx at the top of the throat, and to ear by its Eustachian tube. The throat's trachea carries inhaled air to the bronchi of the lungs. The esophagus carries food through the throat to the stomach. Adenoids and tonsils help prevent infection and are composed of lymph tissue. The larynx contains vocal cords, the epiglottis (preventing food/liquid inhalation), and an area known as the subglottic larynx—the narrowest section of the upper part of the throat. In the larynx, the vocal cords consist of two membranes that act according to the pressure of the air.
Speech
Paul Broca identified an approximate region of the brain in 1861 which, when damaged in two of his patients, caused severe deficits in speech production, where his patients were unable to speak beyond a few monosyllabic words. This deficit, known as Broca's or expressive aphasia, is characterized by difficulty in speech production where speech is slow and labored, function words are absent, and syntax is severely impaired, as in telegraphic speech. In expressive aphasia, speech comprehension is generally less affected except in the comprehension of grammatically complex sentences. Wernicke's area is named after Carl Wernicke, who in 1874 proposed a connection between damage to the posterior area of the left superior temporal gyrus and aphasia, as he noted that not all aphasic patients had suffered damage to the prefrontal cortex. Damage to Wernicke's area produces Wernicke's or receptive aphasia, which is characterized by relatively normal syntax and prosody but severe impairment in lexical access, resulting in poor comprehension and nonsensical or jargon speech.
Beat deafness
When sound waves reach the ears, the energy they contain is converted into electrical signals, which are sent via the auditory nerves to the brain. Sound processing begins when these electrical signals reach the primary auditory receiving area in the core part of the temporal lobe. Signals then travel to the area surrounding the core, known as the belt area, and are then transmitted to the parabelt area, which is located next to the belt. Simple sounds such as pure tones are able to activate the core area of the brain, but both the belt and parabelt areas are activated by only complex sounds, such as those found in speech and music. The auditory cortex in the left hemisphere of the brain is responsible for processing beat and rhythm in music. The right auditory cortex is primarily used in distinguishing between different harmonics, which are simple pure tones that combine to create complex tones.
Auditory system
Perception of sound is associated with the left posterior superior temporal gyrus (STG). The superior temporal gyrus contains several important structures of the brain, including Brodmann areas 41 and 42, marking the location of the primary auditory cortex, the cortical region responsible for the sensation of basic characteristics of sound such as pitch and rhythm. We know from research in nonhuman primates that the primary auditory cortex can probably be divided further into functionally differentiable subregions.
Impulsivity
Although the precise neural mechanisms underlying disorders of impulse control are not fully known, the prefrontal cortex (PFC) is the brain region most ubiquitously implicated in impulsivity. Damage to the prefrontal cortex has been associated with difficulties preparing to act, switching between response alternatives, and inhibiting inappropriate responses. Recent research has uncovered additional regions of interest, as well as highlighted particular subregions of the PFC, that can be tied to performance in specific behavioral tasks.
Split-brain
The two hemispheres of the cerebral cortex are linked by the corpus callosum, through which they communicate and coordinate actions and decisions. Communication and coordination between the two hemispheres is essential because each hemisphere has some separate functions. The right hemisphere of the cortex excels at nonverbal and spatial tasks, whereas the left hemisphere is more dominant in verbal tasks, such as speaking and writing. The right hemisphere controls the primary sensory functions of the left side of the body. In a cognitive sense the right hemisphere is responsible for recognition of objects and timing, and in an emotional sense it is responsible for empathy, humour and depression. On the other hand, the left hemisphere controls the primary sensory functions of the right side of the body and is responsible for scientific and maths skills, and logic. The extent of specialised brain function by an area remains under investigation. It is claimed that the difference between the two hemispheres is that the left hemisphere is "analytic" or "logical" while the right hemisphere is "holistic" or "intuitive". Many simple tasks, especially comprehension of inputs, require functions that are specific to both the right and left hemispheres and together form a one direction systematised way of creating an output through the communication and coordination that occurs between hemispheres.
Language processing in the brain
Throughout the 20th century the dominant model for language processing in the brain was the Geschwind-Lichteim-Wernicke model, which is based primarily on the analysis of brain damaged patients. However, due to improvements in intra-cortical electrophysiological recordings of monkey and human brains, as well non-invasive techniques such as fMRI, PET, MEG and EEG, a dual auditory pathway has been revealed. In accordance with this model, there are two pathways that connect the auditory cortex to the frontal lobe, each pathway accounting for different linguistic roles. The auditory ventral stream pathway is responsible for sound recognition, and is accordingly known as the auditory 'what' pathway. The auditory dorsal stream in both humans and non-human primates is responsible for sound localization, and is accordingly known as the auditory 'where' pathway. In humans, this pathway (especially in the left hemisphere) is also responsible for speech production, speech repetition, lip-reading, and phonological working memory and long-term memory. In accordance with the 'from where to what' model of language evolution. the reason the ADS is characterized with such a broad range of functions is that each indicates a different stage in language evolution.
Cerebral cortex
The cerebral cortex is connected to various subcortical structures such as the thalamus and the basal ganglia, sending information to them along efferent connections and receiving information from them via afferent connections. Most sensory information is routed to the cerebral cortex via the thalamus. Olfactory information, however, passes through the olfactory bulb to the olfactory cortex (piriform cortex). The majority of connections are from one area of the cortex to another, rather than from subcortical areas; Braitenberg and Schüz (1998) claim that in primary sensory areas, at the cortical level where the input fibres terminate, up to 20% of the synapses are supplied by extracortical afferents but that in other areas and other layers the percentage is likely to be much lower.
Cognitive neuropsychology
In 1861 Paul Broca, reported a post mortem study of an aphasic patient who was speechless apart from a single nonsense word: "Tan". Broca showed that an area of the left frontal lobe was damaged. As Tan was unable to produce speech but could still understand it, Broca argued that this area might be specialised for speech production and that language skills might be localized to this cortical area. Broca did a similar study on another patient, Lelong, a few weeks later. Lelong, like Tan, could understand speech but could only repeat the same 5 words. After examining his brain, Broca noticed that Lelong had a lesion in approximately the same area as his patient Tan. He also noticed that in the more than 25 patients he examined with aphasia, they all had lesions to the left frontal lobe but there was no damage to the right hemisphere of the brain. From this he concluded that the function of speech was probably localized in the inferior frontal gyrus of the left hemisphere of the brain, an area now known as Broca's area.
Lateralization of brain function
Broca's area and Wernicke's area, two areas associated with the production of speech, are located in the left cerebral hemisphere for about 95% of right-handers, but about 70% of left-handers.
Aggression
The broad area of the cortex known as the prefrontal cortex (PFC) is crucial for self-control and inhibition of impulses, including inhibition of aggression and emotions. Reduced activity of the prefrontal cortex, in particular its medial and orbitofrontal portions, has been associated with violent/antisocial aggression. In addition, reduced response inhibition has been found in violent offenders, compared to non-violent offenders.
Auditory imagery
During auditory verbal imagery, the inferior frontal cortex and the insula were activated as well as the supplementary motor area, left superior temporal/inferior parietal region, the right posterior cerebellar cortex, the left precentral, and superior temporal gyri. Other areas of the brain have been activated during auditory imagery however there hasn’t been an encoding process attributed to it yet such as frontopolar areas, and the subcallosal gyrus.
Corticobulbar tract
The corticobulbar tract is composed of the upper motor neurons of the cranial nerves. The muscles of the face, head and neck are controlled by the corticobulbar system, which terminates on motor neurons within brainstem motor nuclei. This is in contrast to the corticospinal tract in which the cerebral cortex connects to spinal motor neurons, and thereby controls movement of the torso, upper and lower limbs. Fibers that end in the sensory nuclei of the brainstem are thought to enhance or inhibit sensory transmission across various sensory nuclei. This allows for the selective attention or inattention towards various stimuli.
