Download Reward” and “Punishment” Function of the Limbic System

The nervous system
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Dr.Abdul-Aziz Ahmed
THE RETICULAR FORMATION AND DIFFUSE
MODULATORY SYSTEMS
(II) Neurohormonal Control of Brain Activity
Aside from direct control of brain activity by transmission of nerve
signals from the lower brain areas to the cortical regions of the brain,
still another physiologic mechanism is very often used to control brain
activity by secreting excitatory or inhibitory neurotransmitter agents
into the substance of the brain. There are four major diffuse modulatory
systems:
1.The raphe nuclei and the serotonin system,

located in the pons and medulla

its neurons secrete serotonin.

it send fibers into the diencephalon, cerebral cortex, spinal cord.
The serotonin secreted at the spinal cord has the ability to suppress
pain. The serotonin released in the diencephalon and cerebrum plays an
essential role in the control of wakefulness and sleep-wake cycles and to
the control of mood and emotions.
Figure; The raphe nuclei and the serotonin system.
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Dr.Abdul-Aziz Ahmed
2. The noradrenergic neuron system

originates in the locus coeruleus of the pons.

it functions as an “alarm center” that becomes most active when
new environmental stimuli appear.

Noradrenergic neurons are widely distributed throughout the CNS
and mediate an increase in the general state of arousal.
Figure; The noradrenergic neuron system
3.The substantia nigra and the dopamine system.

The substantia nigra lies in the superior mesencephalon.

its neurons pass mainly to the caudate nucleus and putamen.

