How are brain waves measured?
Body &amp; Brain
"Brain Wave Vibration" is promoted as a mental and physical health enhancement technique developed by Ilchi Lee. According to Lee, brain waves are a type of vibration that has a significant effect on a person’s health and outlook on life. A form of moving meditation (head-shaking), the technique was described by one Body & Brain instructor: "By shaking your head and vibrating your body, you bring healing energy. You just need to close your eyes and turn your head right and left, right and left, focusing on the center of your brain and keeping a rhythm. Afterwards, you feel very rejuvenated!" As part of CNN's three-part investigation into controversy and lawsuits surrounding Dahn Yoga, Neurosurgeon Dr. Sanjay Gupta was asked about testimonials that Brain Wave Vibration "lowered blood pressure, corrected lazy eyes, [and] even reduced symptoms of multiple sclerosis." Gupta stated that the notion of vibrating the brain or other parts of the body to turn parts of the brain on and off is not grounded in science and that anecdotes are not empirically verifiable.
Mu wave
Mu waves, also known as mu rhythms, comb or wicket rhythms, arciform rhythms, or sensorimotor rhythms, are synchronized patterns of electrical activity involving large numbers of neurons, probably of the pyramidal type, in the part of the brain that controls voluntary movement. These patterns as measured by electroencephalography (EEG), magnetoencephalography (MEG), or electrocorticography (ECoG), repeat at a frequency of 7.5–12.5 (and primarily 9–11) Hz, and are most prominent when the body is physically at rest. Unlike the alpha wave, which occurs at a similar frequency over the resting visual cortex at the back of the scalp, the mu wave is found over the motor cortex, in a band approximately from ear to ear. A person suppresses mu wave patterns when he or she performs a motor action or, with practice, when he or she visualizes performing a motor action. This suppression is called desynchronization of the wave because EEG wave forms are caused by large numbers of neurons firing in synchrony. The mu wave is even suppressed when one observes another person performing a motor action or an abstract motion with biological characteristics. Researchers such as V. S. Ramachandran and colleagues have suggested that this is a sign that the mirror neuron system is involved in mu wave suppression, although others disagree.
Ryan D'Arcy
In 2013, D’Arcy's work was highlighted in a new brain imaging framework specific to the monitoring brain function recovery, and he coined a new neuroscience terminology, “brain vital signs” or the measurement of brain waves, similar to the measurement of a body's vital signs like blood pressure.
BrainGate
In its current form, BrainGate consists of a sensor implanted in the brain and an external decoder device, which connects to some kind of prosthetic or other external object. The sensor is in the form of a Multielectrode array, formerly known as the Utah Array, which consists of 100 hair-thin electrodes that sense the electromagnetic signature of neurons firing in specific areas of the brain, for example, the area that controls arm movement. The sensor translates that activity into electrically charged signals, which are then sent to an external device and decoded in software. The decoder connects to and can use the brain signals to control an external device, such as a robotic arm, a computer cursor, or even a wheelchair. In essence, BrainGate allows a person to manipulate objects in the world using only the mind.
In addition to real-time analysis of neuron patterns to relay movement, the BrainGate array is also capable of recording electrical data for later analysis. A potential use of this feature would be for a neurologist to study seizure patterns in a patient with epilepsy.
BrainGate was originally developed by researchers in the Department of Neuroscience at Brown University in conjunction with bio-tech company Cyberkinetics, Inc. Cyberkinetics later spun off the device manufacturing to Blackrock Microsystems, who now manufactures the sensors and the data acquisition hardware. The BrainGate Company purchased the intellectual property and related technology from Cyberkinetics and continues to own the intellectual property related to BrainGate.
Brain morphometry
With the exception of the usually slice-based histology of the brain, neuroimaging data are generally stored as matrices of voxels. The most popular morphometric method, thus, is known as Voxel-based morphometry (VBM; cf. ; ; ). Yet as an imaging voxel is not a biologically meaningful unit, other approaches have been developed that potentially bear a closer correspondence to biological structures: Deformation-based morphometry (DBM), surface-based morphometry (SBM) and fiber tracking based on diffusion-weighted imaging (DTI or DSI). All four are usually performed based on Magnetic Resonance (MR) imaging data, with the former three commonly using T1-weighted (e.g. Magnetization Prepared Rapid Gradient Echo, MP-RAGE) and sometimes T2-weighted pulse sequences, while DTI/DSI use diffusion-weighted ones. However, recent evaluation of morphometry algorithms/software demonstrates inconsistency among several of them. This renders a need for systematic and quantitative validation and evaluation of the field.
Archie Frederick Collins
An unusual example were his experiments in using brain tissue to detect radio waves. The first radio receivers prior to 1904 used a primitive device called a coherer to detect the radio waves. The poor performance of the coherer led to much research to find a better radio wave detector. Collins was intrigued by reports of people "predicting weather" by aches and pains in their body, and examples of lightning strikes, which were strong sources of radio waves, causing convulsions in nearby people who were not actually struck. Since the brain was known to operate electrically, Collins thought it might be sensitive to radio waves. He applied DC current from a battery to two electrodes in dissected animal brains, causing a small current through the tissue, as in a coherer. Then he radiated the brain with pulses of radio waves from a Hertzian spark radio transmitter, and listened with earphones to the circuit. If the radio waves caused changes in the conductivity of the neural tissue, it would cause transient changes in the current, which would be audible as "clicks" in the earphones. His research culminated in experiments on a fresh human brain from a cadaver. Collins claimed that the brain had a 'cohering' effect, its conductivity changed when irradiated. However other researchers were unable to reproduce the effect.
The "spark" radio transmitters during Collins time could not transmit sound (audio) as modern AM and FM radio transmitters do. This was because the discharge of a spark cannot produce continuous waves, but only damped waves. Instead they transmitted information by telegraphy, the operator turned the transmitter off and on by tapping on a switch called a telegraph key to produce different length pulses of damped radio waves, to spell out text messages in Morse code. By the last years of the century, many wireless researchers such as Reginald Fessenden, Ernst Ruhmer, William Dubilier, Quirino Majorana, and Valdemar Poulsen were working to develop continuous wave transmitters which could be modulated to carry sound, radiotelephony.
Single-unit recording
There are many techniques available to record brain activity—including electroencephalography (EEG), magnetoencephalography (MEG), and functional magnetic resonance imaging (fMRI)—but these do not allow for single-neuron resolution. Neurons are the basic functional units in the brain; they transmit information through the body using electrical signals called action potentials. Currently, single-unit recordings provide the most precise recordings from single neurons. A single unit is defined as a single, firing neuron whose spike potentials are distinctly isolated by a recording microelectrode.
Delta wave
A delta wave is a high amplitude brain wave with a frequency of oscillation between 0.5–4 hertz. Delta waves, like other brain waves, are recorded with an electroencephalogram (EEG) and are usually associated with the deep stage 3 of NREM sleep, also known as slow-wave sleep (SWS), and aid in characterizing the depth of sleep.
Napoleon Cybulski
In 1890 Cybulski carried out one of the first-ever EEG recordings of the cerebral cortex. Working with Adolf Beck (1863–1942), he conducted pioneering research on electroencephalographic waves. Under Cybulski’s supervision, Beck made pioneering studies of cerebral-cortex activity in response to peripheral-nerve stimulation in dogs and monkeys, using electrodes placed on the skull to record changes in electric potential. In this way they invalidated William Horsley’s notion that these changes reflected the activity of skull muscles. By further analyses of potential changes, they mapped out sensory regions of the cerebral cortex. They also provided evidence that the amplitude of signals depended on the strength and kind of sensory stimulus and on the depth of anesthesia. They suspected that brain function was mediated by neurons' bioelectrical activity. Their studies on brain mapping and nerve stimulation were absolutely innovative, since they were unfamiliar with earlier research done by Richard Caton on changes in bioelectrical activity of the dog brain during sleep, activity, and changes in behavior.
Omegawave
The key to Omegawave's system is the way the software, developed by Vladimir Larionov and Leonid Masakov, interprets electrocardiography (EKG), and a very slow moving♙Omega brain wave, and compares them with each other to determine an individual's current physical state.
