PhD MD MBBS Faculty of Medicine Al Maarefa Colleges of Science & Technology Faculty of Medicine Al Maarefa Colleges of Science & Technology Lecture – 11: Limbic System Nervous System Physiology By Dr. SHAHAB SHAIKH PhD MD MBBS Faculty of Medicine Al Maarefa Colleges of Science & Technology Faculty of Medicine Al Maarefa Colleges of Science & Technology

LIMBIC SYSTEM Limbic System includes a complex set of brain structures located on both sides of the thalamus, at the base of cerebrum: –Amygdala –Hippocampus –Cingulate gyrus –Fornix –Septal area –Portions of hypothalamus, Basal Gangli –Portions of thalamus: Ant Thalamic Nuclei –Nucleus accumbens –parahippocampal gyrus –limbic cortex. –also connected to the prefrontal cortex. 2

LIMBIC SYSTEM

The limbic system operates by influencing the endocrine system and the autonomic nervous system. The limbic system had evolved in early mammals to control fight-or-flight responses and react to both emotionally pleasurable and painful sensations. Functions: –Emotion –Motivation –Behavior –Decision Making –Pleasure Center (Nucleus Accumbens) –Associated with Learning & Memory While it is true that limbic structures are more closely related to emotions, the brain is an integrated whole. 5

Emotions: are a state of feeling ( a pleasant or unpleasant mental state) that results in physical and psychological changes that influence our behavior. Emotional feelings include mood, anger, happiness, fear, etc. and associated physical responses includes laughing, crying etc. 6 LIMBIC SYSTEM Emotion is often the driving force behind motivation, positive or negative. Emotions involve different components, such as subjective experience, cognitive processes, psycho-physiological changes, and expressive behavior.

Cingulate Gyrus Situated in the medial aspect of the cerebral cortex and lies immediately above the corpus callosum. is involved with emotion formation and processing, learning and memory. important role in disorders such as depression and schizophrenia. 7

Amygdala are two almond-shaped groups of nuclei located deep and medially within the temporal lobes of the brain. perform a primary role in the processing of memory, decision- making, and emotional reactions. There are functional differences between the right and left amygdala and also between Male and Female Amygdala. 8 The amygdala plays a pivotal role in triggering a state of fear. They perform primary role in the formation and storage of memories associated with emotional events. E.g. Fear Conditioning. Also involved in memory consolidation - Formation of Long Term Memory.

Amygdala Role in Social behavior: It is hypothesized that larger amygdalae allow for greater emotional intelligence, enabling greater societal integration and cooperation with others. Stimulating the amygdala appears to increase both sexual and aggressive behavior. 9 Amygdala is associated with Anxiety and panic attacks. There is a direct relationship between the activation of the amygdala and the level of anxiety the subject feels. Studies have found that the amygdalae may be responsible for the emotional reactions of PTSD patients.

Amygdala 10 Bilateral ablation of amygdala (Klüwer-Bucy Syndrome): Not afraid of anything Extreme curiosity about everything Forgets rapidly Tendency to place everything in mouth & eating objects Strong sexual drive

Hippocampus Major part of limbic system named after its resemblance to the seahorse. It is located in the medial temporal lobe of the brain bilaterally. Has important role in formation of new memory about experienced events (Episodic Memory). Bilateral hippocampal damage results in Anterograde amnesia and often also retrograde amnesia Believed to have role in spatial memory and navigation. Hippocampal sclerosis is the most commonly visible type of tissue damage in temporal lobe epilepsy 11 In Alzheimer's disease, the hippocampus is one of the first regions of the brain to suffer damage. There is evidence that there is atrophy of the hippocampus more than of other parts of the brain in humans having post-traumatic stress disorder, schizophrenia or severe depression.

Limbic Cortex 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 12

lateral hypothalamus – eating, thirst, general level of activity, rage ventromedial nucleus – satiety, tranquility periventricular nucleus – fear, punishment reactions anterior and posterior hypothalamus – sexual drive Behavioral Functions of the Hypothalamus

Behavior and its Control Reward and punishment caused by the Limbic system are important for behavior. Several limbic structures are concerned with sensory experience – is it pleasant or unpleasant? Reward center located in the lateral and ventromedial hypothalamus, thalamus certain areas, Amygdala Punishment center located in Hypothalamus Thalamus Amygdala and Hippocampus

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Neurotransmitters associated with limbic system Norepinephrine Dopamine Serotonin Many drugs increase dopamine in pleasure pathways in limbic system, therefore, cause intense sensation of pleasure e.g. cocaine blocks re-uptake of dopamine at synapses Amphetamine, used in depression, causes increased release of dopamine from dopamine secreting neurons 16

Clinical Application 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 Symptoms: –Loss of interest –Negative mood –Inability to experience pleasure –Suicidal tendency 17

Clinical Application Dementia Alzheimer disease Amnesias Anxiety Depression etc. 18

References Human physiology by Lauralee Sherwood, 8 th edition Text Book Of Physiology by Guyton & Hall, 11 th edition

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