Laterality
Laterality of motor and sensory control has been the subject of a recent intense study and review. It turns out that the hemisphere of speech is the hemisphere of action in general and that the command hemisphere is located either in the right or the left hemisphere (never in both). Around eighty percent of people are left hemispheric for speech and the remainder are right hemispheric: ninety percent of right-handers are left hemispheric for speech, but only fifty percent of left-handers are right hemispheric for speech (the remainder are left hemispheric). The reaction time of the neurally dominant side of the body (the side opposite to the major hemisphere or the command center, as just defined) is shorter than that of the opposite side by an interval equal to the interhemispheric transfer time. Thus, one in five persons has a handedness that is the opposite for which they are wired (per laterality of command center or brainedness, as determined by reaction time study mentioned above).Cerebral dominance or specialization has been studied in relation to a variety of human functions. With speech in particular, many studies have been used as evidence that it is generally localized in the left hemisphere. Research comparing the effects of lesions in the two hemispheres, split-brain patients, and perceptual asymmetries have aided in the knowledge of speech lateralization. In one particular study, the left hemisphere’s sensitivity to differences in rapidly changing sound cues was noted (Annett, 1991). This has real world implication, since very fine acoustic discriminations are needed to comprehend and produce speech signals. In an electrical stimulation demonstration performed by Ojemann and Mateer (1979), the exposed cortex was mapped revealing the same cortical sites were activated in phoneme discrimination and mouth movement sequences (Annett, 1991).
Cerebral cortex
The association areas are the parts of the cerebral cortex that do not belong to the primary regions. They function to produce a meaningful perceptual experience of the world, enable us to interact effectively, and support abstract thinking and language. The parietal, temporal, and occipital lobes - all located in the posterior part of the cortex - integrate sensory information and information stored in memory. The frontal lobe or prefrontal association complex is involved in planning actions and movement, as well as abstract thought. Globally, the association areas are organized as distributed networks. Each network connects areas distributed across widely spaced regions of the cortex. Distinct networks are positioned adjacent to one another yielding a complex series of interwoven networks. The specific organization of the association networks is debated with evidence for interactions, hierarchical relationships, and competition between networks. 
In humans, association networks are particularly important to language function. In the past it was theorized that language abilities are localized in Broca's area in areas of the left inferior frontal gyrus, BA44 and BA45, for language expression and in Wernicke's area BA22, for language reception. However, the processes of language expression and reception have been shown to occur in areas other than just those structures around the lateral sulcus, including the frontal lobe, basal ganglia, cerebellum, and pons.
Sensory cortex
The sensory cortex can refer informally to the primary somatosensory cortex, or it can be used as a term for the primary and secondary cortices of the different senses (two cortices each, on left and right hemisphere): the visual cortex on the occipital lobes, the auditory cortex on the temporal lobes, the primary olfactory cortex on the uncus of the piriform region of the temporal lobes, the gustatory cortex on the insular lobe (also referred to as the insular cortex), and the primary somatosensory cortex on the anterior parietal lobes. Just posterior to the primary somatosensory cortex lies the somatosensory association cortex, which integrates sensory information from the primary somatosensory cortex (temperature, pressure, etc.) to construct an understanding of the object being felt. Inferior to the frontal lobes are found the olfactory bulbs, which receive sensory input from the olfactory nerves and route those signals throughout the brain. Not all olfactory information is routed to the olfactory cortex. Some neural fibers are routed directly to limbic structures, while others are routed to the supraorbital region of the frontal lobe. Such a direct limbic connection makes the olfactory sense unique.
Perirhinal cortex
The Perirhinal cortex is a cortical region in the medial temporal lobe that is made up of Brodmann areas 35 and 36. It receives highly processed sensory information from all sensory regions, and is generally accepted to be an important region for memory. It is bordered caudally by postrhinal cortex or parahippocampal cortex (homologous regions in rodents and primates, respectively) and ventrally and medially by entorhinal cortex.
Sandra Witelson
Witelson published a paper in 1976 detailing how the brains of six-year-old boys use a single hemisphere when reading, whereas girls use both sides of the brain while performing the same task. She also found that female brains had a thicker corpus callosum - the bridge between hemispheres - and that the thickness was in the region of linguistic skills. A different study showed that women have more brain cells than men in the language region. She also noted that the amygdala, which becomes more active in times of negative stress, signals more strongly to areas controlling motor skills in men, whereas in women, it signals more to the hypothalamus, which controls internal functions such as breathing and heart rate.
Temporal dynamics of music and language
Some of the above-mentioned areas have been shown to be active in both music and language processing through PET and fMRI studies. These areas include the primary motor cortex, the Brocas area, the cerebellum, and the primary auditory cortices.
Motor cortex
The motor cortex is the region of the cerebral cortex involved in the planning, control, and execution of voluntary movements.
Classically the motor cortex is an area of the frontal lobe located in the posterior precentral gyrus immediately anterior to the central sulcus.
Working memory
Brain imaging has also revealed that working memory functions are not limited to the PFC. A review of numerous studies shows areas of activation during working memory tasks scattered over a large part of the cortex. There is a tendency for spatial tasks to recruit more right-hemisphere areas, and for verbal and object working memory to recruit more left-hemisphere areas. The activation during verbal working memory tasks can be broken down into one component reflecting maintenance, in the left posterior parietal cortex, and a component reflecting subvocal rehearsal, in the left frontal cortex (Broca's area, known to be involved in speech production).
Speech production
The physical structure of the human nose, throat, and vocal cords allows for the productions of many unique sounds, these areas can be further broken down into places of articulation. Different sounds are produced in different areas, and with different muscles and breathing techniques. Our ability to utilize these skills to create the various sounds needed to communicate effectively is essential to our speech production. Speech is a psychomotor activity. Speech between two people is a conversation - they can be casual, formal, factual, or transactional, and the language structure/ narrative genre employed differs depending upon the context. Affect is a significant factor that controls speech, manifestations that disrupt memory in language use due to affect include feelings of tension, states of apprehension, as well as physical signs like nausea. Language level manifestations that affect brings could be observed with the speaker's hesitations, repetitions, false starts, incompletion, syntactic blends, etc. Difficulties in manner of articulation can contribute to speech difficulties and impediments. It is suggested that infants are capable of making the entire spectrum of possible vowel and consonant sounds. IPA has created a system for understanding and categorizing all possible speech sounds, which includes information about the way in which the sound is produced, and where the sounds is produced. This is extremely useful in the understanding of speech production because speech can be transcribed based on sounds rather than spelling, which may be misleading depending on the language being spoken. Average speaking rates are in the 120 to 150 words per minute (wpm) range, and same is the recommended guidelines for recording audiobooks. As people grow accustomed to a particular language they are prone to lose not only the ability to produce certain speech sounds, but also to distinguish between these sounds.
Broca's area
"Hand/mouth goal-directed action representations" is another way of saying "gestural communication", "gestural language", or "communication through body language". The recent finding that Broca's area is active when people are observing others engaged in meaningful action is evidence in support of this idea. It was hypothesized that a precursor to the modern Broca's area was involved in translating gestures into abstract ideas by interpreting the movements of others as meaningful action with an intelligent purpose. It is argued that over time the ability to predict the intended outcome and purpose of a set of movements eventually gave this area the capability to deal with truly abstract ideas, and therefore (eventually) became capable of associating sounds (words) with abstract meanings. The observation that frontal language areas are activated when people observe Hand Shadows is further evidence that human language may have evolved from existing neural substrates that evolved for the purpose of gesture recognition. The study, therefore, claims that Broca's area is the "motor center for speech", which assembles and decodes speech sounds in the same way it interprets body language and gestures. Consistent with this idea is that the neural substrate that regulated motor control in the common ancestor of apes and humans was most likely modified to enhance cognitive and linguistic ability. Studies of speakers of American Sign Language and English suggest that the human brain recruited systems that had evolved to perform more basic functions much earlier; these various brain circuits, according to the authors, were tapped to work together in creating language.