Brainwave entrainment
Brainwaves, or neural oscillations, share the fundamental constituents with acoustic and optical waves, including frequency, amplitude and periodicity. Consequently, Huygens' discovery precipitated inquiry into whether or not the synchronous electrical activity of cortical neural ensembles might not only alter in response to external acoustic or optical stimuli but also entrain or synchronize their frequency to that of a specific stimulus.
Pulse wave velocity
Clinically, PWV can be measured in several ways and in different locations. The 'gold standard' for arterial stiffness assessment in clinical practice is cfPWV, and validation guidelines have been proposed. Other measures such as brachial-ankle PWV and cardio-ankle vascular index (CAVI) are also popular. For cfPWV, it is recommended that the arrival time of the pulse wave measured simultaneously at both locations, and the distance travelled by the pulse wave calculated as 80% of the direct distance between the common carotid artery in the neck and the femoral artery in the groin. Numerous devices exist to measure cfPWV; some techniques include:Newer devices that employ an arm cuff, fingertip sensors or special weighing scales have been described, but their clinical utility remains to be fully established.
Brain
Sleep involves great changes in brain activity. Until the 1950s it was generally believed that the brain essentially shuts off during sleep, but this is now known to be far from true; activity continues, but patterns become very different. There are two types of sleep: "REM sleep" (with dreaming) and "NREM" (non-REM, usually without dreaming) sleep, which repeat in slightly varying patterns throughout a sleep episode. Three broad types of distinct brain activity patterns can be measured: REM, light NREM and deep NREM. During deep NREM sleep, also called slow wave sleep, activity in the cortex takes the form of large synchronized waves, whereas in the waking state it is noisy and desynchronized. Levels of the neurotransmitters norepinephrine and serotonin drop during slow wave sleep, and fall almost to zero during REM sleep; levels of acetylcholine show the reverse pattern.
Neural oscillation
Neural oscillations have been most widely studied in neural activity generated by large groups of neurons. Large-scale activity can be measured by techniques such as EEG. In general, EEG signals have a broad spectral content similar to pink noise, but also reveal oscillatory activity in specific frequency bands. The first discovered and best-known frequency band is alpha activity (8–12 Hz) that can be detected from the occipital lobe during relaxed wakefulness and which increases when the eyes are closed. Other frequency bands are: delta (1–4 Hz), theta (4–8 Hz), beta (13–30 Hz), low gamma (30–70 Hz), and high gamma (70–150 Hz) frequency bands, where faster rhythms such as gamma activity have been linked to cognitive processing. Indeed, EEG signals change dramatically during sleep and show a transition from faster frequencies to increasingly slower frequencies such as alpha waves. In fact, different sleep stages are commonly characterized by their spectral content. Consequently, neural oscillations have been linked to cognitive states, such as awareness and consciousness.
Human brain
Information about the structure and function of the human brain comes from a variety of experimental methods, including animals and humans. Information about brain trauma and stroke has provided information about the function of parts of the brain and the effects of brain damage. Neuroimaging is used to visualise the brain and record brain activity. Electrophysiology is used to measure, record and monitor the electrical activity of the cortex. Measurements may be of local field potentials of cortical areas, or of the activity of a single neuron. An electroencephalogram can record the electrical activity of the cortex using electrodes placed non-invasively on the scalp.
Neural oscillation
Neural oscillations are observed throughout the central nervous system at all levels, and include spike trains, local field potentials and large-scale oscillations which can be measured by electroencephalography (EEG). In general, oscillations can be characterized by their frequency, amplitude and phase. These signal properties can be extracted from neural recordings using time-frequency analysis. In large-scale oscillations, amplitude changes are considered to result from changes in synchronization within a neural ensemble, also referred to as local synchronization. In addition to local synchronization, oscillatory activity of distant neural structures (single neurons or neural ensembles) can synchronize. Neural oscillations and synchronization have been linked to many cognitive functions such as information transfer, perception, motor control and memory.
Hans Thewissen
Thewissen’s current work involves counting neurons in bowhead and beluga whale brain samples, to assess brain function, in Utqiagvik—formerly Barrow—Alaska. Though the size of the brains of sperm whales and killer whales are larger than those of any other organism, including humans, a better measure of brain function is to determine how many neurons there are in the brain. Suzana Herculano-Houzel has developed a method of counting of neurons of human and other animals' brains and the relation between the cerebral cortex area and thickness and number of cortical folds. Humans and other primates pack about twice the number of neurons in a cubed inch of brain as most other mammals.
Noise
Sound is measured based on the amplitude and frequency of a sound wave. Amplitude measures how forceful the wave is. The energy in a sound wave is measured in decibels (dB), the measure of loudness, or intensity of a sound; this measurement describes the amplitude of a sound wave. Decibels (dB) are expressed in a logarithmic scale. On the other hand, pitch describes the frequency of a sound and is measured in hertz (Hz).
Neurotechnology
Magnetoencephalography is a functional neuroimaging technique for mapping brain activity by recording magnetic fields produced by electrical currents occurring naturally in the brain, using very sensitive magnetometers. Arrays of SQUIDs (superconducting quantum interference devices) are the most common magnetometer. Applications of MEG include basic research into perceptual and cognitive brain processes, localizing regions affected by pathology before surgical removal, determining the function of various parts of the brain, and neurofeedback. This can be applied in a clinical setting to find locations of abnormalities as well as in an experimental setting to simply measure brain activity.
PGO waves
Ponto-geniculo-occipital waves or PGO waves are phasic field potentials. These waves can be recorded from the pons, the lateral geniculate nucleus (LGN), and the occipital cortex regions of the brain, where these waveforms originate. The waves begin as electrical pulses from the pons, then move to the lateral geniculate nucleus residing in the thalamus, and then finally end up in the primary visual cortex of the occipital lobe. The appearances of these waves are most prominent in the period right before rapid eye movement sleep (or REM sleep), and are theorized to be intricately involved with eye movement of both wake and sleep cycles in many different animals.
The discovery of PGO waves goes back to 1959, when three French scientists released their scientific article of their study of these waves in animal test subjects. Although at this time, they did not have a specific name for this neurological phenomenon.
Brain wave (disambiguation)
Brain waves are rhythmic or repetitive neural activity in the central nervous system.
Metastability in the brain
EEG measures the gross electrical activity of the brain that can be observed on the surface of the skull. In the metastability theory, EEG outputs produce oscillations that can be described as having identifiable patterns that correlate with each other at certain frequencies. Each neuron in a neuronal network normally outputs a dynamical oscillatory waveform, but also has the ability to output a chaotic waveform. When neurons are integrated into the neural network by interfacing neurons with each other, the dynamical oscillations created by each neuron can be combined to form highly predictable EEG oscillations.
Brain activity and meditation
Electroencephalography (EEG) has been used in many studies as a primary method for evaluating the meditating brain. Electroencephalography uses electrical leads placed all over the scalp to measure the collective electrical activity of the cerebral cortex. Specifically, EEG measures the electric fields of large groups of neurons. EEG has the benefit of excellent temporal resolution and is able to measure aggregate activity of portions or the entire cortex down to the millisecond scale. Unlike other imaging based methods, EEG does not have good spatial resolution and is more appropriately used to evaluate the running spontaneous activity of the cortex. This spontaneous activity is classified into four main classifications based on the frequency of the activity, ranging from low frequency delta waves (< 4 Hz) commonly found during sleep to beta waves (13–30 Hz) associated with an awake and alert brain. In between these two extremes are theta waves (4–8 Hz) and alpha waves (8–12 Hz).
Neurotechnology
Magnetic resonance imaging is a vital tool in neurological research in showing activation in the brain as well as providing a comprehensive image of the brain being studied. While MRIs are used clinically for showing brain size, it still has relevance in the study of brains because it can be used to determine extent of injuries or deformation. These can have a significant effect on personality, sense perception, memory, higher order thinking, movement, and spatial understanding. However, current research tends to focus more so on fMRI or real-time functional MRI (rtfMRI). These two methods allow the scientist or the participant, respectively, to view activation in the brain. This is incredibly vital in understanding how a person thinks and how their brain reacts to a person's environment, as well as understanding how the brain works under various stressors or dysfunctions. Real-time functional MRI is a revolutionary tool available to neurologists and neuroscientists because patients can see how their brain reacts to stressors and can perceive visual feedback. CT scans are very similar to MRI in their academic use because they can be used to image the brain upon injury, but they are more limited in perceptual feedback. CTs are generally used in clinical studies far more than in academic studies, and are found far more often in a hospital than a research facility. PET scans are also finding more relevance in academia because they can be used to observe metabolic uptake of neurons, giving researchers a wider perspective about neural activity in the brain for a given condition. Combinations of these methods can provide researchers with knowledge of both physiological and metabolic behaviors of loci in the brain and can be used to explain activation and deactivation of parts of the brain under specific conditions.
