SURFACE
ANATOMY OF THE FOREBRAIN: LATERAL VIEW
The convolutions of
the cerebral cortex permit a large expanse of cortex to be compactly folded
into a small volume, an adaptation particularly prominent in primates. Major
dependable landmarks separate the forebrain into lobes; the lateral (sylvian)
fissure separates the temporal lobe below from the parietal and frontal lobes
above, and the central sulcus separates the parietal and frontal lobes from each
other. Several of the named gyri are associated with specific functional
activities, such as the precentral gyrus (motor cortex) and the post-central
gyrus (primary sensory cortex). Some gyri, such as the superior, middle, and
inferior frontal and temporal gyri, serve as anatomical landmarks of the
cerebral cortex. The insula, the fifth lobe of the cerebral cortex, is deep to
the outer cortex and can be seen by opening the lateral
fissure.
CLINICAL POINT
Some functional
characteristics of the cerebral cortex, such as longterm memory and some
cognitive capabilities, cannot be localized easily to a particular gyrus or
region of cortex. However, other functional capabilities are regionally
localized. For example, the inferior frontal gyrus on the left contains the
neuronal machinery for expressive language capabilities; the occipital pole,
particularly along the upper and lower banks of the calcarine fissure, are
specialized for visual processing from the retino-geniculo-calcarine system.
Some very discrete lesions in further processing sites such as vision-related
regions of the temporal lobe can result in specific deficits, such as agnosia
for the recognition of faces or the inability to distinguish animate objects.
This knowledge provides some clues about how feature extraction in sensory
systems might be achieved in neuronal networks.
