C h a p t e r 3 4
Organization and Control of Neural Function
843
Irritation or stimulation can result in vivid hallucina-
tions of long-past events.
Occipital Lobe.
The occipital lobe lies posterior to the
temporal and parietal lobes. It contains the primary
visual cortex (area 17), stimulation of which causes
the experience of bright lights called phosphenes in
the visual field. Just superior and inferior is the visual
association cortex (areas 18 and 19), which is required
for gnostic visual function, by which the meaningful-
ness of visual experience, including experiences of color,
motion, depth perception, pattern, form, and location
in space, occurs.
The neocortical areas of the parietal lobe, between
the somatosensory and the visual cortices, have a func-
tion in relating the texture, or “feel,” and location of an
object with its visual image. Between the auditory and
visual association areas, the
parieto
-
occipital region
is
necessary for relating the meaningfulness of a sound and
image to an object or person.
Limbic System.
The medial aspect of the cerebrum is
organized into concentric bands of cortex, the
limbic
system
(from the Latin
limbus
, “border”), which sur-
rounds the connection between the lateral and third
ventricles. The innermost band just above and below
the cut surface of the corpus callosum is folded out of
sight but is a three-layered cortex ending as the hip-
pocampus in the temporal lobe. Just outside the folded
area is a band of transitional cortex, which includes the
cingulate and the parahippocampal gyri (Fig. 34-17).
The limbic lobe has reciprocal connections with the
medial and the intralaminar nuclei of the thalamus,
with the deep nuclei of the cerebrum, and with the
hypothalamus. Overall, this region of the brain is
involved in emotional experience and in the control of
emotion-related behavior. Stimulation of specific areas
in this system can lead to feelings of dread, high anxi-
ety, or exquisite pleasure. It also can result in violent
behaviors, including attack, defense, or explosive and
emotional speech.
Visual
(17)
(18)
(19)
Visual
association
Auditory (41)
Auditory
association
(42, 22)
Frontal
eye field
(part of 8)
Premotor (6) Motor (4)
Somatosensory (3, 1, 2)
Vestibular
Somatosensory
association (5, 7)
Second
somatosensory
Premotor (6)
Supplementary
motor (6,8)
Motor (4)
Somatosensory
(3, 1, 2)
Visual
(17)
(18)
(19)
Visual
association
Somatosensory
association (5, 7)
B
C
Parietal lobe
Parieto-occipital
fissure
Occipital lobe
Transverse
fissure
Central sulcus
Frontal lobe
Lateral sulcus
Temporal
lobe
A
FIGURE 34-16.
Cerebral hemispheres.
(A)
Lateral view of the cerebral hemispheres showing the
frontal, parietal, occipital, and temporal lobes.
(B)
Left lateral view of the motor and sensory areas of
the cerebral cortex.
(C)
Areas of the motor and sensory cortex in a brain that has been sectioned in
the median plane.