Electroencephalography
Most of the cerebral signal observed in the scalp EEG falls in the range of 1–20 Hz (activity below or above this range is likely to be artifactual, under standard clinical recording techniques). Waveforms are subdivided into bandwidths known as alpha, beta, theta, and delta to signify the majority of the EEG used in clinical practice.
Fetal EEG
Fetal electroencephalography, also known as prenatal EEG includes any recording of electrical fluctuations arising from the brain of an unborn child.  Doctors and scientists use EEGs to detect and characterize brain activity, such as sleep states, potential seizures, or levels of a coma. EEG captures the electrical activity in the vicinity of the recording electrodes. The majority of the neural electrical activity arises from the flow of current from the cell bodies of pyramidal neurons to their apical dendrites, which become depolarized by excitatory inputs from other neurons. To record the most accurate signals, scientists try to minimize the distance between the recording electrode and the neural activity that they want to detect. Given the difficulty of attaching electrodes to a fetus inside a uterus, doctors and scientists use a variety of techniques to record fetal brain activity.
Alpha wave
Berger took a cue from Ukrainian physiologist Vladimir Pravdich-Neminsky, who used a string galvanometer to create a photograph of the electrical activity of a dog's brain. Using similar techniques, Berger confirmed the existence of electrical activity in the human brain. He first did this by presenting a stimulus to hospital patients with skull damage and measuring the electrical activity in their brains. Later he ceased the stimulus method and began measuring the natural rhythmic electrical cycles in the brain. The first natural rhythm he documented was what would become known as the alpha wave. Berger was very thorough and meticulous in his data-gathering, but despite his brilliance, he did not feel confident enough to publish his discoveries until at least five years after he had made them. In 1929, he published his first findings on alpha waves in the journal "Archiv für Psychiatrie". He was originally met with derision for his EEG technique and his subsequent alpha and beta wave discoveries. His technique and findings did not gain widespread acceptance in the psychological community until 1937, when he gained the approval of the famous physiologist Lord Adrian, who took a particular interest in alpha waves.
Amigdalae
Crucial elements in the study of psychological states are cardiac frequency, electro muscular activity EMG, and body temperature. Their interpretation gives a detailed response about the psychic activity of an individual.
The average time for tracking and recording the data is seven minutes. The generated graph is based on a detailed interpretation of the four types of brain waves: alpha, beta, delta and theta. Their values are shown in amplitude (volts), frequency (hertz), and isolated peaks of electrical activity: the amplitude is higher than hundred volts and low in frequency, or short shocks of high frequency waves and small amplitude.
Event-related potential
ERPs can be reliably measured using electroencephalography (EEG), a procedure that measures electrical activity of the brain over time using electrodes placed on the scalp. The EEG reflects thousands of simultaneously ongoing brain processes. This means that the brain response to a single stimulus or event of interest is not usually visible in the EEG recording of a single trial. To see the brain's response to a stimulus, the experimenter must conduct many trials and average the results together, causing random brain activity to be averaged out and the relevant waveform to remain, called the ERP.
Brain
As a side effect of the electrochemical processes used by neurons for signaling, brain tissue generates electric fields when it is active. When large numbers of neurons show synchronized activity, the electric fields that they generate can be large enough to detect outside the skull, using electroencephalography (EEG) or magnetoencephalography (MEG). EEG recordings, along with recordings made from electrodes implanted inside the brains of animals such as rats, show that the brain of a living animal is constantly active, even during sleep. Each part of the brain shows a mixture of rhythmic and nonrhythmic activity, which may vary according to behavioral state. In mammals, the cerebral cortex tends to show large slow delta waves during sleep, faster alpha waves when the animal is awake but inattentive, and chaotic-looking irregular activity when the animal is actively engaged in a task. During an epileptic seizure, the brain's inhibitory control mechanisms fail to function and electrical activity rises to pathological levels, producing EEG traces that show large wave and spike patterns not seen in a healthy brain. Relating these population-level patterns to the computational functions of individual neurons is a major focus of current research in neurophysiology.
Electroencephalophone
An electroencephalophone or encephalophone is an experimental musical instrument and diagnostic tool which uses brain waves (measured in the same way as an EEG) to generate or modulate sounds.
Level sensor
Microwave sensors are executed in a wide variety of techniques. Two basic signal processing techniques are applied, each offering its own advantages: Pulsed or Time-Domain Reflectometry (TDR) which is a measurement of time of flight divided by the speed of light, similar to ultrasonic level sensors, and Doppler systems employing FMCW techniques. Just as with ultrasonic level sensors, microwave sensors are executed at various frequencies, from 1 GHz to 60 GHz. Generally, the higher the frequency, the more accurate, and the more costly. Microwave is executed non-contact technique or guided. The first is done by monitoring a microwave signal that is transmitted through free space (including vacuum) and reflected back, or can be executed as a "radar on a wire" technique, generally known as Guided Wave Radar or Guided Microwave Radar. In the latter technique, performance generally improves in powders and low dielectric media that are not good reflectors of electromagnetic energy transmitted through a void (as in non-contact microwave sensors). But with the guided technique the same mechanical constraints exist that cause problems for the capacitance (RF) techniques mentioned previously by having a probe in the vessel.
Spin wave
Spin waves are observed through four experimental methods: inelastic neutron scattering, inelastic light scattering (Brillouin scattering, Raman scattering and inelastic X-ray scattering), inelastic electron scattering (spin-resolved electron energy loss spectroscopy), and spin-wave resonance (ferromagnetic resonance). In the first method the energy loss of a beam of neutrons that excite a magnon is measured, typically as a function of scattering vector (or equivalently momentum transfer), temperature and external magnetic field. Inelastic neutron scattering measurements can determine the dispersion curve for magnons just as they can for phonons. Important inelastic neutron scattering facilities are present at the ISIS neutron source in Oxfordshire, UK, the Institut Laue-Langevin in Grenoble, France, the High Flux Isotope Reactor at Oak Ridge National Laboratory in Tennessee, USA, and at the National Institute of Standards and Technology in Maryland, USA. Brillouin scattering similarly measures the energy loss of photons (usually at a convenient visible wavelength) reflected from or transmitted through a magnetic material. Brillouin spectroscopy is similar to the more widely known Raman scattering but probes a lower energy and has a superior energy resolution in order to be able to detect the meV energy of magnons. Ferromagnetic (or antiferromagnetic) resonance instead measures the absorption of microwaves, incident on a magnetic material, by spin waves, typically as a function of angle, temperature and applied field. Ferromagnetic resonance is a convenient laboratory method for determining the effect of magnetocrystalline anisotropy on the dispersion of spin waves. Very recently, one group at the Max Planck Institute of Microstructure Physics in Halle, Germany proved that by using spin polarized electron energy loss spectroscopy (SPEELS), very high energy surface magnons can be excited. This technique allows people for the first time to probe the dispersion of magnons in the ultrathin ferromagnetic films. The first experiment was performed for a 5 ML Fe film. With momentum resolution, the magnon dispersion was explored for an 8 ML fcc Co film on Cu(001) and an 8 ML hcp Co on W(110), respectively. The maximum magnon energy at the border of the surface Brillouin zone was 240 meV.
Sound
In human physiology and psychology, sound is the "reception" of such waves and their "perception" by the brain. Humans can only hear sound waves as distinct pitches when the frequency lies between about 20 Hz and 20 kHz. Sound waves above 20 kHz are known as ultrasound and is not perceptible by humans. Sound waves below 20 Hz are known as infrasound. Different animal species have varying hearing ranges.
