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LIMBIC SYSTEM

LECTURE 12DR.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]

Schematic of the Limbic System Components

Location of the Limbic System

Figure 58-4; Guyton & Hall

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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

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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