LIMBIC SYSTEM. The hypothalamus & limbic system are intimately concerned with emotional expression and with genesis of emotion.

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1 LIMBIC SYSTEM OBJECTIVES What is limbic system Structures included in limbic system Functions of limbic system Connections of limbic system The Brain and Memory LIMBIC SYSTEM The term limbic system is applied to the part of the brain that consists of a rim of cortical tissue around the hilum of cerebral hemisphere and a group of associated deep structures (amygdala, hippocampus and septal nuclei). The hypothalamus & limbic system are intimately concerned with emotional expression and with genesis of emotion. Emotions have both mental and physical components. THEY INVOLVE : Cognition, an awareness of the sensation and usually its cause. Affect, the feeling of itself Conation, the urge to take action Physical changes, such as sweating, tachycardia and hypertension.

2 The limbic system is a group of forebrain structures that form a border around the upper part of brainstem and corpus callosum on the inner border of cerebrum and the floor of diencephalon, Involved in emotion, motivation, learning and memory. THE LIMBIC SYSTEM The limbic (limbus border) system named for the medial border of the temporal lobe, is a loop of cortical structures surrounding corpus callosum and thalamus.

3 But still some neuroanatomists have argued that the components of this system have so little in common that there is no point to calling it the limbic system. Includes nuclei and tracts along the border between the cerebrum and the diencephalon. Functional grouping rather than anatomical

4 THE STRUCTURES INCLUDED IN THE LIMBIC SYSTEM The limbic system consists of a number of structures: The limbic lobe of cerebrum (consist of 3 gyri that curve along the corpus callosum and medial surface of temporal lobe) is a rim of cerebral cortex on the medial surface of each hemisphere and includes: Cingulate gyrus (cingul belt) lies above the corpus callosum, Parahippocampal gyrus in the temporal lobe below. Hippocampus is a portion of the Para hippocampus gyrus that extends into the floor of lateral ventricle.

5 Dentate gyrus lies b/w hippocampus and parahippocampal gyrus. Amygdala (almond shaped) composed of several groups of neurons located close to the tail of caudate nucleus Thalamic nuclei (anterior and medial) participate in limbic circuits. Mammillary bodies of hypothalamus close to the midline near cerebral peduncles. Septal nuclei within the septal area formed by the regions under corpus callosum and the paraterminal gyrus. The olfactory bulbs. The fornix and other tracts are linked by bundles of interconnecting axon. Hypothalamus, frontal lobe Information flows through the system in what is called the Papez Circuit and loops around and around. THE LIMBIC SYSTEM Refers to several forebrain structures that function together o Cingulate gyrus o Hippocampus o Amygdala o Septal nuclei o Closed circuit of information flow between the limbic system and the thalamus and hypothalamus Information flows through the system in what is called the Papez Circuit and loops around and around. Limbic system and hypothalamus - cooperate in the neural basis of emotional states.

6 Limbic system the center of emotion anger, fear, sexual arousal, pleasure, and sadness. It appears to be primarily responsible for our emotional life, and has a lot to do with the FORMATION OF MEMORIES COMPONENTS OF LIMBIC SYSTEM It includes : Nuclei called the amygdala and hippocampus on the medial side of temporal lobe. A tract called the fornix leading to the mammillary bodies of the hypothalamus, A fold of cortex called cingulate gyrus that arches over the corpus callosum. THE LIMBIC SYSTEM

7 The hippocampus is known as the "emotional brain" because it controls most of the involuntary aspects of emotional behavior related to survival: feelings of pleasure and pain such as anger, fear, and affection. THE BRAIN AND MEMORY The amygdala is an almond-shaped forebrain structure that is part of the limbic system and is involved in emotion and memory. It encodes the emotional qualities associated with particular memories such as fear or anger. THE AMYGDALA It is also involved in encoding memories of sensory stimuli that are associated with rewards and punishment. If damaged or destroyed, the fear response may be impaired or destroyed (ablation). A large projection from the hippocampus goes to the amygdala. Plays a major role in the emotional aspects of memory and learning. Stimulation of this area will cause furious defensive reaction with aggressive noises and gestures. Damage to this area removes fear.

8 THE LIMBIC SYSTEM The prefrontal cortex plays an important role in memory, especially in the ability to remember the order of information The cerebellum is involved in learning motor skills, classical conditioning of simple reflexes, and other procedural memories (movement).

9 FUNCTIONS OF LIMBIC SYSTEM The limbic lobe was formerly called rhinencephalon b/c of its relation to olfaction but only a small part of it is actually concerned with smell. In addition to its role in olfaction, the limbic system is concerned with autonomic responses (changes in BP & respiration) Along with hypothalamus it is also concerned with sexual behavior, the emotions of rage and fear and motivation. FUNCTIONS OF LIMBIC SYSTEM Include: Establishing emotional states. Linking conscious cerebral cortical functions with unconscious functions of the brainstem. Facilitating memory storage and retrieval. Plays a key role in emotions and works with the higher cerebral cortex to control behavioral patterns. Aggression --> lesions of amygdala produce docility, while stimulation results in rage and aggression Fear --> stimulation of amygdala and hypothalamus can produce fear, while ablation (destruction) results in an absence of fear

10 Goal-directed behavior - reward and punishment system- stimulation of certain areas functions as a reward, while stimulation of other areas results in a punishment shock. AFFERENTS & EFFERENTS CONNECTIONS The major connections of limbic system : The fornix connects the hippocampus to the mammillary bodies, which are in turn connected to the anterior nuclei of the thalamus by the mammillothalamic tract. The anterior nuclei of the thalamus project to the cingulate cortex and from there, connections to the hippocampus complete a complex closed circuit. This circuit was originally described by Papez and has been called Papez circuit CONNECTIONS

11 Afferents: o Much of cortex is reciprocally connected to entorhinal cortex o Cholinergic and GABA input via septal nuclei o Amygdala o VTA, LC, Raphe Efferent o Via the fornix o Precommissural: septal nuclei o Post- commissural: mammillary bodies (to anterior thalamic nucleus via mammillothalamic tract)