LIMBIC SYSTEM
LECTURE 12
DR.ZAHOOR
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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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Schematic of the Limbic System Components
Location of the Limbic System
Figure 58-4; Guyton & Hall
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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Functions
2. 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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Functions
3. 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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Functions
3. 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
lobe
Functions
- Memory – Short term and Long term memory. If
damage to hippocampus, patient cannot make long
term memory.
- damage causes anterograde amnesia
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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
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.
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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
Functional Areas of the Hypothalamus
Figure 58-6; Guyton & Hall
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)
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THANK YOU
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