Lecture 18-Limbic System.pdf

Limbic system Kelly Roballo Emotions…. Memories Leaning Objectives 1. Define and locate the reticular formation 2. Define the Ascending Reticular Activating System (ARAS) 3. Describe the major components of the limbic system. 4. Describe the major afferent and efferent connections and the function...

Limbic system Kelly Roballo Emotions…. Memories Leaning Objectives 1. Define and locate the reticular formation 2. Define the Ascending Reticular Activating System (ARAS) 3. Describe the major components of the limbic system. 4. Describe the major afferent and efferent connections and the function of hippocampus. 5. Describe the major afferent and efferent connections and the function of amygdala. 6. Describe reinforcement functions of the limbic system. Limbic System Main Components Of the Limbic System Limbic Cortex • Unlike the six-layered neocortex, the hippocampal formation has only three layers • Amygdala is a nuclear complex that lies in the anteromedial temporal lobe. It is composed of three main nuclei: corticomedial, basolateral, and central nuclei Overview of the Limbic system Coronal Sections Through Basal Forebrain and Septal Region Coronal Sections Through Basal Forebrain and Septal Region Olfactory System • The primary olfactory cortex receives direct input from secondary sensory neurons without an intervening thalamic relay • The anterior entorhinal cortex receives projections from the piriform cortex • The piriform cortex projects to the orbitofrontal olfactory area both directly and indirectly via relays in the entorhinal cortex, or in the mediodorsal nucleus of the thalamus Central Olfactory Structures On September 1, 1953, time stopped for Henry Molaison • He could remember some things — scenes from his childhood, some facts about his parents, and historical events that occurred before his surgery — but he was unable to form new memories Hippocampal formation • Role in memory and learning • 3 parts: § Dentate gyrus and hippocampus proper are the: archicortex (archicortex is the phylogenetically oldest part of the cerebral cortex) § Subiculum is a transitional zone of cortex between the hippocampus proper and entorhinal area § Parahippocampal gyrus is the neocortex (newest part) Hippocampal Formation 1. Dentate gyrus: The three layers of the dentate gyrus, moving inward from the pia, are the molecular layer, granule cell layer, and polymorphic layer • The principal neurons of the dentate gyrus are granule cells 2. Hippocampus: molecular layer, pyramidal cell layer, and polymorphic layer 3. Subiculum: (same as hippocampus) • The principal neurons of the hippocampus and subiculum are pyramidal cells Hippocampus (“sea horse” in Greek) Major structures of hippocampal circuit Circuit of Papez For the cortical control of emotion & long-term memory storage Circuit of Papez • Hippocampal inputs contain higher-order information from multiple sensorimotor modalities that is processed further by the medial temporal structures for memory storage • memory storage is believed to occur in the association and primary cortices • An important output is the projection from the subiculum to the entorhinal cortex • An additional output pathway is the fornix, which carries outputs to the diencephalon and septal nuclei Hippocampal Input and Output Connections S= subiculum D= dentate gyrus HC= hippocampus EC= entorhinal cortex PRC= perirhinal cortex PHC= perihippocampal cortex Memory Related Structures 1. Medial temporal lobe memory areas: hippocampal formation and adjacent cortex of the parahippocampal gyrus Components of the parahippocampal gyrus Memory Related Structures 2. Medial diencephalic memory areas: thalamic mediodorsal nucleus, anterior nucleus of the thalamus, internal medullary lamina, mamillary bodies, and other diencephalic nuclei lining the third ventricle The basal forebrain may also play a role in memory, primarily through its widespread cholinergic projections to the cerebral cortex Fornix and Medial Diencephalic Memory Pathways n Output fibers from the hippocampal formation form a bundle “fimbria” n Hippocampal commissure provides a route for fibers arising from one hippocampus to reach the contralateral side • The medial temporal lobe memory systems communicate with the association cortex mainly through bidirectional connections via the entorhinal cortex • The medial diencephalic memory systems communicate with the medial temporal memory systems through several systems • Fornix connects the hippocampal formation with the mamillary bodies and septal nuclei, as well as with the anterior thalamic nuclei • Declarative memory involves conscious recollection of facts or experiences • Nondeclarative memory involves nonconscious