Traumatic brain injury modeling
Blast-Induced TBI results from wave propagation from a blast source through the brain. These injuries are most commonly found on the battlefield, as explosions occur close enough to humans that the high intensity waves apply stresses and strains that greatly surpass neuron elastic thresholds. As the wave passes through the skull, cerebrospinal fluid, and through the brain, neurons undergo sequences of tension and compression for the duration of the blast wave. Even very short blast waves with high intensity can cause immediate cell death, even through the cerebrospinal fluid buffer. Blast-Induced damage is not localized to a specific region due to its wave nature, and can penetrate deep into the brain before finally subsiding, depending on the blast intensity and proximity.
NeuroSky
The human brain is made up of billions of interconnected neurons; the patterns of interaction between these neurons are represented as thoughts and emotional states. Every interaction between neurons creates a minuscule electrical discharge; alone these charges are impossible to measure from outside the skull. However, the activity created by hundreds of thousands concurrent discharges aggregates into waves which can be measured.
Gamma wave
As mentioned above, gamma waves have been observed in Tibetan Buddhist monks. A 2004 study took eight long-term Tibetan Buddhist practitioners of meditation and, using electrodes, monitored the patterns of electrical activity produced by their brains as they meditated. The researchers compared the brain activity of the monks to a group of novice meditators (the study had these subjects meditate an hour a day for one week prior to empirical observation). In a normal meditative state, both groups were shown to have similar brain activity. However, when the monks were told to generate an objective feeling of compassion during meditation, their brain activity began to fire in a rhythmic, coherent manner, suggesting neuronal structures were firing in harmony. This was observed at a frequency of 25–40 Hz, the rhythm of gamma waves. These gamma-band oscillations in the monk’s brain signals were the largest seen in humans (apart from those in states such as seizures). Conversely, these gamma-band oscillations were scant in novice meditators. Though, a number of rhythmic signals did appear to strengthen in beginner meditators with further experience in the exercise, implying that the aptitude for one to produce gamma-band rhythm is trainable.
Microwave auditory effect
Auditory sensations of clicking or buzzing have been reported by some workers at modern day microwave transmitting sites that emit pulsed microwave radiation. Auditory response to transmitted frequencies from approximately 200 MHz to at least 3 GHz has been reported. The cause is thought to be thermoelastic expansion of portions of auditory apparatus, and the generally accepted mechanism is rapid (but minuscule, in the range of 10 °C) heating of brain by each pulse, and the resulting pressure wave traveling through the skull to the cochlea.
Topographic map (neuroanatomy)
The auditory system is the sensory system for hearing in which the brain interprets information from the frequency of sound waves, yielding the perception of tones. Sound waves enter the ear through the auditory canal. These waves arrive at the eardrum where the properties of the waves are transduced into vibrations. The vibrations travel through the bones of the inner ear to the cochlea. In the cochlea, the vibrations are transduced into electrical information through the firing of hair cells in the organ of Corti. The organ of Corti projects in an orderly fashion to structures in the brainstem (namely, the cochlear nuclei and the inferior colliculus), and from there to the medial geniculate nucleus of the thalamus and the primary auditory cortex. Adjacent sites on the organ of Corti, which are themselves selective for the sound frequency, are represented by adjacent neurons in the aforementioned CNS structures. This projection pattern has been termed tonotopy.
Sensory neuroscience
A typical experiment in sensory neuroscience involves the presentation of a series of relevant stimuli to an experimental subject while the subject's brain is being monitored. This monitoring can be accomplished by noninvasive means such as functional magnetic resonance imaging (fMRI) or electroencephalography (EEG), or by more invasive means such as electrophysiology, the use of electrodes to record the electrical activity of single neurons or groups of neurons. fMRI measures changes in blood flow which related to the level of neural activity and provides low spatial and temporal resolution, but does provide data from the whole brain. In contrast,
Electrophysiology provides very high temporal resolution (the shapes of single spikes can be resolved) and data can be obtained from single cells. This is important since computations are performed within the dendrites of individual neurons.
Alpha wave
Following this lapse-of-attention line of thought, a recent study indicates that alpha waves may be used to predict mistakes. In it, MEGs measured increases of up to 25% in alpha brain wave activity before mistakes occurred. This study used common sense: alpha waves indicate idleness, and mistakes are often made when a person is doing something automatically, or "on auto-pilot", and not paying attention to the task they are performing. After the mistake was noticed by the subject, there was a decrease in alpha waves as the subject began paying more attention. This study hopes to promote the use of wireless EEG technology on employees in high-risk fields, such as air traffic controlling, to monitor alpha wave activity and gauge the attention level of the employee.
Brainwave entrainment
Brainwave entrainment, also referred to as brainwave synchronization and neural entrainment, refers to the hypothesized capacity of the brain to naturally synchronize its brainwave frequencies with the rhythm of periodic external stimuli, most commonly auditory, visual, or tactile.
Brain activity and meditation
Many studies on mindfulness meditation, assessed in a review by Cahn and Polich in 2006, have linked lower frequency alpha waves, as well as theta waves, to meditation. Much older studies report more specific findings, such as decreased alpha blocking and increased frontal lobe specific theta activity. Alpha blocking is a phenomenon where the active brain, normally presenting beta wave activity, cannot as easily switch to alpha wave activity often involved in memory recall. These findings would suggest that in a meditative state a person is more relaxed but maintains a sharp awareness. Two large, recent comprehensive review works, however, point to poor control and statistical analyses in these early studies and comment that it can only be said with confidence that increased alpha and theta wave activity exists.
Functional magnetic resonance imaging (fMRI) is another highly utilized methodology for studying state changes in meditating brains. fMRI detects subtle increases in blood flow to areas of the brain with higher metabolic activity. Thus these areas of increased metabolic activity indicate which regions of the brain are currently being used to process whatever stimuli presented. Counter to EEG, the advantage of fMRI is its spatial resolution, with the ability to produce detailed spatial maps of brain activity. It suffers, however, in temporal resolution and cannot measure progressive activity, like the EEG, with much detail.
Amplitude of low frequency fluctuations
Amplitude of Low Frequency Fluctuations (ALFF) and fractional Amplitude of Low Frequency Fluctuations (f/ALFF) are neuroimaging methods used to measure spontaneous fluctuations in BOLD-fMRI signal intensity for a given region in the resting brain. Whole-brain ALFF shows greater signal in posterior cingulate, precuneus, and medial prefrontal areas of the default mode network, but also in non-cortical areas near the ventricles, cisterns and large blood vessels. f/ALFF reduces the sensitivity of ALFF to physiological noise by taking the ratio of each frequency (0.01-0.08 Hz) to the total frequency range (0-0.25 Hz). Both measures have been investigated as part of reliable biomarkers for many neurological conditions including schizophrenia, and ADHD.
Thought identification
In 2013 a project led by University of California Berkeley professor John Chuang published findings on the feasibility of brainwave-based computer authentication as a substitute for passwords. Improvements in the use of biometrics for computer authentication has continually improved since the 1980s, but this research team was looking for a method faster and less intrusive than today's retina scans, fingerprinting, and voice recognition. The technology chosen to improve security measures is an electroencephalogram (EEG), or brainwave measurer, to improve passwords into "pass thoughts." Using this method Chuang and his team were able to customize tasks and their authentication thresholds to the point where they were able to reduce error rates under 1%, significantly better than other recent methods. In order to better attract users to this new form of security the team is still researching mental tasks that are enjoyable for the user to perform while having their brainwaves identified. In the future this method could be as cheap, accessible, and straightforward as thought itself.
Inner ear
The human ear has evolved with two basic tools to encode sound waves; each are separate in detecting high and low frequency sounds. Georg von Békésy (1899-1972) employed the use of a microscope in order to examine the basilar membrane located within the inner-ear of cadavers. He found that movement of the basilar membrane resembles that of a traveling wave; the shape of which varies based on the frequency of the pitch. In low frequency sounds, the tip (apex) of the membrane moves the most, while in high frequency sounds, the base of the membrane moves most.
Sensorimotor rhythm
The sensorimotor rhythm (SMR) is a brain wave. It is an oscillatory idle rhythm of synchronized electric brain activity. It appears in spindles in recordings of EEG, MEG, and ECoG over the sensorimotor cortex. For most individuals, the frequency of the SMR is in the range of 13 to 15 Hz.