Paraphasia
Two areas of the brain, Broca’s area and Wernicke’s area, are responsible for various disruptions in speech when damaged. Each is defined by their distinct characteristics. Broca’s aphasia is characterized by non-fluent or telegraphic-type speech - where articles, conjunctions, prepositions, auxiliary verbs, pronouns and morphological inflections (plurals, past tense) are omitted. The word substitutions are infrequent and distortion of consonants and simplification of consonant clusters is frequent. Content words such as nouns, verbs and adjectives may be preserved. Subjects of this aphasia are aware of their errors in speech. Damage to the Broca’s area does not affect comprehension of speech.
Cortex (anatomy)
In anatomy and zoology, the cortex (Latin for bark, rind, shell or husk) is the outermost (or superficial) layer of an organ. Organs with well-defined cortical layers include kidneys, adrenal glands, ovaries, the thymus, and portions of the brain, including the cerebral cortex, the best-known of all cortices.The cerebral cortex is typically described as comprising three parts: the sensory, motor, and association areas. These sensory areas receive and process information from the senses. The senses of vision, audition, and touch are served by the primary visual cortex, primary auditory cortex and primary somatosensory cortex. The cerebellar cortex is the thin gray surface layer of the cerebellum, consisting of an outer molecular layer or stratum moleculare, a single layer of Purkinje cells (the ganglionic layer), and an inner granular layer or stratum granulosum. The cortex is the outer surface of the cerebrum and is composed of gray matter.
Cortical stimulation mapping
Language mapping is normally done in the left hemisphere of the brain where most language areas are located, such as Broca's and Wernicke's areas. Cortical stimulation mapping has also identified a language area in the basal temporal cortex that was previously unknown.
Temporal lobe
The temporal lobe communicates with the hippocampus and plays a key role in the formation of explicit long-term memory modulated by the amygdala.
The temporal lobe holds the primary auditory cortex, which is important for the processing of semantics in both speech and vision in humans. Wernicke's area, which spans the region between temporal and parietal lobes, plays a key role (in tandem with Broca's area in the frontal lobe) in speech comprehension. The functions of the left temporal lobe are not limited to low-level perception but extend to comprehension, naming, and verbal memory.
Gesture
Gestures are processed in the same areas of the brain as speech and sign language such as the left inferior frontal gyrus (Broca's area) and the posterior middle temporal gyrus, posterior superior temporal sulcus and superior temporal gyrus (Wernicke's area). It has been suggested that these parts of the brain originally supported the pairing of gesture and meaning and then were adapted in human evolution "for the comparable pairing of sound and meaning as voluntary control over the vocal apparatus was established and spoken language evolved". As a result, it underlies both symbolic gesture and spoken language in the present human brain. Their common neurological basis also supports the idea that symbolic gesture and spoken language are two parts of a single fundamental semiotic system that underlies human discourse.
The linkage of hand and body gestures in conjunction with speech is further revealed by the nature of gesture use in blind individuals during conversation. This phenomenon uncovers a function of gesture that goes beyond portraying communicative content of language and extends David McNeill's view of the gesture-speech system. This suggests that gesture and speech work tightly together, and a disruption of one (speech or gesture) will cause a problem in the other. Studies have found strong evidence that speech and gesture are innately linked in the brain and work in an efficiently wired and choreographed system. McNeill's view of this linkage in the brain is just one of three currently up for debate; the others declaring gesture to be a "support system" of spoken language or a physical mechanism for lexical retrieval.
Neurocomputational speech processing
Each neuron (model cell, artificial neuron) within the speech sound map can be activated and subsequently activates a forward motor command towards the motor map, called articulatory velocity and position map. The activated neural representation on the level of that motor map determines the articulation of a speech unit, i.e. controls all articulators (lips, tongue, velum, glottis) during the time interval for producing that speech unit. Forward control also involves subcortical structures like the cerebellum, not modelled in detail here.
Adolescence
The first areas of the brain to be pruned are those involving primary functions, such as motor and sensory areas. The areas of the brain involved in more complex processes lose matter later in development. These include the lateral and prefrontal cortices, among other regions. Some of the most developmentally significant changes in the brain occur in the prefrontal cortex, which is involved in decision making and cognitive control, as well as other higher cognitive functions. During adolescence, myelination and synaptic pruning in the prefrontal cortex increases, improving the efficiency of information processing, and neural connections between the prefrontal cortex and other regions of the brain are strengthened. This leads to better evaluation of risks and rewards, as well as improved control over impulses. Specifically, developments in the dorsolateral prefrontal cortex are important for controlling impulses and planning ahead, while development in the ventromedial prefrontal cortex is important for decision making. Changes in the orbitofrontal cortex are important for evaluating rewards and risks.
Language acquisition
During early infancy, language processing seems to occur over many areas in the brain. However, over time, it gradually becomes concentrated into two areas – Broca's area and Wernicke's area. Broca's area is in the left frontal cortex and is primarily involved in the production of the patterns in vocal and sign language. Wernicke's area is in the left temporal cortex and is primarily involved in language comprehension. The specialization of these language centers is so extensive that damage to them results in a critical condition known as aphasia.
Neocortex
The neocortex is derived embryonically from the dorsal telencephalon, which is the rostral part of the forebrain. The neocortex is divided, into regions demarcated by the cranial sutures in the skull above, into frontal, parietal, occipital, and temporal lobes, which perform different functions. For example, the occipital lobe contains the primary visual cortex, and the temporal lobe contains the primary auditory cortex. Further subdivisions or areas of neocortex are responsible for more specific cognitive processes. In humans, the frontal lobe contains areas devoted to abilities that are enhanced in or unique to our species, such as complex language processing localized to the ventrolateral prefrontal cortex (Broca's area). In humans and other primates, social and emotional processing is localized to the orbitofrontal cortex. ("See Cerebral cortex and Cerebrum.")
Dual systems model
The cognitive control system refers to the lateral prefrontal, lateral parietal, and anterior cingulate cortices. The most commonly investigated region is the prefrontal cortex which undergoes substantial development throughout adolescence. The development of the prefrontal cortex has been implicated in the ability to regulate behavior and engage in inhibitory control.
Speech production
The motor control for speech production in right handed people depends mostly upon areas in the left cerebral hemisphere. These areas include the bilateral supplementary motor area, the left posterior inferior frontal gyrus, the left insula, the left primary motor cortex and temporal cortex. There are also subcortical areas involved such as the basal ganglia and cerebellum. The cerebellum aids the sequencing of speech syllables into fast, smooth and rhythmically organized words and longer utterances.
Auditory system
From the primary auditory cortex emerge two separate pathways: the auditory ventral stream and auditory dorsal stream. The auditory ventral stream includes the anterior superior temporal gyrus, anterior superior temporal sulcus, middle temporal gyrus and temporal pole. Neurons in these areas are responsible for sound recognition, and extraction of meaning from sentences. The auditory dorsal stream includes the posterior superior temporal gyrus and sulcus, inferior parietal lobule and intra-parietal sulcus. Both pathways project in humans to the inferior frontal gyrus. The most established role of the auditory dorsal stream in primates is sound localization. In humans, the auditory dorsal stream in the left hemisphere is also responsible for speech repetition and articulation, phonological long-term encoding of word names, and verbal working memory.
