Cerebral Cortex Functional Localization

Abstract

The cerebrum is the largest part of the brain and consists of the cerebral cortex and basal ganglia. The cerebral cortex consists of four lobes: the anteriorly placed frontal lobe, the parietal lobe in the middle, and the occipital lobe posteriorly with the inferiorly placed temporal lobe. The cortical neurons are found on the surface of the cerebrum covering the cortical white matter. Deep in the white matter is found the basal ganglia, which will be discussed in the motor system. I. Anatomical Considerations Cerebral Cortical Gray Matter A firm knowledge of the structure and function of the cerebral cortex and the rela-tionship of the cerebral cortex to the subcortical centers is of crucial importance for all who wish to understand the behavior and accomplishments of humans as opposed to other animal forms. The use of the thumb and fingers for fine manipula-tions with tools, the use of linguistic and mathematical symbols for communication in the auditory and visual spheres, and the capacity for postponement of gratifica-tion all reflect the evolution of the cerebral cortex. The cerebral cortical gray matter consists of 16 billion nerve cells and is organized into a laminar arrangement, with an almost infinite number of synapses. Beaulieu and Colonnier (1966) have estimated that in a cubic millimeter of neocortex there are 2.78 × 10 8 synapses, 84% of which are type I (excitatory) and 16% are type II (inhibitory). The almost infinite number and variety of circuits present not only have provided the ana-tomical substrate for the recording of an infinite number of past experiences but have also allowed for a plasticity of future function projected both in time and in space. The attempt to relate functional differences to the differences in structure of the various areas of the cerebral cortex was a scientific outgrowth of the earlier philosophical argu-ments concerning the relationship of mind and body. We may indicate at the onset that, to a certain degree, cytoarchitectural differences do reflect functional differences: 1. Thickness: evident on simple visual inspection (average thickness is 2.5 mm; motor cortex: 4.5 mm; visual cortex: 1.45–2.0 mm.). The basis for the differences in overall thickness is related to differences in the thickness of the layers.