Microwave auditory effect
In 1975, an article by neuropsychologist Don Justesen discussing radiation effects on human perceptions referred to an experiment by Joseph Sharp and Mark Grove at the Walter Reed Army Institute of Research during which Sharp and Grove reportedly were able to recognize nine out of ten words transmitted by "voice modulated microwaves". Since the radiation levels approached the (then current) 10 mW/cm² limit of safe exposure, critics have observed that under such conditions brain damage from thermal effects of high power microwave radiation would occur, and there was "no conclusive evidence for MAE at lower energy densities".
Sharp waves and ripples
Sharp waves and ripples (SWRs) are oscillatory patterns in the mammalian brain hippocampus seen on an EEG during immobility and sleep. There are three major network oscillation patterns in the hippocampus: theta waves, SWRs and gamma waves. Gamma oscillations are found in all major brain structures, whereas theta and sharp waves are specific to the hippocampus and its neighbouring areas. SWRs are composed of large amplitude sharp waves in local field potential and associated fast field oscillations known as ripples. SWRs are shown to be involved in memory consolidation and the replay of wakefulness-acquired memory. These network oscillations are the most synchronous patterns in the brain, making them susceptible to pathological patterns such as epilepsy.
Sensory gating
Electroencephalography (EEG) and magnetoencephalographies (MEG) are used to measure brain responses and are common techniques for studying sensory gating. One type of EEG measure used for sensory gating research is the event-related potential (ERP). EEG research on sensory gating shows that gating starts almost immediately after receiving a stimulus. Positron emission tomography (PET) studies have shown that an increased need to gate information is accompanied by increased engagement of the thalamus. P50 wave testing is one of many auditory event-related potential studies.
Beta wave
Beta waves were discovered and named by the German psychiatrist Hans Berger, who invented electroencephalography (EEG) in 1924, as a method of recording electrical brain activity from the human scalp. Berger termed the larger amplitude, slower frequency waves that appeared over the posterior scalp when the subject's eye were closed alpha waves. The smaller amplitude, faster frequency waves that replaced alpha waves when the subject opened his or her eyes were then termed beta waves.
Altered state of consciousness
Altered states of consciousness can be assessed by observations and imaging of the brain such as functional magnetic resonance imaging (fMRI), computed tomography scan (CT), magnetic resonance imaging (MRI) or electroencephalography (EEG) which records the electrical brain wave activity. Imaging is most important to make a diagnosis when patient's history is unobtainable and the physical examination is not dependable. (Dandan, 2004)
Earl K. Miller
Miller has innovated techniques for recording from many neurons simultaneously in multiple brain areas. This is a departure from the classic single-neuron recording approach. It allows detailed and direct comparison of neuron properties between brain areas that are not confounded by extraneous factors and examination of the temporal dynamics of activity between neurons. Miller's lab has used this approach to make a number of discoveries of how different brain areas collaborate to produce thought and action. This includes recent discoveries that oscillating "brain waves" may control the timing of shifts of attention and that different items simultaneously held in short-term memory line up on different phases of each brain wave. The latter may explain why we can only think about a few things at the same time.
Alpha wave
Alpha waves are neural oscillations in the frequency range of 8–12 Hz arising from the synchronous and coherent (in phase or constructive) electrical activity of thalamic pacemaker cells in humans. They are also called Berger's waves after the founder of EEG.
MRI sequence
Functional MRI (fMRI) measures signal changes in the brain that are due to changing neural activity. It is used to understand how different parts of the brain respond to external stimuli or passive activity in a resting state, and has applications in behavioral and cognitive research, and in planning neurosurgery of eloquent brain areas. Researchers use statistical methods to construct a 3-D parametric map of the brain indicating the regions of the cortex that demonstrate a significant change in activity in response to the task. Compared to anatomical T1W imaging, the brain is scanned at lower spatial resolution but at a higher temporal resolution (typically once every 2–3 seconds). Increases in neural activity cause changes in the MR signal via "T" changes; this mechanism is referred to as the BOLD (blood-oxygen-level dependent) effect. Increased neural activity causes an increased demand for oxygen, and the vascular system actually overcompensates for this, increasing the amount of oxygenated hemoglobin relative to deoxygenated hemoglobin. Because deoxygenated hemoglobin attenuates the MR signal, the vascular response leads to a signal increase that is related to the neural activity. The precise nature of the relationship between neural activity and the BOLD signal is a subject of current research. The BOLD effect also allows for the generation of high resolution 3D maps of the venous vasculature within neural tissue.
Metastability in the brain
Noise at the "1/f" regime can be found in many biological systems – for instance, in the output of a heartbeat in an ECG waveform—but serves a unique purpose for phase synchrony in neuronal networks. At the "1/f" regime, the brain is in the critical state necessary for a conscious response to weak or chaotic environmental signals because it can shift the random signals into identifiable and predictable oscillatory waveforms. While often transient, these waveforms exist in a stable form long enough to contribute to what can be thought of as conscious response to environmental stimuli.
F wave
In neuroscience, an F wave is the second of two voltage changes observed after electrical stimulation is applied to the skin surface above the distal region of a nerve. F waves are often used to measure nerve conduction velocity, and are particularly useful for evaluating conduction problems in the proximal region of nerves (i.e., portions of nerves near the spinal cord).
Brainwave entrainment
Entrainment is a concept first identified by the Dutch physicist Christiaan Huygens in 1665 who discovered the phenomenon during an experiment with pendulum clocks: He set them each in motion and found that when he returned the next day, the sway of their pendulums had all synchronized.
Mu wave
The mu wave is of interest to a variety of scholars. Scientists who study neural development are interested in the details of the development of the mu wave in infancy and childhood and its role in learning. Since a group of researchers believe that autism spectrum disorder (ASD) is strongly influenced by an altered mirror neuron system and that mu wave suppression is a downstream indication of mirror neuron activity, many of these scientists have kindled a more popular interest in investigating the mu wave in people with ASD. Assorted investigators are also in the process of using mu waves to develop a new technology: the brain-computer interface (BCI). With the emergence of BCI systems, clinicians hope to give the severely physically disabled population new methods of communication and a means to manipulate and navigate their environments.
Stimulus modality
The human ear is able to detect differences in pitch through the movement of auditory hair cells found on the basilar membrane. High frequency sounds will stimulate the auditory hair cells at the base of the basilar membrane while medium frequency sounds cause vibrations of auditory hair cells located at the middle of the basilar membrane. For frequencies that are lower than 200 Hz, the tip of the basilar membrane vibrates in sync with the sound waves. In turn, neurons are fired at the same rate as the vibrations. The brain is able to measure the vibrations and is then aware of any low frequency pitches.
Psychology
A classic and popular tool used to relate mental and neural activity is the electroencephalogram (EEG), a technique using amplified electrodes on a person's scalp to measure voltage changes in different parts of the brain. Hans Berger, the first researcher to use EEG on an unopened skull, quickly found that brains exhibit signature "brain waves": electric oscillations which correspond to different states of consciousness. Researchers subsequently refined statistical methods for synthesizing the electrode data, and identified unique brain wave patterns such as the delta wave observed during non-REM sleep.
Brainwave entrainment
It is widely accepted that patterns of neural firing, measured in Hz, correspond with states of alertness such as focused attention, deep sleep, etc.It is hypothesized that listening to these beats of certain frequencies one can induce a desired state of consciousness that corresponds with specific neural activity.
Trance
There are four principal brainwave states that range from high-amplitude, low-frequency delta to low-amplitude, high-frequency beta. These states range from deep dreamless sleep to a state of high arousal. These four brainwave states are common throughout humans. All levels of brainwaves exist in everyone at all times, even though one is foregrounded depending on the activity level. When a person is in an aroused state and exhibiting a beta brainwave pattern, their brain also exhibits a component of alpha, theta and delta, even though only a trace may be present.
Neuroimaging
Magnetoencephalography (MEG) is an imaging technique used to measure the magnetic fields produced by electrical activity in the brain via extremely sensitive devices such as superconducting quantum interference devices (SQUIDs) or spin exchange relaxation-free (SERF) magnetometers. MEG offers a very direct measurement of neural electrical activity (compared to fMRI for example) with very high temporal resolution but relatively low spatial resolution. The advantage of measuring the magnetic fields produced by neural activity is that they are likely to be less distorted by surrounding tissue (particularly the skull and scalp) compared to the electric fields measured by electroencephalography (EEG). Specifically, it can be shown that magnetic fields produced by electrical activity are not affected by the surrounding head tissue, when the head is modeled as a set of concentric spherical shells, each being an isotropic homogeneous conductor. Real heads are non-spherical and have largely anisotropic conductivities (particularly white matter and skull). While skull anisotropy has a negligible effect on MEG (unlike EEG), white matter anisotropy strongly affects MEG measurements for radial and deep sources. Note, however, that the skull was assumed to be uniformly anisotropic in this study, which is not true for a real head: the absolute and relative thicknesses of diploë and tables layers vary among and within the skull bones. This makes it likely that MEG is also affected by the skull anisotropy, although probably not to the same degree as EEG.