Cerebral cortex
The map of functional cortical areas, which include primary motor and visual cortex, originates from a 'protomap', which is regulated by molecular signals such as fibroblast growth factor FGF8 early in embryonic development. These signals regulate the size, shape, and position of cortical areas on the surface of the cortical primordium, in part by regulating gradients of transcription factor expression, through a process called cortical patterning. Examples of such transcription factors include the genes EMX2 and PAX6. Together, both transcription factors form an opposing gradient of expression. Pax6 is highly expressed at the rostral lateral pole, while Emx2 is highly expressed in the caudomedial pole. The establishment of this gradient is important for proper development. For example, mutations in Pax6 can cause expression levels of Emx2 to expand out of its normal expression domain, which would ultimately lead to an expansion of the areas normally derived from the caudal medial cortex, such as the visual cortex. On the contrary, if mutations in Emx2 occur, it can cause the Pax6-expressing domain to expand and result in the frontal and motor cortical regions enlarging. Therefore, researchers believe that similar gradients and signaling centers next to the cortex could contribute to the regional expression of these transcription factors.
Two very well studied patterning signals for the cortex include FGF and retinoic acid. If FGFs are misexpressed in different areas of the developing cortex, cortical patterning is disrupted. Specifically, when Fgf8 is increased in the anterior pole, Emx2 is downregulated and a caudal shift in the cortical region occurs. This ultimately causes an expansion of the rostral regions. Therefore, Fgf8 and other FGFs play a role in the regulation of expression of Emx2 and Pax6 and represent how the cerebral cortex can become specialized for different functions.
Language processing in the brain
Downstream to the auditory cortex, anatomical tracing studies in monkeys delineated projections from the anterior associative auditory fields (areas AL-RTL) to ventral prefrontal and premotor cortices in the inferior frontal gyrus (IFG) and amygdala. Cortical recording and functional imaging studies in macaque monkeys further elaborated on this processing stream by showing that acoustic information flows from the anterior auditory cortex to the temporal pole (TP) and then to the IFG. This pathway is commonly referred to as the auditory ventral stream (AVS; Figure 1, bottom left-red arrows). In contrast to the anterior auditory fields, tracing studies reported that the posterior auditory fields (areas CL-CM) project primarily to dorsolateral prefrontal and premotor cortices (although some projections do terminate in the IFG. Cortical recordings and anatomical tracing studies in monkeys further provided evidence that this processing stream flows from the posterior auditory fields to the frontal lobe via a relay station in the intra-parietal sulcus (IPS). This pathway is commonly referred to as the auditory dorsal stream (ADS; Figure 1, bottom left-blue arrows). Comparing the white matter pathways involved in communication in humans and monkeys with diffusion tensor imaging techniques indicates of similar connections of the AVS and ADS in the two species (Monkey, Human). In humans, the pSTG was shown to project to the parietal lobe (sylvian parietal-temporal junction- inferior parietal lobule; Spt-IPL), and from there to dorsolateral prefrontal and premotor cortices (Figure 1, bottom right-blue arrows), and the aSTG was shown to project to the anterior temporal lobe (middle temporal gyrus-temporal pole; MTG-TP) and from there to the IFG (Figure 1 bottom right-red arrows).
Neuroscience of multilingualism
Work in the field of cognitive neuroscience has located classical language areas within the perislyvian cortex of the left hemisphere. This area is crucial for the representation of language, but other areas in the brain are shown to be active in this function as well. Language-related activation occurs in the middle and inferior temporal gyri, the temporal pole, the fusiform gyri, the lingula, in the middle prefrontal areas (i.e. dorsolateral prefrontal cortex), and in the insula. There also appears to be activation in the right hemisphere during most language tasks.
Cerebral cortex
The cerebral cortex is the outer layer of neural tissue of the cerebrum of the brain, in humans and other mammals. It is separated into two cortices, by the longitudinal fissure that divides the cerebrum into the left and right cerebral hemispheres. The two hemispheres are joined beneath the cortex by the corpus callosum. The cerebral cortex is the largest site of neural integration in the central nervous system. It plays a key role in memory, attention, perception, awareness, thought, language, and consciousness.
Neurocomputational speech processing
The speech sound map - assumed to be located in the inferior and posterior portion of Broca's area (left frontal operculum) - represents (phonologically specified) language-specific speech units (sounds, syllables, words, short phrases). Each speech unit (mainly syllables; e.g. the syllable and word "palm" /pam/, the syllables /pa/, /ta/, /ka/, ...) is represented by a specific model cell within the speech sound map (i.e. punctual neural representations, see above). Each model cell (see artificial neuron) corresponds to a small population of neurons which are located at close range and which fire together.
Brodmann area 45
A strong correlation has been found between speech-language and the anatomically asymmetric pars triangularis. Foundas, et al. showed that language function can be localized to one region of the brain, as Paul Broca had done before them, but they also supported the idea that one side of the brain is more involved with language than the other. The human brain has two hemispheres, and each one looks similar to the other; that is, it looks like one hemisphere is a mirror image of the other. However, Foundas, et al. found that the pars triangularis in Broca's area is actually larger than the same region in the right side of the brain. This "leftward asymmetry" corresponded both in form and function, which means that the part of the brain that is active during language processing is larger. In almost all the test subjects, this was the left side. In fact, the only subject tested that had right-hemispheric language dominance was found to have a rightward asymmetry of the pars triangularis.
Bilingual interactive activation plus
The neural correlates of the task/ decision subsystem consist of multiple components that map onto different areas of prefrontal cortex responsible for executing control functions. For example, the general executive functions of language switching have been found to activate the anterior cingulate cortex and dorsolateral prefrontal cortex areas.,
Drew Westen
Specifically, when Republican test subjects were shown self-contradictory quotes by George W. Bush and when Democratic test subjects were shown self-contradictory quotes by John Kerry, both groups tended to explain away the apparent contradictions in a manner biased to favor their candidate of choice. Similarly, areas of the brain responsible for reasoning (presumably the prefrontal cortex ) did not respond during these conclusions while areas of the brain controlling emotions (presumably the amygdala and/or cingulate gyrus) showed increased activity as compared to the subject's responses to politically neutral statements associated with politically neutral people (such as Tom Hanks).
Neuronal recycling hypothesis
As was stated in the neuronal recycling hypothesis, brain circuits bias what we are able to learn. One bias identified involves the preference of central versus peripheral images at different points along the cerebral cortex. It was observed that in all individuals, the visual word form area fell on the region of the cortex with a massive preference for fine-grained, central images. This area is most suitable to accommodate reading ability, due to the high degree of visual precision necessary to perform this function effectively. Another cortical bias relevant to reading comes from the lateralization of cerebral hemispheres. Reading consistently activates the left hemisphere, which is associated with language abilities and discriminating between small shapes, showing a clear bias towards reading functions. There is a preadaptation of the inferior temporal cortex that we use when learning to read. It is the area activated during invariant object recognition, and it's sufficient plasticity allows it to accommodate the new shapes and symbols necessary for reading.
Dyslexia research
Brain activation studies using PET to study language have found that people with dyslexia have a deficit in parts of the left hemisphere of the brain involved in reading, which includes the inferior frontal gyrus, inferior parietal lobule, and middle and ventral temporal cortex. A neural basis for the visual lexicon and for auditory verbal short term memory components have been proposed. Wernicke's and Broca's areas are being recast in terms of localized components of phonological input and output. Some classical regions, such as the arcuate fasciculus, are having their "classical" roles questioned, while other regions, such as the basal temporal language zone, are growing progressively in terms of their recognized importance.
Albert Einstein's brain
Scientists are currently interested in the possibility that physical differences in brain structure could determine different abilities. One part of the operculum called Broca's area plays an important role in speech production. To compensate, the inferior parietal lobe was 15 percent wider than normal. The inferior parietal region is responsible for mathematical thought, visuospatial cognition, and imagery of movement.
