Fig. 10.2 ). Layer I (molecular layer) has few neuronal cell bodies and contains mostly axon terminals synapsing on apical dendrites. Layer II (external granular layer) contains mostly stellate cells. Layer III (external pyramidal layer) consists mostly of small pyramidal cells. Layer IV (internal granular layer) contains mostly stellate cells and a dense matrix of axons. Layer V (internal pyramidal layer) is dominated by large pyramidal cells, the main source of cortical efferents to most subcortical regions. Layer VI (multiform layer) contains pyramidal, fusiform, and other types of cells.
Most input to the cortex from other regions of the central nervous system (CNS) is relayed by neurons in the thalamus, the paleocortex has four to five layers. The paleocortex is located at the border between the archicortex and neocortex.
In humans, the hippocampal formation is part of the archicortex. It is folded into the temporal lobe and can be viewed only when the brain is dissected. The hippocampal cortex has three layers: the molecular, pyramidal cell, and polymorphic layers. They resemble layers I, V, and VI of the neocortex. The white matter covering the hippocampus is called the alveus, which contains hippocampal afferent and efferent fibers. The efferent axons coalesce to form the fornix (Fig. 10.4
Functions of the Lobes of the Cerebral Cortex
There is no exact correspondence between the folds (lobes and gyri) of the cerebral cortex and function; nevertheless, some with the individual lobes of the cerebral hemispheres have a general association with function that helps clarify cortical organization.
One of the main functions of the frontal lobe is motor behavior. As discussed in , the motor, premotor, cingulate motor, and supplementary motor areas are located •Fig. 10.3 Brodmann’sareasinthehumancerebralcortex.(RedrawnfromCrosbyEC,etal.Correlative Anatomy of the Nervous System. NewYork:Macmillan;1962.)6312578910113825273029262834363523312433321237201919181817B •Fig. 10.4 Thehippocampusandtheamygdalaarelocatedonthemedialaspectofthetemporallobe.Thefornix,themajoroutputpathwayfromthehippocampus,projectstothemammillarybody,whichinturnconnectstotheanteriornucleusofthethalamusviathemammillothalamictract.Alsoillustratedarethecingulategyrus,thebasalforebrainarea(septalnuclei,bednucleusofthestriaterminalis,nucleusaccumbens),andtheprefrontalcortex.(FromPurvesD.Sleepandwakefulness.In:PurvesD,etal[eds].Neuroscience. 3rded.Sunderland,MA:Sinauer;2004.) in the frontal lobe, as is the frontal eye field. These areas are crucial for planning and executing motor behavior. Broca’s area, essential for the generation of speech, is located in the inferior frontal gyrus of the dominant hemisphere for human language (almost always the left hemisphere, as explained later). In addition, the more anterior prefrontal cortex in plays a major role in personality and emotional behavior.
Bilateral lesions of the prefrontal cortex may be produced either by disease or by a surgical frontal lobotomy. Such lesions produce deficits in attention, difficulty in planning and problem solving, and inappropriate social behavior. Aggressive behavior is also lessened and the motivational-affective component of pain is reduced although pain sensation remains. Frontal lobotomies are rarely performed today because modern drug therapies provide more focal and effective management for mental illness and chronic pain.