Alpha wave
Alpha waves again gained recognition in the early 1960s and 1970s with the creation of a biofeedback theory relating to brain waves (see below). Such biofeedback, referred to as a kind of neurofeedback, relating to alpha waves is the conscious elicitation of alpha brainwaves by a subject. Two researchers in the United States explored this concept through unrelated experiments. Joe Kamiya, of the University of Chicago, discovered that some individuals had the conscious ability to recognize when they were creating alpha waves, and could increase their alpha activity. These individuals were motivated through a reward system from Kamiya. The second progenitor of biofeedback is Barry Sterman, from the University of California, Los Angeles. He was working with monitoring brain waves in cats and found that, when the cats were trained to withhold motor movement, they released SMR, or mu, waves, a wave similar to alpha waves. Using a reward system, he further trained these cats to enter this state more easily. Later, he was approached by the United States Air Force to test the effects of a jet fuel that was known to cause seizures in humans. Sterman tested the effects of this fuel on the previously-trained cats, and discovered that they had a higher resistance to seizures than non-trained cats.
Collaborative Study on the Genetics of Alcoholism
The brain wave is called an event-related potential (ERP) and is similar to an EEG. Brainwaves are monitored in a non-invasive procedure that involves placing a cap on the subject's head, similar to a bathing cap. This cap will monitor the brain's natural electrical activity and will record the brain's response when the subject is presented with various stimuli. Subjects respond to computer programs on a screen in front of them that flash various stimuli on the screen.
Richard Caton
On 4 August 1875 Caton reported to the British Medical Association in Edinburgh that he had used a galvanometer to observe electrical impulses from the surfaces of living brains in the rabbit and monkey.. After Caton died, Hans Berger was one of few to recognise his importance and cited him in his 1929 report on the discovery of Alpha waves. He wrote:Caton has already published experiments on the brains of dogs and apes in which bare unipolar electrodes were placed either on the cerebral cortex and the other on the surface of the skull. The currents were measured by a sensitive galvanometer. There were found distinct variations in current, which increased during sleep and with the onset of death strengthened, and after death became weaker and then completely disappeared. — "Translated by Cohen, 1959." .Caton wrote a number of clinical papers for the British Medical Association, which arose from observations during his clinical practice. He wrote on such diverse topics as intestinal antisepsis, acromegaly, rheumatic endocarditis, cardiac dilatation and hypertrophy. He also developed his interest in the classics, giving a lecture to the Royal Institution, London, in 1898 on the topic of the excavations carried out by Europeon and American archaeologists who deciphered inscriptions and restored buildings such as the Temple of Asklepios at Epidauros. In 1904, he gave his first Harveian lecture to the Royal College of Physicians on the topic of early Egyptian medicine.
Beta wave
Beta wave, or beta rhythm, is a neural oscillation (brainwave) in the brain with a frequency range of between 12.5 and 30 Hz (12.5 to 30 cycles per second). Beta waves can be split into three sections: Low Beta Waves (12.5–16 Hz, "Beta 1 power"); Beta Waves (16.5–20 Hz, "Beta 2 power"); and High Beta Waves (20.5–28 Hz, "Beta 3 power"). Beta states are the states associated with normal waking consciousness.
NeuroSky
Different brain states are the result of different patterns of neural interaction. These patterns lead to waves characterized by different amplitudes and frequencies; for example waves between 12 and 30 hertz, Beta Waves, are associated with concentration while waves between 8 and 12 hertz, Alpha Waves, are associated with relaxation and a state of mental calm. (The contraction of muscles is also associated with unique wave patterns, isolating these patterns is how some NeuroSky devices detect blinks.)
A-weighting
The curves were originally defined for use at different average sound levels, but A-weighting, though originally intended only for the measurement of low-level sounds (around 40 phon), is now commonly used for the measurement of environmental noise and industrial noise, as well as when assessing potential hearing damage and other noise health effects at all sound levels; indeed, the use of A-frequency-weighting is now mandated for all these measurements, because decades of field experience have shown a very good correlation with occupational deafness in the frequency range of human speech. It is also used when measuring low-level noise in audio equipment, especially in the United States. In Britain, Europe and many other parts of the world, broadcasters and audio engineers more often use the ITU-R 468 noise weighting, which was developed in the 1960s based on research by the BBC and other organizations. This research showed that our ears respond differently to random noise, and the equal-loudness curves on which the A, B and C weightings were based are really only valid for pure single tones.
Cerebellopontine angle syndrome
The auditory brainstem response (ABR) test gives information about the inner ear (cochlea) and nerve pathways for hearing via ongoing electrical activity in the brain measured by electrodes placed on the scalp. Five different waves (I to V) are measured for each ear. Each waveform represents specific anatomical points along the auditory neural pathway. Delays of one side relative to the other suggest a lesion in cranial nerve VIII between the ear and brainstem or in the brainstem itself. The most reliable indicator for acoustic neuromas from the ABR is the interaural latency differences in wave V: the latency in the impaired ear is prolonged. Different studies have indicated the sensitivity of ABR for detection of acoustic neuromas 1cm or larger to be between 90 and 95%. Sensitivity for neuromas smaller than 1cm are 63-77%. A newer technology, stacked ABR, may have sensitivity as high as 95% with specificity 88% for smaller tumors. ABR is considerably more cost effective, but MRI provides more information.
Hallowell Davis
During the 1930s, Davis participated in the development of electroencephalography and was the first person in the United States to have his brain waves scanned by an EEG device. He focused on the physiology of the inner ear, investigating how neurological impulses are transmitted to the brain via the cochlear nerve. His studies led to the development of electrical-response audiometry, which allowed diagnosis of hearing difficulties in infants. Robert Galambos credited Davis with coining the word "audiology" in the 1940s, with Davis saying the then-prevalent term "auricular training" sounded like a method of teaching people how to wiggle their ears.
Mu wave
Mu waves have been studied since the 1930s, and are referred to as the wicket rhythm because the rounded EEG waves resemble croquet wickets. In 1950, Henri Gastaut and his coworkers reported desynchronization of these waves not only during active movements of their subjects, but also while the subjects observed actions executed by someone else. These results were later confirmed by additional research groups, including a study using subdural electrode grids in epileptic patients. The latter study showed mu suppression while the patients observed moving body parts in somatic areas of the cortex that corresponded to the body part moved by the actor. Further studies have shown that the mu waves can also be desynchronized by imagining actions and by passively viewing point-light biological motion.
Omegawave
The most comprehensive of their products, Omegawave Team, takes measurements relevant to an athletes physiological condition, including ECG, Omega (DC potential of the brain), neuromuscular, and reaction rate measurements, for analysis by their cloud-service. Measurements and their results can be taken for a whole team and viewed by a coach locally, or remotely via the company’s cloud-service. They also have a related product for individual athletes called Omegawave Personal.
Brainwave entrainment
Neural oscillations are rhythmic or repetitive electrochemical activity in the brain and central nervous system. Such oscillations can be characterized by their frequency, amplitude and phase. Neural tissue can generate oscillatory activity driven by mechanisms within individual neurons, as well as by interactions between them. They may also adjust frequency to synchronize with the periodic vibration of external acoustic or visual stimuli.
Omegawave
It is from the Omega measurement that the company takes its name. DC potentials of the brain are sometimes called Omega-potential and the measurement of them is sometimes called Omegametry.