Vocal learning
Humans seem to have analogous anterior and posterior vocal pathways which are implicated in speech production and learning. Parallel to the avian posterior vocal pathway mentioned above is the motor cortico-brainstem pathway. Within this pathway, the face motor cortex projects to the nucleus ambiguous of the medulla, which then projects to the muscles of the larynx. Humans also have a vocal pathway that is analogous to the avian anterior pathway. This pathway is a cortico-basal ganglia-thalamic-cortico loop which begins at a strip of the premotor cortex, called the cortical strip, which is responsible for speech learning and syntax production. The cortical strip includes spans across five brain regions: the anterior insula, Broca’s area, the anterior dorsal lateral prefrontal cortex, the anterior pre-supplementary motor area, and the anterior cingulate cortex. This cortical strip has projections to the anterior striatum which projects to the globus pallidus to the anterior dorsal thalamus back to the cortical strip. All of these regions are also involved in syntax and speech learning.
Exhalation
The neurological pathway of voluntary exhalation is complex and not fully understood. However, a few basics are known. The motor cortex within the cerebral cortex of the brain is known to control voluntary respiration because the motor cortex controls voluntary muscle movement. This is referred to as the corticospinal pathway or ascending respiratory pathway. The pathway of the electrical signal starts in the motor cortex, goes to the spinal cord, and then to the respiratory muscles. The spinal neurons connect directly to the respiratory muscles. Initiation of voluntary contraction and relaxation of the internal and external internal costals has been shown to take place in the superior portion of the primary motor cortex. Posterior to the location of thoracic control (within the superior portion of the primary motor cortex) is the center for diaphragm control. Studies indicate that there are numerous other sites within the brain that may be associated with voluntary expiration. The inferior portion of the primary motor cortex may be involved, specifically, in controlled exhalation. Activity has also been seen within the supplementary motor area and the premotor cortex during voluntary respiration. This is most likely due to the focus and mental preparation of the voluntary muscular movement.
Tonotopy
Tonotopy in the auditory system begins at the cochlea, the small snail-like structure in the inner ear that sends information about sound to the brain. Different regions of the basilar membrane in the organ of Corti, the sound-sensitive portion of the cochlea, vibrate at different sinusoidal frequencies due to variations in thickness and width along the length of the membrane. Nerves that transmit information from different regions of the basilar membrane therefore encode frequency tonotopically. This tonotopy then projects through the vestibulocochlear nerve and associated midbrain structures to the primary auditory cortex via the auditory radiation pathway.
Throughout this radiation, organization is linear with relation to placement on the organ of Corti, in accordance to the best frequency response (that is, the frequency at which that neuron is most sensitive) of each neuron. However, binaural fusion in the superior olivary complex onward adds significant amounts of information encoded in the signal strength of each ganglion. Thus, the number of tonotopic maps varies between species and the degree of binaural synthesis and separation of sound intensities; in humans, six tonotopic maps have been identified in the primary auditory cortex. their anatomical locations along the auditory cortex.
Neurobiological origins of language
In order to speak, the breathing system must be voluntarily repurposed to produce vocal sounds, which allows the breathing mechanisms to be temporarily deactivated in favor of song or speech production. The human vocal tract has evolved to be more suited to speaking, with a lower larynx, 90° turn in the windpipe, and large, round tongue. Motor neurons in birds and humans bypass the unconscious systems in the brainstem to give direct control of the larynx to the brain.
Brodmann area
Many of those brain areas defined by Brodmann have their own complex internal structures. In a number of cases, brain areas are organized into topographic maps, where adjoining bits of the cortex correspond to adjoining parts of the body, or of some more abstract entity. A simple example of this type of correspondence is the primary motor cortex, a strip of tissue running along the anterior edge of the central sulcus. Motor areas innervating each part of the body arise from a distinct zone, with neighboring body parts represented by neighboring zones. Electrical stimulation of the cortex at any point causes a muscle-contraction in the represented body part. This "somatotopic" representation is not evenly distributed, however. The head, for example, is represented by a region about three times as large as the zone for the entire back and trunk. The size of any zone correlates to the precision of motor control and sensory discrimination possible. The areas for the lips, fingers, and tongue are particularly large, considering the proportional size of their represented body parts.
Kinesthetic learning
The cerebral cortex is the brain tissue covering the top and sides of the brain in most vertebrates. It is involved in storing and processing of sensory inputs and motor outputs. In the human brain, the cerebral cortex is actually a sheet of neural tissue about 1/8th inch thick. The sheet is folded so that it can fit inside the skull. The neural circuits in this area of the brain expand with practice of an activity, just like the synaptic plasticity grows with practice. Clarification of some of the mechanisms of learning by neuro science has been advanced, in part, by the advent of non-invasive imaging technologies, such as positron emission tomography (PET) and functional magnetic resonance imaging (FMRI). These technologies have allowed researchers to observe human learning processes directly. Through these types of technologies, we are now able to see and study what happens in the process of learning. In different tests performed the brain being imaged showed a greater blood flow and activation to that area of the brain being stimulated through different activities such as finger tapping in a specific sequence. It has been revealed that the process at the beginning of learning a new skill happens quickly, and later on slows down to almost a plateau. This process can also be referred to as The Law of Learning. The slower learning showed in the FMRI that in the cerebral cortex this was when the long term learning was occurring, suggesting that the structural changes in the cortex reflect the enhancement of skill memories during later stages of training. When a person studies a skill for a longer duration of time, but in a shorter amount of time they will learn quickly, but also only retain the information into their short-term memory. Just like studying for an exam; if a student tries to learn everything the night before, it will not stick in the long run. If a person studies a skill for a shorter duration of time, but more frequently and long-term, their brain will retain this information much longer as it is stored in the long-term memory. Functional and structural studies of the brain have revealed a vast interconnectivity between diverse regions of the cerebral cortex. For example, large numbers of axons interconnect the posterior sensory areas serving vision, audition, and touch with anterior motor regions. Constant communication between sensation and movement makes sense, because to execute smooth movement through the environment, movement must be continuously integrated with knowledge about one's surroundings obtained via sensory perception. The cerebral cortex plays a role in allowing humans to do this.
Visual acuity
The visual cortex is the part of the cerebral cortex in the posterior part of the brain responsible for processing visual stimuli, called the occipital lobe. The central 10° of field (approximately the extension of the macula) is represented by at least 60% of the visual cortex. Many of these neurons are believed to be involved directly in visual acuity processing.
Maturity (psychological)
The pre-frontal cortex, which is responsible for higher cognitive functions such as planning, decision-making, judgment and reasoning, develops and matures most rapidly during early adolescence and into the early 20s. Accompanying the growth of the pre-frontal cortex is continued synaptic pruning (the trimming of rarely used synapses) as well as increased myelination of nerve fibers in the brain, which serves to insulate and speed up signal transmission between neurons. The incomplete development of this process contributes to the finding that adolescents use their brain less broadly than do adults when asked to inhibit a response and show less cross-talk (communication across diverse regions of the brain). The brain's "cross-talk" may be related to decision-making concerning risk-taking, with one study of American adolescents finding delayed reaction time and decreased spread across brain regions in a task asking them to determine whether a dangerous action is a good idea or not. Steinberg observes that there is close overlap in the activated brain regions for socioemotional and reward information, which may pose a challenge when making decisions in the most high-risk peer contexts. One study found that preference for small immediate rewards over larger long-term rewards was associated with increased activation with regions primarily responsible for socioemotional decision-making.
Primary somatosensory cortex
At the primary somatosensory cortex, tactile representation is orderly arranged (in an inverted fashion) from the toe (at the top of the cerebral hemisphere) to mouth (at the bottom). However, some body parts may be controlled by partially overlapping regions of cortex. Each cerebral hemisphere of the primary somatosensory cortex only contains a tactile representation of the opposite (contralateral) side of the body. The amount of primary somatosensory cortex devoted to a body part is not proportional to the absolute size of the body surface, but, instead, to the relative density of cutaneous tactile receptors on that body part. The density of cutaneous tactile receptors on a body part is generally indicative of the degree of sensitivity of tactile stimulation experienced at said body part. For this reason, the human lips and hands have a larger representation than other body parts.
