1 LIMBIC SYSTEM LECTURE 12 DR.ZAHOOR
Dec 16, 2015
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LIMBIC SYSTEM
Limbic System works for 1. Emotion 2. Behavior 3. Motivation 4. Memory (we will discuss in next
lecture).
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LIMBIC SYSTEM
We will study Limbic System under the heading
1) History 2) Functional Anatomy 3) Functions 4) Experiments done in animals 5) Chemical transmitters 6) Clinical applications.
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LIMBIC SYSTEM
1- History - Rhincephlon in RATS was first
identified. Why it was named Rhincephalon? Because Rats are led by Olfactory
stimuli. Than name was changed to LIMBIC
SYSTEM because all animals are not guided by olfactory stimuli.
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WHAT IS LIMBIC SYSTEM?It is ring of Fore brain structures that surround the brain stem
2. Functional Anatomy
Limbic System includes i). Amgdala ii). Hippocampus iii). Cingulate gyrus iv). Portions of hypothalamus v). Portions of thalamus Vi) Portions of basal nuclei vi). Portions of lobes of cerebral cortex [limbic association cortex]
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LIMBIC SYSTEM
Limbic System nuclei are connected by neuron pathway
3. We will discuss the functions of Limbic System
1. Emotion 2. Behavior 3. Motivation
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Functions 1. Emotions
Emotion means feelings, mood, anger, happiness, fear, and physical responses associated with these feeling e.g. laughing, crying
Important – Input processed and giving rise to sensation of FEAR is in Amygdala, it lies in temporal lobe
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Functions2. Behavior
Control of behavior is under the limbic system and higher cortex
e.g. behavior of survival – search for food, attack, socio-sexual behavior response
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Functions3. Motivation
It is well known that person reinforces behavior that has proved gratifying and suppresses that behavior which are associated with unpleasant experience
Areas in limbic system are named as - Reward center - Punishment center
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Functions3. Motivation [cont..]
Why we call reward and punishment center?
Because stimulation in these areas give rise to pleasant and unpleasant sensations
Reward center – are found in regions of behavior activities of eating, drinking
Punishment center – are found in regions of pain
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LIMBIC SYSTEM – Different areas Cingulate Gyrus
Cingulate Gyrus – situated above corpus callosum
Functions - Sociable adaptable - Maternal behavior – care of offspring
( Animal who eat offspring has no cingulate gyrus)
- Emotional behavior Dysfunction causes- Addictions to drugs– seeking pleasure
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LIMBIC SYSTEM AMGDALA
AMGDALA Functions - Sociability – more social, more
friends - Fear response - Pleasure - Post traumatic stress - Aggression - Memory
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LIMBIC SYSTEM Hippocampus
Hippocampus – (Sea horse) Located in Temporal
lobeFunctions - Memory – Short term and Long term memory. If damage to hippocampus, patient cannot make long term memory. - damage causes anterograde amnesia
Hippocampus
FUNCTIONS [CONT..] reward and punishment determine whether or not
information will be stored as memory If no reward or punishment, it is hardly remembered but
a person learns any sensory experience that causes pain or pleasure and makes strong memory trace
hippocampus provides the drive to rehearse and consolidate these sensory experiences
IMPORTANT First area to show damage in ALZEHIMER DISEASE is Hippocampus
Limbic Cortex
FUNCTIONS cerebral association area functions for
control of behavior stimulation of various portions of this
area can elicit almost all types of behavior in an animal
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LIMBIC SYSTEM
HYPOTHALAMUS Major part of Limbic system, it plays
role in - Behavioral control , body
temperature, osmolality of body fluids, control of body weight ( eating and drinking )
- These internal functions are called VEGETATIVE functions of brain and are closely related to Behavior.
Hypothalamus
major output pathway of the limbic system
vegetative functions: neurogenic control of arterial pressure regulation of body temperature regulation of fluid volume regulation of endocrine gland secretion
growth hormone, thyroid hormone, glucocorticoid secretion, sex hormones
Behavioral Functions of the Hypothalamus and Related Areas
lateral hypothalamus eating, thirst, general level of activity, rage
ventromedial nucleus satiety, tranquillity
periventricular nucleus fear, punishment reactions
anterior and posterior hypothalamus sexual drive
Behavior and its Control
Reward and punishment causes the Limbic system so that we can learn. If no reward or punishment we ignore.
Several limbic structures are concerned with sensory experience–is it pleasant or unpleasant? Reward center - the lateral and ventromedial
hypothalamus, thalamus certain areas, Amygdala, Punishment center - located in hypothalamus and
thalamus, Amygdala and Hippocampus Punishment always takes precedent over reward. Punishment can frequently inhibit reward center.
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4. Experiments done in rats
- Experiments done in animals to see behavioral response to Reward and Punishment.
- What was found ? - It was found if electrical stimulus is
rewarding, animal presses the button more often , positive reinforcement.
- But if electrical stimulus causes pain , animal decreases the rate of pressing the bar. So if punishment , we do not do the things again.
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Emotional Behavior
Cerebral cortex plays major role in directing many motor responses during emotional behavior e.g. to do or avoid situation, or modulation, or inhibition of emotional behavior.
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5. NEUROTRANSMITTERS IN PATHWAYS OF EMOTIONS AND BEHAVIOR
These are 1. Norepinephrine 2. Dopamine 3. Serotonin
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NEUROTRANSMITTERS IN PATHWAYS OF EMOTIONS AND BEHAVIOR
Norepinephrine and dopamine are catecholamines, that are present in regions that elicit highest rate of self stimulation –
DO IT YOURSELF
That is why amphatamine [stimulant] is used in depression. It causes increased release of dopamine from dopamine secreting neurons
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OTHER EFFECT OF DOPAMINE
Many drugs increase dopamine in pleasure pathways in limbic system, therefore, cause intense sensation of pleasure e.g. cocaine
Cocaine blocks re-uptake of dopamine at synapses
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6. Clinical Application
Limbic System defects 1- Depression It is psychiatric disorder associated with
defect in limbic system neurotransmitters In depression, neurotransmitter is decreased
which is Norepinephrine or serotonin or both
NOTE – Depression is not neurological disorder i.e.
there is no lesion in the brain
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DEPRESSION
Symptoms in depression are - Loss of interest - Negative mood - Inability to experience pleasure - Suicidal tendency
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TREATMENT FOR DEPRESSION
Anti-depressant drugs are used - Prozac – blocks re-uptake of
released serotonin, therefore, there is increased serotonin at synapses
- Amphetamine – causes increase release of Dopamine .
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Clinical Application
Alzheimer disease Memory loss- recent memory can not
be converted to long term memory ( Ante grade Amnesia)