First observation of gravitational waves
In the present approach used by LIGO, a laser beam is split and the two halves are recombined after travelling different paths. Changes to the length of the paths or the time taken for the two split beams, caused by the effect of passing gravitational waves, to reach the point where they recombine are revealed as "beats". Such a technique is extremely sensitive to tiny changes in the distance or time taken to traverse the two paths. In theory, an interferometer with arms about 4 km long would be capable of revealing the change of space-time – a tiny fraction of the size of a single proton – as a gravitational wave of sufficient strength passed through Earth from elsewhere. This effect would be perceptible only to other interferometers of a similar size, such as the Virgo, GEO 600 and planned KAGRA and INDIGO detectors. In practice at least two interferometers would be needed, because any gravitational wave would be detected at both of these but other kinds of disturbance would generally not be present at both, allowing the sought-after signal to be distinguished from noise. This project was eventually founded in 1992 as the Laser Interferometer Gravitational-Wave Observatory (LIGO). The original instruments were upgraded between 2010 and 2015 (to Advanced LIGO), giving an increase of around 10 times their original sensitivity.
Electroencephalography
The brain's electrical charge is maintained by billions of neurons. Neurons are electrically charged (or "polarized") by membrane transport proteins that pump ions across their membranes. Neurons are constantly exchanging ions with the extracellular milieu, for example to maintain resting potential and to propagate action potentials. Ions of similar charge repel each other, and when many ions are pushed out of many neurons at the same time, they can push their neighbours, who push their neighbours, and so on, in a wave. This process is known as volume conduction. When the wave of ions reaches the electrodes on the scalp, they can push or pull electrons on the metal in the electrodes. Since metal conducts the push and pull of electrons easily, the difference in push or pull voltages between any two electrodes can be measured by a voltmeter. Recording these voltages over time gives us the EEG.
Fetal EEG
To record the most accurate brain signals, scientists try to minimize the distance between the recording electrode and fetal cortex by using an ultrasound to get the electrodes on the maternal abdomen as close to the fetal head as possible. The original fetal EEGs came from recordings through the maternal abdomen. However, electrical activity from the mother’s heart, abdominal and uterine muscles all create artifacts in the fetal EEG recording. An artifact is electrical activity detected by the EEG that comes a source that the scientist does not want to measure. Muscles create electrical activity in the range of 20–100 Hz, and the uterine wall creates slow-wave activity and fast-wave activity related to the intrauterine pressure. Furthermore, the maternal heartbeat dominates recordings in every electrode and must be filtered out with computer algorithms.
Microwave auditory effect
Numerous individuals suffering from auditory hallucinations, delusional disorders, or other mental illnesses have claimed that government agents use forms of mind control technologies based on microwave signals to transmit sounds and thoughts into their heads as a form of electronic harassment, referring to the alleged technology as "voice to skull" or "V2K".
Unihemispheric slow-wave sleep
Unihemispheric slow-wave sleep (USWS) is sleep with one half of the brain while the other half remains alert. This is in contrast to normal sleep where both eyes are shut and both halves of the brain show reduced consciousness. In USWS, also known as asymmetric slow-wave sleep, one half of the brain is in deep sleep, a form of non-rapid eye movement sleep and the eye corresponding to this half is closed while the other eye remains open. When examined by low-voltage electroencephalography (EEG), the characteristic slow-wave sleep tracings are seen from one side while the other side shows a characteristic tracing of wakefulness. The phenomenon has been observed in a number of terrestrial, aquatic and avian species.
Auditory brainstem response
The auditory brainstem response (ABR) is an auditory evoked potential extracted from ongoing electrical activity in the brain and recorded via electrodes placed on the scalp. The measured recording is a series of six to seven vertex positive waves of which I through V are evaluated. These waves, labeled with Roman numerals in "Jewett" and "Williston" convention, occur in the first 10 milliseconds after onset of an auditory stimulus. The ABR is considered an "exogenous response" because it is dependent upon external factors.
Stimulus modality
Otoacoustic emissions test (OAE) and auditory brainstem response (ABR) testing measures the brain's response to sounds. The OAE measures hearing of newborns by placing an emitting sound into the baby's ear through a probe. A microphone placed in the baby's ear canal will pick up the inner ear's response to sound stimulation and allows for observation. The ABR, also known as the brainstem auditory evoked response (BAER) test or auditory brainstem evoked potential (ABEP) test measure the brain's response to clicking sounds sent through headphones. Electrodes on the scalp and earlobes record a graph of the response.
Acoustocerebrography
Acoustocerebrography (ACG) is a medical test used to diagnose changes and problems in the brain and the central nervous system. It allows for the noninvasive examination of the brain's cellular and molecular structure. It can also be applied as a means to diagnose and monitor intracranial pressure, for example as incorporated into continuous brain monitoring devices. ACG uses molecular acoustics, in audible and ultrasound frequency ranges, to monitor changes. It may use microphones, accelerometers, and multifrequency ultrasonic transducers. It does not use any radiation and is completely free of any side effects. ACG also facilitates blood flow analysis as well as the detection of obstructions in cerebral blood flow (from cerebral embolism) or bleeding (from cerebral hemorrhage).
Biofeedback
An electroencephalograph (EEG) measures the electrical activation of the brain from scalp sites located over the human cortex. The EEG shows the amplitude of electrical activity at each cortical site, the amplitude and relative power of various wave forms at each site, and the degree to which each cortical site fires in conjunction with other cortical sites (coherence and symmetry).
NeuroSky
MindWave: The MindWave is a NeuroSky product released in 2010 in China and 2011 in the US and the EU. It costs $99 US making it one of the least expensive EEG device to ever be produced. The MindWave has been marketed as both an education and entertainment device. The MindWave won the Guinness Book of World Records award for “Heaviest machine moved using a brain control interface”.
Audiology and hearing health professionals in developed and developing countries
ABR is an electrophysiologic measure of the function of cranial nerve eight and the auditory pathway in the brainstem. Three electrodes are placed on the scalp in order to record electrical responses from auditory stimuli. Recordings may be measured when the baby is sleeping, sedated, or in a quiet state. ABR recordings are correlated with the degree of hearing loss, for click ABR this range is from 1k to 4k Hz within 10 to 15 dB HL. The screening version of ABR, or automated ABR (AABR), is designed to produce a simple pass or fail result. AABR has high sensitivity (>90%), high specificity (>96%) and low positive predictive value (19%) (Vohr et al., 2001; Watkin, 2001). One advantage of AABR is that it is able to identify auditory neuropathy; however, the disadvantage is that AABR may miss mild sensorineural or exclusively low frequency hearing loss. Therefore, it is recommended that hearing screening programs utilize a two-stage screening protocol that is made up of TEOAEs and AABR. Combined, these two tests have the most favorable combination of specificity, sensitivity, acceptability and high coverage in hospitals with a wide range of birth rates (Kennedy et al., 2000; Vohr et al., 2001). McPherson and Olusanya (2008) write, "evidence from ongoing infant hearing screening programs has shown that these tests are acceptable to parents because they are not invasive, painless and quick to administer. They are currently employed in developed countries and in a growing number of developing countries." Lastly, it is recommended that the two-stage screening protocol be performed on newborns prior to hospital discharge in order to decrease the number of infants lost to follow-up care.
Expectation fulfilment theory of dreaming
It is known from laboratory studies of brain waves that, just before entering REM sleep and while in it, powerful electrical signals pass through the brain. On electroencephalogram recordings, these appear as spikes and are known as PGO spikes, after the initials of names of the structures of the brain they pass through. These same spikes occur during waking, when attention is drawn to a stimulus, the phenomenon being known as ‘the orientation response’. While sleeping, the spikes appear to represent the cue to dream.
Primal therapy
Janov initiated from the outset small-scale research using questionnaires and measures of EEG, body temperature, blood pressure and pulse from his patients. A 1971 "Pittsburgh Press" article cited a University of California at Irvine study on primal therapy patients that showed a slowing of brain waves. Janov claimed that primal therapy reduced, in some patients, the frequency and the amplitude of Alpha waves, core body temperature (as much as three degrees) and blood pressure (as much as 30 percent). Two Brain Research Institute (UCLA) scientists confirmed that there were brain-wave changes in primal patients.
Acoustocerebrography
All brain tissue is influenced by blood circulating in the brain's vascular system. With each heartbeat, blood circulates in the skull, following a recurring pattern according to the oscillation produced. This oscillation's effect, in turn, depends on the brain's size, form, structure and its vascular system. Thus, every heartbeat stimulates minuscule motion in the brain tissue as well as cerebrospinal fluid and therefore produces minimal changes in intracranial pressure. These changes can be monitored and measured in the skull.