learning of skills, habits and other acquired behaviors • Amnesia (declarative memory loss) is typical of bilateral medial temporal lobe or bilateral medial diencephalic lesions *Clinical Correlation *Clinical Correlation • Anterograde amnesia is the deficit in forming new memories (from the time of the brain injury) • Cannot learn new address, the date, does not remember any events appeared on news, etc. • Retrograde amnesia is the loss of memories from a period of time before the brain injury • Recent memories for a period of up to several years are dependent on the normal functioning of medial temporal and diencephalic structures *Clinical Correlation Limbic-Hypothalamic Pathways • The subiculum of the hippocampal formation projects to the mamillary bodies via the fornix • Mamillary bodies project via the mamillothalamic tract to the anterior thalamic nucleus, which in turn projects to cingulate gyrus • The amygdala has reciprocal connections with the hypothalamus via stria terminalis and the ventral amygdalofugal pathway The Limbic-Hypothalamic Connections • Important mechanism for emotional influences on autonomic pathways • palms get sweaty and stomach churns when you are anxious • Important for homeostatic pathways, including the immune system • Depressed individuals may be more susceptible to infection Amygdala • Role in behavior and emotions • Associates experiences with consequences and the programs the appropriate behavior. • Animals that uses the sense of smell for behavior (reproduction, food, sense of danger) olfactory sensations are the primary inputs t o the amygdala. Humans is the corticomedial amygdala. • Humans: behavior is nonolfactory experiences (projections from cerebral cortex…friendly, unfriendlily, frightening and dangerous) The Amygdala: Emotions & Drives The Amygdala is a group of nuclei located in the anteromedial temporal lobe Amygdala has three main nuclei 1. Basolateral: connections to diverse cortical areas, basal forebrain, medial thalamus 2. Corticomedial: olfaction, hypothalamus related appetite 3. Central nuclei: autonomic control Cortical Connections of the Amygdala The Amygdala is important for attaching emotional significance to various stimuli perceived by the association cortex Activity in amygdala is important in states of fear, anxiety, and aggression Whereas, activity in the septal area is important in pleasurable states Both side ablation of amygdala causes placid behavior Subcortical Connections of the Amygdala Reciprocal connections between the amygdala and hypothalamic and brainstem centers for autonomic control mediate changes in heart rate, peristalsis, gastric secretion, piloerection, sweating, etc., changes commonly seen with strong emotions Olfactory Connections of the Amygdala Behavioral Functions • Stimulation in the lateral hypothalamus not only causes thirst and eating, but also increases the general level of activity, sometimes leading to overt rage and fighting. • Stimulation in the ventromedial nucleus cause sense of satiety, decreased eating, and tranquility. • Stimulation of a thin zone of periventricular nuclei, located immediately adjacent to the third ventricle usually leads to fear and punishment reactions • Sexual drive can be stimulated from several areas of the hypothalamus, especially the most anterior and most posterior portions of the hypothalamus "Reward" and "Punishment" Function of the Limbic System • (1) Reward Centers are located along the course of the medial forebrain bundle, especially in the lateral and ventromedial nuclei of the hypothalamus • (2) Punishment Centers have been found in the central gray area surrounding the aqueduct of Sylvius in the mesencephalon and extending upward into the periventricular zones of the hypothalamus and thalamus. *Clinical Correlation Korsakoff syndrome or psychosis • is characterized by the loss of recent memory and often a tendency to fabricate accounts of recent events. • This syndrome most often results from chronic alcoholism and associated nutritional deficiency (remember amino acids = neurotransmitters … Ach). • Although the morphology changes have been described in the hippocampus and the mamillary bodies, the most frequent alterations occur in the medial part of the medial dorsal thalamic nuclei *Clinical Correlation Klüver-Bucy syndrome • an absence of emotional response so that fear, rage, and aggression cease to exist. • A compulsion to be overly attentive to all sensory stimuli, to examine all objects visually, tactilely and orally • Hypersexuality • Psychic blindness or visual agnosia, in which objects are not recognized visually • Happen after bilateral removal of the temporal lobes as far posteriorly as the auditory area. *Clinical Correlation