PREFRONTAL CORTEX OR ORBITOFRONTAL CORTEX
Prefrontal cortex is the anterior
part of frontal lobe of cerebral cortex, in front of areas 8 and 44. It
occupies the medial, lateral and inferior surfaces and includes orbital gyri,
medial frontal gyrus and the anterior portions of superior, middle and inferior
frontal gyri. Areas present in prefrontal cortex are 9, 10, 11, 12, 13, 14, 23,
24, 29 and 32. Areas 12, 13, 14, 23, 24, 29 and 32 are in medial surface (Table
152.1). Areas 9, 10 and 11 are in lateral surface.
Connections of
Prefrontal Cortex
Afferent
fibers
Afferent
fibers of prefrontal cortex come from:
1. Dorsomedial nucleus of
thalamus
2. Hypothalamus
3. Corpus striatum
4. Amygdala
5. Midbrain.
Areas 23,
24, 29 and 32 receive fibers from anterior nucleus of thalamus. Area 32
receives fibers from suppressor area of precentral cortex also.
Efferent fibers
Efferent
fibers are projected to:
1. Thalamus
2. Hypothalamus
3. Tegmentum
4. Caudate nucleus
5. Pons
6. Temporal lobe of
cerebral cortex.
Area 13, along with
hippocampus, uncus and amygdala sends fibers to mamillary
body of hypothalamus
via fornix. This area is
concerned with emotional reactions.
Functions of
Prefrontal Cortex
Earlier, this area was
considered as inexcitable to electrical stimulation. Hence, it was called the silent
area or association
area. But, now it is known that the stimulation of this area with low
voltage electrical
stimulus causes changes in
the activity of digestive, cardiovascular, respiratory and excretory systems
and other autonomic functions. It also causes fear. Various functions of
prefrontal cortex are:
1. It forms the center for
the higher functions like emotion, learning, memory and social behavior.
Short-term
memories are registered here.
2. It is the center for planned
actions
3. This area is the seat of
intelligence; so, it is also called the organ of mind
4. It is responsible for
the personality of the individuals
5. Prefrontal cortex is
responsible for the various autonomic changes during
emotional conditions,
because of its connections
with hypothalamus and brainstem.
Effect of Lesion of
Prefrontal Cortex
Bilateral lesion or removal
of prefrontal cortex in human beings does not cause paralysis. It causes lack
of
initiation and loss of
mental alertness. Very little or no change occurs in memory, judgment and
intelligence.
APPLIED PHYSIOLOGY –
FRONTAL
LOBE SYNDROME
Injury or ablation of
prefrontal cortex leads to a condition called frontal lobe syndrome.
Features of this syndrome
are:
1. Emotional
instability: There is lack of restraint, leading to hostility, aggressiveness
and restlessness
2. Lack of
concentration and lack of fixing attention
3. There is lack of
initiation and difficulty in planning any
course of action
4. Impairment of recent
memory occurs. However, the memory of remote events is not lost.
5. Loss of moral and
social sense is common and there is loss of love for family and friends
6. There is failure to
realize the seriousness of the condition. The subject has the sense of
well-being
and also has flight of ideas.
7. Apart from mental defects,
there are some functional abnormalities also:
i. Hyperphagia
(increased food intake)
ii. Loss of control over
sphincter of the urinary
bladder or rectum
iii. Disturbances in
orientation
iv. Slight tremor.
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