Functional specialization (brain)
Studies have found the frontal lobes to be involved in the executive functions of the brain, which are higher level cognitive processes. This control process is involved in the coordination, planning and organizing of actions towards an individual's goals. It contributes to such things as one's behaviour, language and reasoning. More specifically, it was found to be the function of the prefrontal cortex, and evidence suggest that these executive functions control processes such as planning and decision making, error correction and assisting overcoming habitual responses. Miller and Cummings used PET and functional magnetic imaging (fMRI) to further support functional specialization of the frontal cortex. They found lateralization of verbal working memory in the left frontal cortex and visuospatial working memory in the right frontal cortex. Lesion studies support these findings where left frontal lobe patients exhibited problems in controlling executive functions such as creating strategies. The dorsolateral, ventrolateral and anterior cingulate regions within the prefrontal cortex are proposed to work together in different cognitive tasks, which is related to interaction theories. However, there has also been evidence suggesting strong individual specializations within this network. For instance, Miller and Cummings found that the dorsolateral prefrontal cortex is specifically involved in the manipulation and monitoring of sensorimotor information within working memory.
Auditory cortex
The auditory cortex is the part of the temporal lobe that processes auditory information in humans and other vertebrates. It is a part of the auditory system, performing basic and higher functions in hearing, such as possible relations to language switching.
Postrhinal cortex
The Postrhinal cortex is an area of the brain which borders above the entorhinal cortex. It is the cortical region dorsally adjacent and caudal to the posterior rhinal sulcus. It is implicated in the role of memory and spatial navigation.
Inferior frontal gyrus
The left opercular part of the inferior frontal gyrus is a part of the articulatory network involved in motor syllable programs. The articulatory network also contains the premotor cortex, and the anterior insula. These areas are interrelated but have specific functions in speech comprehension and production. The articulatory network acts mostly when the vocal tract moves to produce syllables. The pars opercularis acts indirectly through the motor cortex to control the motor aspect of speech production, and codes motor programs for this system, while the auditory cortex (via the temporoparietal junction in the lateral sulcus (Sylvian fissure) houses a series of sensory targets. Together, these areas function as a sensory-motor loop for syllable information coding.
Prefrontal cortex
Miller and Cohen proposed an Integrative Theory of Prefrontal Cortex Function, that arises from the original work of Goldman-Rakic and Fuster. The two theorize that “cognitive control stems from the active maintenance of patterns of activity in the prefrontal cortex that represents goals and means to achieve them. They provide bias signals to other brain structures whose net effect is to guide the flow of activity along neural pathways that establish the proper mappings between inputs, internal states, and outputs needed to perform a given task”. In essence, the two theorize that the prefrontal cortex guides the inputs and connections, which allows for cognitive control of our actions.
Cerebral cortex
The motor areas are located in both hemispheres of the cortex. They are shaped like a pair of headphones stretching from ear to ear. The motor areas are very closely related to the control of voluntary movements, especially fine fragmented movements performed by the hand. The right half of the motor area controls the left side of the body, and vice versa.
Spontaneous recovery
The pathway of recall associated with the retrieval of sound memories is the auditory system. Within the auditory system is the auditory cortex, which can be broken down into the primary auditory cortex and the belt areas. The primary auditory cortex is the main region of the brain that processes sound and is located on the superior temporal gyrus in the temporal lobe where it receives point-to-point input from the medial geniculate nucleus. From this, the primary auditory complex had a topographic map of the cochlea. The belt areas of the auditory complex receive more diffuse input from peripheral areas of the medial geniculate nucleus and therefore are less precise in tonotopic organization compared to the primary visual cortex. A 2001 study by Trama examined how different kinds of brain damage interfere with normal perception of music. One of his studied patients lost most of his auditory cortex to strokes, allowing him to still hear but making it difficult to understand music since he could not recognize harmonic patterns. Detecting a similarity between speech perception and sound perception, spontaneous recovery of lost auditory information is possible in those patients who have experienced a stroke or other major head trauma. Amusia is a disorder manifesting itself as a defect in processing pitch but also affects one's memory and recognition for music.
KE family
Neuroscientist and language expert at the Institute of Child Health, Faraneh Vargha-Khadem, began to investigate teaming up with University of Oxford and University of Reading linguists. In 1995 they found, contrary to Gopnik's hypothesis, from comparison of 13 affected and 8 normal individuals that the genetic disorder was a complex impairment of not only linguistic ability, but also intellectual and anatomical features, thereby disproving the "grammar gene" notion. Using positron emission tomography (PET) and magnetic resonance imaging (MRI), they found that some brain regions were underactive (compared to baseline levels) in the KE family members and that some were overactive, when compared to normal people. The underactive regions included motor neurons that control face and mouth regions. The areas that were overactive includes Broca's area, the speech centre. With Oxford geneticists Simon Fisher and Anthony Monaco, they identified the exact location of the gene on the long arm of chromosome 7 (7q31) in 1998. The chromosomal region (locus) was named "SPCH1" (for speech-and-language-disorder-1), and it contains 70 genes. Using the known gene location of speech disorder from a boy, designated CS, of unrelated family, they discovered in 2001 that the main gene responsible for speech impediment in both KE family and CS was "FOXP2", and that this gene plays a major role in the origin and development of language. Mutations in the genes result in speech and language problems.
Sensory gating
Information from sensory receptors make their way to the brain through neurons and synapse at the thalamus. The pulvinar nuclei in the thalamus function as the gatekeeper, deciding which information should be inhibited, and which should be sent to further cortical areas. Sensory gating is mediated by a network in the brain which involves the auditory cortex (AC), prefrontal cortex and hippocampus. Other areas of the brain associated with sensory gating include the amygdala, striatum, medial prefrontal cortex, and midbrain dopamine cell region (GABAergic neurons only).
Research of sensory gating primarily occurs in cortical areas where the stimulus is consciously identified because it is a less invasive means of studying sensory gating. Studies on rats show the brain stem, thalamus, and primary auditory cortex play a role in sensory gating for auditory stimuli.
Human brain
The human brain is the central organ of the human nervous system, and with the spinal cord makes up the central nervous system. The brain consists of the cerebrum, the brainstem and the cerebellum. It controls most of the activities of the body, processing, integrating, and coordinating the information it receives from the sense organs, and making decisions as to the instructions sent to the rest of the body. The brain is contained in, and protected by, the skull bones of the head. 
The cerebrum is the largest part of the human brain. It is divided into two cerebral hemispheres. The cerebral cortex is an outer layer of grey matter, covering the core of white matter. The cortex is split into the neocortex and the much smaller allocortex. The neocortex is made up of six neuronal layers, while the allocortex has three or four. Each hemisphere is conventionally divided into four lobes – the frontal, temporal, parietal, and occipital lobes. The frontal lobe is associated with executive functions including self-control, planning, reasoning, and abstract thought, while the occipital lobe is dedicated to vision. Within each lobe, cortical areas are associated with specific functions, such as the sensory, motor and association regions. Although the left and right hemispheres are broadly similar in shape and function, some functions are associated with one side, such as language in the left and visual-spatial ability in the right. The hemispheres are connected by commissural nerve tracts, the largest being the corpus callosum.
National Institutes of Health Stroke Scale
Dysarthria is the lack of motor skills required to produce understandable speech. Dysarthria is strictly a motor problem, and is not related to the patient's ability to comprehend speech. Strokes that cause dysarthria typically affect areas such as the anterior opercular, medial prefrontal and premotor, and anterior cingulate regions. These brain regions are vital in coordinating motor control of the tongue, throat, lips, and lungs. To perform this item the patient is asked to read from the list of words provided with the stroke scale while the examiner observes the patient's articulation and clarity of speech.
