PHYSIOLOGY of LIMBIC SYSTEM By Dr. Mudassar Ali Roomi (MBBS, M.Phil.) Assistant Professor Physiology
Limbic system: (shown in dark pink) Limbic = border Definition: limbic system means the entire neuronal circuitry that controls emotional behavior and motivational drives. It consists of a core of cortical and diencephalic structures found on the medial aspect of each hemisphere. It is often referred to as the emotional nervous system Limbic system is connected to the reticular formation of brainstem through the medial forebrain bundle *** Limbic system consists of: Limbic cortex Associated deep structures
Limbic cortex: Consists of a ring of cortical tissue around the hilus of cerebral hemisphere. Phylogenetically, limbic cortex is the oldest part of the cerebral cortex. It consists of: Orbitofrontal cortex Sub-callosal gyrus Cingulate gyrus Parahippocampal gyrus Uncus
Associated deep structures: Consist of: Septum area Para-olfactory area Epithalamus Anterior thalamic nuclei Hypothalamus Portion of Basal Ganglia Amygdala Hippocampus
Reward and Punishment Function of the Limbic System Reward Centers: 1. lateral and ventromedial nuclei of the hypothalamus. 2. Centres are also found in the septum, the amygdala, certain areas of the thalamus and basal gangia. Punishment Centers: 1. central gray area surrounding the aqueduct of Sylvius in the mesencephalon 2. periventricular zones of the hypothalamus and thalamus. 3. some locations in the amygdala and hippocampus.
Importance of Reward or Punishment in Learning and Memory Habituation Versus Reinforcement
Functions of Limbic System: 1. Olfaction 2. Control of emotions & behavior 3. Control of food intake, water intake & body weight 4. Control of sexual functions 5. Involved in recent memory 6. Body temperature regulation 7. Regulation of osmolarity
Diseases of the Limbic System There are several well known diseases that are disorders of the limbic system. A few are: 1.Schizophrenia 2.Depression
Diseases of the Limbic System SCHIZOPHRENIA Cause: An increased dopamine response in the limbic system results in schizophrenia. Symptoms of schizophrenia are: 1.Loss of touch with reality 2. Auditory hallucinations 3.Decreased ability to concentrate 4.Decreased memory 5.Regress in child-like behavior 6.Altered mood and impulsive behavior 7. Decreased ability to think and reason DEPRESSION Cause: Depression is caused by decreased levels of NE and/or serotonin in the limbic system. Symptoms of depression are: 1.Intense sadness and despair 2.Anxiety 3.Loss of ability to concentrate 4.Pessimism 5.Feelings of low self esteem 6.Insomnia or hypersomnia 7.Increased or decreased appetite 8.Changes in body temperature and endocrine gland function
Has a centers for punishment and reward Involved in olfaction (important in animals) Control of behavior & emotion Control of sexual function In monkeys, bilateral destruction of amygdala KLUVER BUCY SYNDROME Amygdala:
Effects of Bilateral Ablation of the Amygdala The Klüver-Bucy Syndrome 1. Excessive tendency to put objects into mouth (hyperorality) 2. Changes in behavior of animal (psychic blindness) 3. has extreme curiosity about everything 4. Animal becomes tame & placid 5. forgets rapidly (Anterograde amnesia) 6. Change in dietary habits (Herbivorous animal carnivorous) 7. Over-sexuality
Hippocampus
Features and Functions of hippocampus: it is located in the medial temporal lobe, underneath the cortical surface Has a center for punishment Role in control of behavior & emotions On weak electrical stimulation epilepsy-like fit. Fit is accompanied by hallucination (tactile / visual / olfactory / auditory) Probably one of the reasons for this hyperexcitability of the hippocampi is that they have a different type of cortex from that elsewhere in the cerebrum, having only three layers in some of its areas instead of the six layers found elsewhere. In some patients of epilepsy, removal of hippocampus gives benefit. It is our memory consolidation centre.**** Bilateral destruction of hippocampus anterograde amnesia (loss of recent memory)***
Anterograde amnesia (loss of recent memory) Patient is not able to learn new events or skills. Even not able to remember names & faces of person, to whom the patient meet. Old memory remains intact. Hippocampus is involved in recent memory. ***
Alzheimer's disease Pre-senile dementia is the most common form of dementia In Alzheimer's disease, the hippocampus is one of the first regions of the brain to suffer damage As the disease advances, symptoms can include confusion, irritability, aggression, mood swings, trouble with language, and long-term memory loss. reduced synthesis of the neurotransmitter acetylcholine extracellular beta-amyloid (A β ) deposits Neurofibrillary tangles in the axons