Other neurons pass to ventral areas of the brain, especially to the
hypothalamus and the limbic system.
The dopamine is believed to act as an inhibitory transmitter in the basal
ganglia, but in other areas of the brain it is possibly excitatory.
Dopaminergic neurons play an important role in the brain’s reward
system. The reward system is short circuited by addictive drugs,
including cocaine, amphetamines, alcohol, nicotine, and opiates, which
all increase dopaminergic transmission in the nucleus accumbens.
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Dr.Abdul-Aziz Ahmed
Figure; Dopaminergic neurons system.
4. The gigantocellular neurons of the reticular excitatory area and the
acetylcholine system.
Fibers from gigantocellular neurons (the giant cells) in the reticular
excitatory area of the pons and mesencephalon divide immediately into
two branches, one passing upward to the higher levels of the brain and
the other passing downward into the spinal cord. The neurohormone
secreted at their terminals is acetylcholine. In most places, the
acetylcholine functions as an excitatory neurotransmitter. Activation of
these acetylcholine neurons leads to an acutely awake and excited
nervous system. Cholinergic neurons in the nucleus basalis of Meynert,
a forebrain structure, are involved in the pathogenesis of Alzheimer’s
disease.
Figure; acetylcholine system..
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Dr.Abdul-Aziz Ahmed
principal causes of unconsciousness or
The neurons in the reticular formation has an important influence on the
degree of wakefulness. Consciousness requires proper functioning of the
reticular activating system and both cerebral hemispheres. Therefore,
the principal causes of unconsciousness or coma are:
1. Lesions that damage the reticular activating system.
2. Diffuse damage to both cerebral hemispheres.
3. Global suppression of the cerebrum and/or reticular activating
system by drugs (e.g., sedative-hypnotics or alcohol) or metabolic
derangements (e.g., anoxia, hypercapnia, hypoglycemia, or hepatic
encephalopathy).
Mood disorders, the main two affective (mood) disorders are
1.major depression
2. bipolar disorder, bipolar disorder is expressed by periods of
depression alternating with bouts of mania. Drugs that enhance the
diffuse serotonergic and noradrenergic modulatory systems are among
the most effective treatments available for mood disorders. For example,
the monoamine oxidase inhibitors (MAOIs) reduce the rate of
norepinephrine and serotonin breakdown, which elevates the levels of
these transmitters in the brain. More recently, serotonin-selective
reuptake inhibitors (SSRIs) such as fluoxetine (e.g., Prozac) have been
developed. The effectiveness of these drugs supports the monoamine
hypothesis that low activity of serotonin and norepinephrine is the basis
of mood disorders.
Schizophrenia. is a group of psychotic disorders characterized by a loss
of the normal perceptions of reality evidenced by delusions,
hallucinations, and disordered speech and behavior. Dopamine
antagonists are effective when used as antipsychotic (neuroleptic) drugs
due to the inhibition of dopamine signaling in the mesocorticolimbic
system. The antipsychotic actions of dopamine antagonists are mediated
by blocking D2-receptors. The use of nonselective dopamine antagonists
inhibits the nigrostriatal dopaminergic system, resulting in adverse
effects that resemble Parkinson’s disease.
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The nervous system
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Dr.Abdul-Aziz Ahmed
The limbic system
The concept of a "limbic system" actually encompasses two levels of
structural and functional organization. The first level consists of the
cortical structures on the most medial edge (the limbus) of the
hemisphere:
 the subcallosal area.
 the cingulate gyrus and the isthmus of the cingulate gyrus.
 the parahippocampal gyrus; and the uncus.
 the hippocampal formation.
The second level includes a variety of subcortical nuclei and tracts
 the septal nuclei and nucleus accumbens
 various nuclei of the hypothalamus
 the nuclei of the amygdaloid complex
 parts of the dorsal thalamus,
 habenular nuclei, ventral tegmental area, and periaqueductal
gray.
The functions of limbic system include:,
 emotion, behavior, motivation,
 long-term memory ( specially in hippocampus).
 Emotional component of learning( specially in amygdale).
 olfaction.
 Associated with pain/pleasure, rage
Emotional life is largely housed in the limbic system, and it has a great
deal to do with the formation of memories.
Reward” and “Punishment” Function of the Limbic System
The limbic structures are concerned with the affective nature of sensory
sensations – that is, whether the sensations are pleasant or unpleasant
or also called reward or punishment or satisfaction or aversion:
I. “Reward” and “Punishment” Function of the Limbic System
1.the major reward centers have been found to be located along the
course of the medial forebrain bundle, especially in the lateral and
ventromedial nuclei of the hypothalamus. Less potent reward centers,
are found in the septum, the amygdale. Stimulation of these areas gives
a sense of reward. When offered the choice of eating some delectable
food, the animal often chooses the electrical stimulation.
2.Punishment Centers
The most potent areas for punishment and escape tendencies have been
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Dr.Abdul-Aziz Ahmed
found in the central gray area surrounding the aqueduct of Sylvius. Less
potent punishment areas are found in the amygdala and hippocampus
Stimulation in these areas causes the animal to show all the signs of
displeasure, fear, terror, pain, punishment, and even sickness. Strong
stimulation of the punishment centers, causes the animal to (1) develop
a defense posture, (2) extend its claws, (3) lift its tail, (4) hiss, (5) spit, (6)
growl, and (7) develop piloerection, wide-open eyes, and dilated pupils.
Furthermore, even the slightest provocation causes an immediate
savage attack. This pattern of behavior that is called rage. Fortunately,
in the normal animal, the rage phenomenon is held in check mainly by
inhibitory signals from the ventromedial nuclei of the hypothalamus.
Importance of Reward or Punishment in Behavior
Almost everything that we do is related in some way to reward and
punishment. If we are doing something that is rewarding, we continue to
do it; if it is punishing, we cease to do it. Therefore, the reward and
punishment centers undoubtedly constitute one of the most important
of all the controllers of our bodily activities, our drives, our aversions,
our motivations. Tranquilizers , such as chlorpromazine, usually inhibits
both the reward and the punishment centers, thereby decreasing the
affective reactivity of the animal.
Importance of Reward or Punishment in Learning and Memory –
Habituation Versus Reinforcement
If the sensory experience does not elicit a sense of either reward or
punishment, repetition of the stimulus over and over leads to almost
complete extinction of the cerebral cortical response, thus the animal
becomes habituated to that specific sensory stimulus and thereafter
ignores it.
If the stimulus does cause either reward or punishment , the cerebral
cortical response becomes progressively more and more intense during
repeated stimulation and the response is said to be reinforced
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Dr.Abdul-Aziz Ahmed
Functions of the Hippocampus
The hippocampus presumably has critical decision-making neuronal
mechanism, determining the importance of the incoming sensory
signals. It has been suggested that the hippocampus provides the drive
that causes translation of short-term memory(verbal and symbolic
thinking type) into long-term memory (consolidation).Thus removal of a
portions of the hippocampi as treatment for epilepsy, lead to
anterograde amnesia. These people can recall most previously learned
memories satisfactorily. They are capable of short-term memory for
seconds up to a minute or two, but their ability to establish memories
lasting longer than a few minutes is either completely or almost
completely abolished.
Functions of the Amygdala
The amygdala is a complex of multiple small nuclei located immediately
beneath the cerebral cortex of the medial anterior pole of each temporal
lobe. The amygdala receives neuronal signals from all portions of the
limbic cortex, as well as from the neocortex of the temporal, parietal,
and occipital lobes—especially from the auditory and visual association
areas. Because of these multiple connections, the amygdala has been
called the “window” through which the limbic system sees the place of
in the world. Stimulating the Amygdala had effect on
(1)arterial pressure, heart rate,
(2) gastrointestinal motility and secretion
(3)pupillary dilation or, rarely, constriction,
(4) piloerection,
(5) secretion of various anterior pituitary hormones, especially the
gonadotropins and adrenocorticotropic hormone.
(6) different types of movements associated with olfaction and eating,
such as licking, chewing, and swallowing.
(7).Finally, excitation of still other portions of the amygdale can cause
sexual activities that include erection, copulatory movements,
ejaculation, ovulation, uterine activity, and premature labor.
Effects of Bilateral Ablation of the Amygdala—The Klüver-Bucy
Syndrome.
Klüver-Bucy syndrome is a rare neurologic disorder that occurs as a
result of bilateral lesions of the amygdale (e.g., herpes encephalitis).
Patients exhibit hypersexuality (lack of social sexual restraint),
hyperorality (strong compulsion to place objects in the mouth), visual
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Dr.Abdul-Aziz Ahmed
agnosia (able to see objects, but unable to identify them), flat affect, and
placidity (able to approach danger without anger or fear).
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The nervous system
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Dr.Abdul-Aziz Ahmed
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