Arcuate fasciculus
Evidence for the role of the arcuate fasciculus in language use is best represented by conduction aphasia, caused by damage to the inferior parietal lobule that extends into the subcortical white matter and damages the arcuate fasciculus. This type of aphasia inhibits the patient from repeating unfamiliar sounds. A study by Catani, Jones, and Ffytche (2005) provided the first anatomical evidence for the presence of two pathways between Wernicke’s area and Broca’s area. They found one deep pathway, interpreted to directly connect these two regions, and a shallower pathway that consists of two segments; the anterior segment connects frontal cortex with inferior parietal cortex, and the posterior segment connects Wernicke’s area with the inferior parietal cortex. Damage to the direct pathway may produce conduction aphasia, whereas damage to the indirect pathway spares the ability to repeat speech but impairs comprehension. The symptoms of conduction aphasia suggest that the connection between posterior temporal cortex and frontal cortex plays a vital role in short-term memory of words and speech sounds that are new or have just been heard. The arcuate fasciculus connects these two regions and circulates information back and forth, possibly contributing to short-term memory.
Superior temporal gyrus
The superior temporal gyrus contains the auditory cortex, which is responsible for processing sounds. Specific sound frequencies map precisely onto the auditory cortex. This auditory (or tonotopic) map is similar to the homunculus map of the primary motor cortex. Some areas of the superior temporal gyrus are specialized for processing combinations of frequencies, and other areas are specialized for processing changes in amplitude or frequency. The superior temporal gyrus also includes the Wernicke's area, which (in most people) is located in the left hemisphere. It is the major area involved in the comprehension of language. The superior temporal gyrus (STG) is involved in auditory processing, including language, but also has been implicated as a critical structure in social cognition.
Delayed Auditory Feedback
Studies using computational modeling and functional magnetic resonance imaging (fMRI) have shown that the temporo-parietal regions function as a conscious self-monitoring system to support an automatic speech production system and that projections from auditory error cells in the posterior superior temporal cortex that go to motor correction cells in right frontal cortex mediate auditory feedback control of speech.
Expressive aphasia
In most cases, expressive aphasia is caused by a stroke in Broca's area or the surrounding vicinity. Broca's area is in the lower part of the premotor cortex in the language dominant hemisphere and is responsible for planning motor speech movements. However, cases of expressive aphasia have been seen in patients with strokes in other areas of the brain. Patients with classic symptoms of expressive aphasia in general have more acute brain lesions, whereas patients with larger, widespread lesions exhibit a variety of symptoms that may be classified as global aphasia or left unclassified.
Frontal lobe disorder
The frontal lobe contains the precentral gyrus and prefrontal cortex and, by some conventions, the orbitofrontal cortex. These three areas are represented in both the left and the right cerebral hemispheres.The precentral gyrus or primary motor cortex is concerned with the planning, initiation and control of fine motor movements dorsolateral to each hemisphere. The dorsolateral part of the frontal lobe is concerned with planning, strategy formation, and other executive functions. The prefrontal cortex in the left hemisphere is involved with verbal memory while the prefrontal cortex in the right hemisphere is involved in spatial memory. The left frontal operculum region of the prefrontal cortex, or Broca's area, is responsible for expressive language, i.e. language production. The orbitofrontal cortex is concerned with response inhibition, impulse control, and social behaviour.
Auditory system
The primary auditory cortex is the first region of cerebral cortex to receive auditory input.
Evolution of the brain
The area of the brain with the greatest amount of recent evolutionary change is called the cerebrum, or neocortex. In reptiles and fish, this area is called the pallium, and is smaller and simpler relative to body mass than what is found in mammals. According to research, the cerebrum first developed about 200 million years ago. It's responsible for higher cognitive functions - for example, language, thinking, and related forms of information processing. It's also responsible for processing sensory input (together with the thalamus, a part of the limbic system that acts as an information router). Most of its function is subconscious, that is, not available for inspection or intervention by the conscious mind. Neocortex is an elaboration, or outgrowth, of structures in the limbic system, with which it is tightly integrated.
Language center
Most areas of speech processing develop in the second year of life in the dominant half (hemisphere) of the brain, which often (though not necessarily) corresponds to the opposite of the dominant hand. 98% of right-handed people are left-hemisphere dominant, and the majority of left-handed people as well.
Language acquisition
Although it is difficult to determine without invasive measures which exact parts of the brain become most active and important for language acquisition, fMRI and PET technology has allowed for some conclusions to be made about where language may be centered. Kuniyoshi Sakai proposed, based on several neuroimaging studies, that there may be a "grammar center", where language is primarily processed in the left lateral premotor cortex (located near the pre central sulcus and the inferior frontal sulcus). Additionally, these studies proposed that first language and second-language acquisition may be represented differently in the cortex.
In a study conducted by Newman et al., the relationship between cognitive neuroscience and language acquisition was compared through a standardized test procedure involving native speakers of English and native Spanish speakers who have all had a similar amount of exposure to the English language(averaging about 26 years). Even the number of times an examinee blinked was taken into account during the examination process. It was concluded that the brain does in fact process languages differently, but instead of it being directly related to proficiency levels, it is more so about how the brain processes language itself.
Damasio's theory of consciousness
Multiple brain areas are required for the Protoself to function. Namely, the hypothalamus, which controls the general homeostasis of the organism, the brain stem, whose nuclei map body signals, and the insular cortex whose function is linked to emotion. These brain areas work together to keep up with the constant process of collecting neural patterns to map the current status of the body's responses to environmental changes. The Protoself does not require language in order to function, moreover it is a direct report of one's experience.
Language processing in the brain
The auditory dorsal stream connects the auditory cortex with the parietal lobe, which in turn connects with inferior frontal gyrus. In both humans and non-human primates, the auditory dorsal stream is responsible for sound localization, and is accordingly known as the auditory 'where' pathway. In humans, this pathway (especially in the left hemisphere) is also responsible for speech production, speech repetition, lip-reading, and phonological working memory and long-term memory.
Stuttering
During speech production, people who stutter show overactivity in the anterior insula, cerebellum and bilateral midbrain. They show underactivity in the ventral premotor, Rolandic opercular and sensorimotor cortex bilaterally and Heschl’s gyrus in the left hemisphere. Additionally, speech production in people who stutter yields underactivity in cortical motor and premotor areas.
Auditory cortex
Neurons in the auditory cortex are organized according to the frequency of sound to which they respond best. Neurons at one end of the auditory cortex respond best to low frequencies; neurons at the other respond best to high frequencies. There are multiple auditory areas (much like the multiple areas in the visual cortex), which can be distinguished anatomically and on the basis that they contain a complete "frequency map." The purpose of this frequency map (known as a tonotopic map) is unknown, and is likely to reflect the fact that the cochlea is arranged according to sound frequency. The auditory cortex is involved in tasks such as identifying and segregating "auditory objects" and identifying the location of a sound in space. For example, it has been shown that A1 encodes complex and abstract aspects of auditory stimuli without encoding their "raw" aspects like frequency content, presence of a distinct sound or its echoes.
Dentate nucleus
The dentate contains anatomically separate and functionally distinct motor and nonmotor domains (dorsal and ventral, respectively), and projections are organized from the dentate nucleus to distinct areas in the ventrolateral thalamus. In addition, the dorsal parts of the dentate project to the primary motor and premotor areas of the cerebral cortex, while the ventral parts of the dentate project to prefrontal and posterior parietal areas of the cerebral cortex. The motor and nonmotor domains make up approximately 50–60 percent and 20 percent, respectively, of the dentate. It is estimated that the human dentate proportions are comparable. All cerebral cortical areas that are targeted by the dentate project back on the cerebellum via efferents to Pontine nuclei, and cortical areas that do not project onto the cerebellum are not targets of dentate output.
