Limbic System PDF

The Limbic System: Memory, Emotion, Homeostasis DPT 542 Functional Neuroscience Fall 2024 See Chapter 18 of Blumenfeld  Objectives Understand the main functions of the limbic system Understand and identify the structures and connections involv...

The Limbic System: Memory, Emotion, Homeostasis DPT 542 Functional Neuroscience Fall 2024 See Chapter 18 of Blumenfeld  Objectives Understand the main functions of the limbic system Understand and identify the structures and connections involved in limbic system functions Identify the functional pathways involved in olfaction Identify the functional anatomy of memory Compare and contrast types of memory  Limbic System Paul Broca “La grande lobe limbique” in 1878  Limbic system Limbus in Latin means “border” or “edge” Limbic Cortex forms ring like limbic lobe around the mantle of the cortex (corpus callosum and upper brainstem-diencepahlic junction).  Structures of the limbic system Limbic Cortex  Limbic System Structures - current thinking Cortical regions Hippocampal formation Subcortical Structures & Parahippocampal gyrus Amygdala Olfactory Cortex Hypothalamic nuclei Cingulate Gyrus Including mammillary body Prefrontal Lobe Temporal Lobe Midline Thalamic Nuclei Insular Cortex e.g. medial dorsal (= dorsal medial) Brainstem visceral areas Main efferent bundles e.g. nu raphe, solitary nu, dorsal vagus Fornix (connects hippocamp nu, reticular formation with mammillary body) Mammillothalamic tract Periaqueductal gray (connects mammillary body with thalamus)  Structures of the limbic system Limbic Cortex  Structures of the limbic system Limbic Cortex From: Crossman AR, Neary D. Neuroanatomy: An Illustrated Colour Text (4th Edition), Elsevier, 2010.  Cingulate Gyrus (ctx) Cingulate Gyrus Cingulum (fiber tract inside of cingulate cortex); projects to and from all neocortical areas and to hippocampus.  Limbic System Structures ID parahippocampal gyrus (hippocampus inside); uncus (amygdala inside); temporal, insular, prefrontal cortices; hypothalamus (mammillary bodies) Olfactory bulb & tract Prefrontal Cortex Uncus Lateral View Ventral View  Functional anatomy H- Homeostasis O- Olfaction M- Memory E- Emotion Functional anatomy limbic system  Basic functional anatomy Olfactory Cortex – smell Hippocampal formation – Memory Amygdala – Emotions and Drives Hypothalamus – Homeostasis  Olfaction Smell contributes to sensation of odors as well as taste Pathway of olfaction – Olfactory receptor neurons – Olfactory Nerves – Olfactory Bulb – Mitral Cells/Tufted Cells – Olfactory Tract – Olfactory Cortex – Anterior Olfactory Nucleus Olfaction  Olfaction Primary olfactory cortex unique Does not receive input from intervening thalamic relay MEMORY From: www.semel.ucla.edu Anatomy of Memory  Hippocampus Formed by infolding of temporal lobe into lateral ventricle Greek for “seahorse”  HIPPOCAMPUS F MD LGN Hippocampal formation= ff D H S S H H= hippocampus proper S=Subiculum D= Dentate gyrus MD = mediodorsal ff=fimbria fornix (axon bundle) Th nu  Papez Circuit Fibers from hippocampal formation Enter Fornix Fibers travel through Fornix and synapse at mammillary bodies Fibers course from mammillary bodies to the thalamus Dr. James Papez (1883-1958) Anatomist Cornell University 1937 Paper “A Proposed Mechanism of Emotion” Structures of the Papez Circuit 2 4 3 1 Papez Circuit Connections  Papez Circuit Hippocampus Fornix Mammillary Body Mammillothalamic tract Anterior Thalamic Nuclei Thalamocingular Tract (Radiation) Internal Capsule Cingulate Gyrus Cingulohippocampal fibers Hippocampus Key: Bold refers to structure Italics refers to pathway  Papez Circuit Establishes a connection between information stored in the unconscious and conscious behavior.  Memory Three types of memory – Declarative (Facts, events, concepts, locations) – Procedural / Nondeclarative (How-To) – Emotional (Feelings)  Declarative Memory Conscious Memory Continues to be studied Explicit Memory Arousal and alertness clearly play a Cognitive Memory role in this conversion. Three Stages Suggestions for aiding in the – Immediate memory (Sensory Register) conversion include writing the Last 1-2 seconds information down utilizing a motor – Short-Term Memory sequence (motor memory?) Brief Storage – events that occurred less than 1 hour previous Loss of information in 1 minute unless continually rehearsed – Long-Term Memory Relatively Permanent Storage Short Term memories consolidated.  Nondeclarative memory Procedural memory Implicit memory Recall of skills and habits. Nonconscious memory Produces changes in performance without conscious awareness. Practice required to store procedural memories – Once skill learned, less attention required while performing task. – Goniometry, Using Sphygmomanometer  Three stages to learn motor skill Cognitive – Beginner trying to understand task and find out what works – Verbally guide movements Associative – Refining movements selected as most effective – Less variation and less dependent on cognition Autonomous – Movements automatic – Multitasking  Emotional memory We know very little about emotional memory  Amygdala Group of nuclei in uncus. – Basolateral group (interconnected with cortex) – Corticomedial group (olfaction) Function: All limbic structures are involved in regulating emotional responses, but especially the amygdala. Via connections with parasympathetic & sympathetic nervous system and endocrine (hormonal) systems, amygdala controls emotional behavior as well as autonomic and endocrine behavioral responses Emotions regulated include fear, rage and sexual behavior.  