LIMBIC SYSTEM LECTURE 12 DR.ZAHOOR

LIMBIC SYSTEM Limbic System works for 1. Emotion 2. Behavior 3. Motivation 4. Memory (we will discuss in next lecture).

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.

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.

2. Functional Anatomy 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

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

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

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

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

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

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

LIMBIC SYSTEM AMGDALA AMGDALA Functions - Sociability – more social, more friends - Fear response - Pleasure - Post traumatic stress - Aggression - Memory

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

Hippocampus IMPORTANT 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.

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.

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.

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.

5. NEUROTRANSMITTERS IN PATHWAYS OF EMOTIONS AND BEHAVIOR These are 1. Norepinephrine 2. Dopamine 3. Serotonin

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

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

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

DEPRESSION Symptoms in depression are - Loss of interest - Negative mood - Inability to experience pleasure - Suicidal tendency

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 .

Clinical Application Alzheimer disease Memory loss- recent memory can not be converted to long term memory ( Ante grade Amnesia)

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