The motor domain in the dorsal portion of the dentate contains output channels that control both generation and control of movement, as well as neurons that innervate premotor areas in the frontal lobe. 
The nonmotor domain contains output channels involved in cognition and visuospatial function, and projections to the prefrontal and posterior parietal cortical areas within this region are clustered into distinct regions with little overlap. These areas are activated during tasks involving short-term working memory, rule-based learning, and higher executive function-like planning. Although the ventral aspect of the dentate has been shown to be involved in acquisition of information, whether it is involved in retention and storage remains unclear.
Neuroscience of multilingualism
The brain contains areas that are specialized to deal with language, located in the perisylvian cortex of the left hemisphere. These areas are crucial for performing language tasks, but they are not the only areas that are used; disparate parts of both right and left brain hemispheres are active during language production. In multilingual individuals, there is a great deal of similarity in the brain areas used for each of their languages. Insights into the neurology of multilingualism have been gained by the study of multilingual individuals with aphasia, or the loss of one or more languages as a result of brain damage. Bilingual aphasics can show several different patterns of recovery; they may recover one language but not another, they may recover both languages simultaneously, or they may involuntarily mix different languages during language production during the recovery period. These patterns are explained by the "dynamic view" of bilingual aphasia, which holds that the language system of representation and control is compromised as a result of brain damage.
Sex differences in human physiology
There are also differences in the structure of and in specific areas of the brain. On average, the SDN has been repeatedly found to be considerably larger in males than in females. The volume of the SDN was 2.2 times as large in males as in females. On average, the BSTc is twice as large in men as in women. On average, the INAH-3 is significantly larger in males than in females regardless of age. Two studies found that men have larger parietal lobes, an area responsible for sensory input including spatial sense and navigation; though, another study failed to find any statistically significant difference. At the same time, females have larger Wernicke's and Broca's areas, areas responsible for language processing. Studies using MRI scanning have shown that the auditory and language-related regions in the left hemisphere are proportionally expanded in females versus in males. Conversely, the primary visual, and visuo-spatial association areas of the parietal lobes are proportionally larger in males. The corpus callous is located at the sagittal divide and is the primary commissure in the human brain. It connects the left and right hemispheres of the cerebral cortex, which allows them to communicate with each other. With respect to language, males predominantly use their left hemisphere but females use both their right and left hemispheres. The right hemisphere controls emotion, so using the right hemisphere adds more prosody to speech. In males, the corpus callosum is larger than females. However, the splenium and the isthmus subregions of the corpus callosum are larger in females. The genu subregion is larger in males. These subregions may serve as the basis for sex differences in language. However, a 1997 meta-study concluded that there is no relative size difference, and that the larger corpus callosum in males is due to generally larger brains in males on average.
In total and on average, females have a higher percentage of grey matter in comparison to males, and males a higher percentage of white matter. However, some researchers maintain that as males have larger brains on average than females, when adjusted for total brain volume, the grey matter differences between sexes is small or nonexistent. Thus, the percentage of grey matter appears to be more related to brain size than it is to gender.
Evolution of the brain
The cerebellum, or "little brain," is behind the brainstem and below the occipital lobe of the cerebrum in humans. Its purposes include the coordination of fine sensorimotor tasks, and it may be involved in some cognitive functions, such as language. Human cerebellar cortex is finely convoluted, much more so than cerebral cortex. Its interior axon fiber tracts are called the "arbor vitae", or Tree of Life.
Orbitofrontal cortex
The orbitofrontal cortex (OFC) is a prefrontal cortex region in the frontal lobes of the brain which is involved in the cognitive process of decision-making. In non-human primates it consists of the association cortex areas Brodmann area 11, 12 and 13; in humans it consists of Brodmann area 10, 11 and 47.
Tip of the tongue
Not much is known about the exact function of these areas in the tip-of-the-tongue phenomenon. The areas activated during TOT may vary depending on the nature of the target word. For example, if the target word is a person's name, the fusiform face area will likely show activation as the rememberer processes the person's face. Problems like this make it difficult to determine what areas are specifically implicated in TOT states, and which are a byproduct of other cognitive functions. However, some inferences can be made about the roles of these structures based on theories of their functions derived from other studies of these structures, unrelated to TOT. It is hypothesized that the anterior cingulate cortex and the right dorsolateral prefrontal cortex operate as a circuit to detect conflict, and may perform this role in detecting the conflict between the feeling of knowing the target word and the recall failure. The anterior cingulate cortex is also implicated in emotion and may show activation because of the emotional response to the tip of the tongue state. The posterior medial parietal cortex, bilateral lateral parietal cortex, and the bilateral superior prefrontal cortex are involved in retrieval and evaluation, and therefore may play a role in the metacognitive processes involved in the tip of the tongue phenomenon such as the evaluation of one's own knowledge and the probability of retrieval.
Echoic memory
Auditory sensory memory has been found to be stored in the primary auditory cortex contralateral to the ear of presentation. This echoic memory storage involves several different brain areas, due to the different processes it is involved in. The majority of brain regions involved are located in the prefrontal cortex (PFC) as this is where the executive control is located, and is responsible for attentional control. The phonological store and the rehearsal system appear to be a left-hemisphere based memory system as increased brain activity has been observed in these areas. The major regions involved are the left posterior ventrolateral prefrontal cortex (VLPFC), the left premotor cortex (PMC), and the left posterior parietal cortex (PPC). Within the VLPFC, Broca's area is the main location responsible for verbal rehearsal and the articulatory process. The dorsal PMC is used in rhythmic organization and rehearsal, and finally the PPC shows a role in localizing objects in space.
Ultrasonic vocalization
The larynx has been implicated in the production of ultrasonic vocalizations. A constriction within a rat’s larynx is thought to be the source of their ultrasonic vocalizations. As well, brain areas such as the medulla oblongata, the cortex, the amygdala, and the dorsal hippocampus, among others, play a role in 22-kHz calls specifically. Many of these brain areas/structures have been implicated in studies involving fear and anxiety, and can be associated with a larger network which deals with aversive emotions.
Temporal envelope and fine structure
Responses to the temporal-envelope cues of speech or other complex sounds persist up the auditory pathway, eventually to the various fields of the auditory cortex in many animals. In the Primary Auditory Cortex, responses can encode AM rates by phase-locking up to about 20–30 Hz, while faster rates induce sustained and often tuned responses. A topographical representation of AM rate has been demonstrated in the primary auditory cortex of awake macaques. This representation is approximately perpendicular to the axis of the tonotopic gradient, consistent with an orthogonal organization of spectral and temporal features in the auditory cortex. Combining these temporal responses with the spectral selectivity of A1 neurons gives rise to the spectro-temporal receptive fields that often capture well cortical responses to complex modulated sounds. In secondary auditory cortical fields, responses become temporally more sluggish and spectrally broader, but are still able to phase-lock to the salient features of speech and musical sounds. Tuning to AM rates below about 64 Hz is also found in the human auditory cortex as revealed by brain-imaging techniques (fMRI) and cortical recordings in epileptic patients (electrocorticography). This is consistent with neuropsychological studies of brain-damaged patients and with the notion that the central auditory system performs some form of spectral decomposition of the ENVp of incoming sounds. The ranges over which cortical responses encode well the temporal-envelope cues of speech have been shown to be predictive of the human ability to understand speech. In the human superior temporal gyrus (STG), an anterior-posterior spatial organization of spectro-temporal modulation tuning has been found in response to speech sounds, the posterior STG being tuned for temporally fast varying speech sounds with low spectral modulations and the anterior STG being tuned for temporally slow varying speech sounds with high spectral modulations.