Functions of Amygdala Determines one’s affective perception of sensory stimuli, particularly stimuli with survival value Interpretation or attachment of meaning to stimuli Memory Provides psychological and physiological responses to stimuli (emotions) Fear and fear conditioning Lesions can lead to diminished capacity for fear – Urbach–Wiethe disease – genetic disorder causing hardening of medial temporal lobe – Symptom: placidity, fearlessness  Amygdala Nuclear complex Means “almond” in Greek Three main nuclei – Corticomedial (Cortical) Olfactory functions – Basolateral Attach emotional significance to stimuli – Central Mediates emotional responses Functions – Emotions and drives – Is involved in all four limbic lobe functions Basolateral nuclei Central nuclei Cortical nuclei  Amygdala and emotions Reciprocal connections between amygdala and hypothalamus/brain stem centers mediate control of HR, peristalsis, sweating, among other changes seen with strong emotions Amygdala attaches emotional significance to memories  Circuits Involved in Emotion and Anxiety heteromodal Primary Primary Assoc. Ctx Sensory Ctx Assoc. Ctx (Limbic) Object Concepts Info Temporal Sensory Features Context Ctx Structures Thalamus Amyg (Limbic) (Limbic) Emotional Stimulus Multiple Outputs to Brainstem Areas Amgydala connectivity Young et al (1994) Rev Neurosci  How does Limbic structures affect Homeostasis? Direct link from limbic structures to the Hypothalamus  Hypothalamus controls and regulates ANS Hypothalamus contains a group of nuclei and connections essential for the regulation of visceral motor, appetitive, emotional and vasomotor activities. Cardiovascular and temperature regulation Respiration Digestion Reproduction Nuclei related to ANS control are heavily connected to the brainstem.  Hypothalamus - endocrine organ releases hormones ◼ Nuclei related to endocrine control are connected through the pituitary gland. ◼ Hypothalamus synthesizes hormones of the posterior pituitary gland and hormonal releasing factors that influence endocrine activity of the anterior pituitary lobe. ◼ The paraventricular and supraoptic nuclei produce posterior pituitary hormones which regulate water metabolism (vasopressin and oxytocin). ◼ Lesions in these nuclei lead to increased thirst and insatiable hunger.  Hypothalamic regulation of behavior ◼ Plays a role in regulating behavior through connections to forebrain structures ◼ Amygdala, hippocampal formation, septal nuclei, cingulate and prefrontal cortices ◼ Recent studies have shown that an enlargement of a group of related hypothalamic nuclei is correlated with addictive behaviors. ◼ Other examples include ◼ Defense behaviors ◼ Foreplay (courtship) which is essential for reproduction  Example: Stress response Hypothalamus, pituitary, Adrenal (HPA) Axis How does Limbic structures affect Homeostasis? Chronic Stress EXAMPLE OF IMPAIRMENT IN MEMORY  Patient H.M. Background Henry Gustav Molaisan 1953 27 year old male with history of epileptic seizures Surgical procedure performed to remove bilateral medial temporal lobes to include the hippocampal formation. MRI post surgery  Patient H.M. post surgery Surgery was effective in reducing seizures Unintended side effects included: – He could remember explicit memories acquired before the surgery e.g., old addresses, normal vocabulary – He COULD NOT form NEW explicit memories e.g., remembering the name of someone he met 30 minutes prior He could not name new world leaders or performers – He could recognize a picture of himself from before his surgery but not from after and doesn’t recognize himself in a mirror  Patient H.M. H.M. has severe explicit / declarative memory disorder H.M. is almost normal on procedural or implicit memory tasks including priming, classical conditioning, and learning motor skills When given the same logical puzzle to solve for several days in a row, H. M. was able to solve the puzzle more quickly each day. This shows that explicit memory depends upon the temporal lobes and implicit does not  Patient H.M. Summary Personality and IQ testing were normal Retained ability to learn tasks that did not require conscious recall Had loss of Declarative Memory – Amnesia – Retrograde amnesia Inability to recall information stored prior to insult – Anterograde amnesia Inability to store new information after an insult Non Declarative Memory remained intact  Memory and the Hippocampus Damage to the hippocampus would result in the inability to form new explicit memories, but the ability to remember the skills of implicit memories questions