Today, mostly passive sensors like accelerometers are used to identify these signals correctly. Sometimes highly sensitive microphones are utilized.
Steady state topography
Steady State Topography (abbreviated SST) is a methodology for observing and measuring human brain activity that was first described by Richard Silberstein and co-workers in 1990. While SST has been principally used as a cognitive neuroscience research methodology it has also found commercial application in the field of neuromarketing and consumer neuroscience in such areas as brand communication, media research and entertainment. In a typical SST study, brain electrical activity (electroencephalogram or EEG) is recorded while participants view audio visual material and/or perform a psychological task. Simultaneously, a dim sinusoidal visual flicker is presented in the visual periphery. The sinusoidal flicker elicits an oscillatory brain electrical response known as the Steady State Visually Evoked Potential (SSVEP). Task related changes in brain activity in the vicinity of the recording site are then determined from SSVEP measurements at that site. One of the most important features of the SST methodology is the ability to measure variations in the delay (latency) between the stimulus and the SSVEP response over extended periods of time. This offers a unique window into brain function based on neural processing speed as opposed to the more common EEG amplitude indicators of brain activity.
Three specific features of the SST methodology make it a useful technique in cognitive neuroscience research as well as neuroscience-based communication research.
Metastability in the brain
Metastability, a state in which signals (such as oscillatory waves) fall outside their natural equilibrium state but persist for an extended period of time, is a principle that describes the brain’s ability to make sense out of seemingly random environmental cues. In the past 25 years, interest in metastability and the underlying framework of nonlinear dynamics has been fueled by advancements in the methods by which computers model brain activity.
Game brain
Mori performed an experiment at Tokyo's Nihon University designed to measure the effect of video games on human brain activity by examining beta waves, which are produced during Beta states ⁠— the states associated with normal waking consciousness. Mori claims his study has revealed that people who spend long periods playing video games have less activity in the brain's pre-frontal region, which governs emotion and creativity, in contrast to their peers. He claims that the experiment demonstrates the existence of an "adverse effect that video games have on the human brain". Specifically, Mori asserts that side effects can include loss of concentration, an inability to control temper and problems socializing or associating with others. "Game brain" refers to these effects and the state of the brain.
Microwave burn
Pulsed microwave radiation can be perceived by some workers as a phenomenon called "microwave hearing"; the irradiated personnel perceive auditory sensations of clicking or buzzing. The cause is thought to be thermoelastic expansion of portions of auditory apparatus. The auditory system response occurs at least from 200 MHz to at least 3 GHz. In the tests, repetition rate of 50 Hz was used, with pulse width between 10–70 microseconds. The perceived loudness was found to be linked to the peak power density instead of average power density. At 1.245 GHz, the peak power density for perception was below 80 mW/cm. The generally accepted mechanism is rapid (but minuscule, in the range of 10 °C) heating of brain by each pulse, and the resulting pressure wave traveling through skull to cochlea.
Hemi-Sync
Hemi-Sync is a trademarked brand name for a patented process used to create audio patterns containing binaural beats, which are commercialized in the form of audio CDs. Interstate Industries Inc., created by Hemi-Sync founder Robert Monroe, is the owner of the Hemi-Sync technology. 
"Hemi-Sync" is short for "Hemispheric Synchronization," also known as "brainwave synchronization". Monroe claimed that the technique synchronizes the two hemispheres of one's brain, thereby creating a 'frequency-following response' designed to evoke certain effects. Hemi-Sync has been used for many purposes, including relaxation and sleep induction, learning and memory aids, helping those with physical and mental difficulties, and reaching altered states of consciousness through the use of sound.
The technique involves using sound waves to entrain brain waves. Wearing headphones, Monroe claimed that brains respond by producing a third sound (called binaural beats) that encouraged various brainwave activity changes. In 2002, a University of Virginia presentation at the Society for Psychophysiological Research examined Monroe's claim. The presentation demonstrated that EEG changes did not occur when the standard electromagnetic headphones of Monroe's setup were replaced by air conduction headphones, which were connected to a remote transducer by rubber tubes. This suggests that the basis for the entrainment effects is electromagnetic rather than acoustical.
Ilchi Lee
One of the mental and physical health enhancement techniques that Ilchi Lee created, Brain Wave Vibration (head-shaking), was used as a kind of moving meditation in a research study published in the international journal, Neuroscience Letters, in July 2010. Using two psychological questionnaires, this study suggested that regular practitioners of Brain Wave Vibration were less stressed and experienced more positive emotions and fewer psychosomatic symptoms. As well, regular Brain Wave Vibration practitioners had more dopamine in their blood than the healthy control group. The Ministry of Science and Technology of South Korea funded the research. Researchers from several departments of Seoul National University and the university hospital collaborated for the research along with the Korea Institute of Brain Science, of which Ilchi Lee is president.
Neurotechnology
Electroencephalography (EEG) is a method of measuring brainwave activity non-invasively. A number of electrodes are placed around the head and scalp and electrical signals are measured. Typically EEGs are used when dealing with sleep, as there are characteristic wave patterns associated with different stages of sleep. Clinically EEGs are used to study epilepsy as well as stroke and tumor presence in the brain. EEGs are a different method to understand the electrical signaling in the brain during activation.
Resting state fMRI
Functional magnetic resonance imaging (functional MRI or fMRI) is a specific magnetic resonance imaging (MRI) procedure that measures brain activity by detecting associated changes in blood flow. More specifically, brain activity is measured through low frequency BOLD signal in the brain.
Functional magnetic resonance imaging
The primary form of fMRI uses the blood-oxygen-level dependent (BOLD) contrast, discovered by Seiji Ogawa. This is a type of specialized brain and body scan used to map neural activity in the brain or spinal cord of humans or other animals by imaging the change in blood flow (hemodynamic response) related to energy use by brain cells. Since the early 1990s, fMRI has come to dominate brain mapping research because it does not require people to undergo shots nor surgery, to ingest substances, nor to be exposed to ionising radiation. This measure is frequently corrupted by noise from various sources; hence, statistical procedures are used to extract the underlying signal. The resulting brain activation can be graphically represented by color-coding the strength of activation across the brain or the specific region studied. The technique can localize activity to within millimeters but, using standard techniques, no better than within a window of a few seconds. Other methods of obtaining contrast are arterial spin labeling and diffusion MRI. The latter procedure is similar to BOLD fMRI but provides contrast based on the magnitude of diffusion of water molecules in the brain.
Beta wave
Beta waves are often considered indicative of inhibitory cortical transmission mediated by gamma aminobutyric acid (GABA), the principal inhibitory neurotransmitter of the mammalian nervous system. Benzodiazepines, drugs that modulate GABA receptors, induce beta waves in EEG recordings from humans and rats. Spontaneous beta waves are also observed diffusely in scalp EEG recordings from children with duplication 15q11.2-q13.1 syndrome (Dup15q) who have duplications of GABA receptor subunit genes "GABRA5", "GABRB3", and "GABRG3". For this reason, it is possible that, in certain clinical contexts, beta waves could be a general biomarker of GABA receptor gene overexpression or otherwise aberrant GABAergic transmission.
Electroencephalography
EEG has several strong points as a tool for exploring brain activity. EEGs can detect changes over milliseconds, which is excellent considering an action potential takes approximately 0.5–130 milliseconds to propagate across a single neuron, depending on the type of neuron. Other methods of looking at brain activity, such as PET and fMRI have time resolution between seconds and minutes. EEG measures the brain's electrical activity directly, while other methods record changes in blood flow (e.g., SPECT, fMRI) or metabolic activity (e.g., PET, NIRS), which are indirect markers of brain electrical activity. EEG can be used simultaneously with fMRI so that high-temporal-resolution data can be recorded at the same time as high-spatial-resolution data, however, since the data derived from each occurs over a different time course, the data sets do not necessarily represent exactly the same brain activity. There are technical difficulties associated with combining these two modalities, including the need to remove the "MRI gradient artifact" present during MRI acquisition and the ballistocardiographic artifact (resulting from the pulsatile motion of blood and tissue) from the EEG. Furthermore, currents can be induced in moving EEG electrode wires due to the magnetic field of the MRI.