Hypothalamus & Limbic System

Chapter 12 Excluding pages pg263-278

Hypothalamus

Regulates Homeostasis Hunger Thirst Body Temp, Blood Pressure Sex Drives & Behavior Emotions Via Limbic System Pituitary Gland Circadian Rhythms

Neuroanatomy of Hypothalamus

• Know the names of the nuclei on both sections – Periventricular, medial and lateral – Preoptic anterior, middle and posterior

Neural Basis of Emotion

Fear, Anxiety, & Envy& Love, Joy Role of Cingulate Gyrus, Amygdala, Hypothalamus, Hippocampus

Emotions

• Emotional Experience • Emotional Expression • Input from senses • Processed by cerebral cortex • Behavioral output from somatic motor, autonomic and hypothalamus

Theories of Emotion

• James Lange Theory 1884 • Experience emotions IN RESPONSE to physiological changes in our body • Feel sad because we cry NOT cry because we feel sad • The emotion is the physiology

Cannon-Bard Theory

• 1927: Emotional experience can occur independently of emotion expression • Transect animal spinal cord and emotional expression observed. • Removal or damage to somatic sensory system does not diminish emotion experience.

Discrepency for James-Lange

• The same physiological characteristics can occur without the emotion such as in illness fever etc.

• Difference according to Cannon is the activation of the thalamus (hypothalamus) for the emotional response

Limbic Lobe 1878 Paul Broca

• identified medial surface of cerebrum that are different from the rest of cortex—called it border=limbic lobe • Cortex surrounding corpus callosum • Thought to be involved in olfaction

Papez Circuit

• James Papez 1930s identified limbic structures involved in emotion (added the thalamic structures to the limbic lobe) • Cingulate cortex to hippocampus to hypothalamus via the fornix and from hypothalamus to anterior nuclei of thalamus • Neocortex connects to cingulate cortex • Allows one to experience emotion

Limbic System

• Limbic Lobe and Papez Circuit together • This distinguishes human emotions and responses to situations from the stereotypical response of animals due to reflexive systems involving brainstem

Frontal Lobes of Cortex

• Provides Rationale Control of emotional disposition & involved in personality • Injury to frontal lobes causes change in personality • Control of emotions and impulse control • Example of Phineas Gage

Pathologies

• Tumors and injury to areas of the brain lead to emotional changes.

• Damage to cingulate cortex lead to emotional disturbances: fear, depression, irritability

Fear, Agression & Anxiety

Learned Fear, Anxiety & Temporal Lobes and AMYGDALA

Kluver & Bucy Neuroscientist

• Remove bilateral temporal lobes and monkeys cannot experience fear, approach humans other monkeys and dangerous situtations • Cannot recognize objects by vision; called psychic blindness-use mouth to identify objects seen • striking increase in sexual activity

Kluver-Bucy Syndrome

• Humans with temporal lobe lesions show similar behavior as monkeys with temporal lobectomy • Have flattened emotions, don’t feel happy, sad etc

Amygdala

• Neurons at the pole of the temporal lobe below the cortex on the medial side • Greek name for almond shape • Has 3 nuclei, basolateral, corticomedial and central • Afferents from all lobes of neocortex & hippocampus and cingulate gyrus

Input to Amygdala

• Basolateral nuclei receive sensory input (visual, gustatory, auditory and tactile); also projects to cortex for perception of emotion • Corticomedial nuclei receive olfactory inputs • Central nuclei contain output neurons to hypothalamus and periaqueductal grey in brainstem for physiological responses

Damage to Amygdala

• Decreases emotional response • Kluver-Bucy Syndrome=reduced emotionality • Fearlessness • SM human cannot recognize emotional expressions on faces that are fearful, anxious & angry but recognize happy & disgust • Bilateral amygdala removal reduces memory

Electrical Stimulation of Amygdala

• Cause affective rage when basalateral nuclei is stimulated • Corticomedial stimulation reduces aggression

Learned Behaviors

• Require the amygdala and work through 2 pathways. Integrate information from all sensory systems and orchestrate the physiological and physchological response – Ventral amygdofugal pathway – Stria terminalis

Do Not learn Pathway Names

Hypothalamus-brainstem

• Autonomic nuclei in the brainstem receive synaptic input from hypothalamus via – Medial forebrain bundle – Dorsal longitudinal fasciculus

Aggressive Behaviors

• Androgen levels in males can alter aggressive behaviors • Predatory aggression: purpose is getting food, little sympathetic NS activity – Medial hypothalamus • Affective aggresion: purpose is scare off enemies/protection – Lateral hypothalamus

Hypothalamus and Rabies

• Rabies causes excess rage and aggression • Rabies virus damages hypothalamic neurons • Led identification of hypothalamus as critical brain area involved in anger

Electrical Stimulation of Hypothalamus

• Depending on area, animal shows different behaviors • Associated with eating, sniff & eat • Associated with fear or anger • Demonstrates 2 functions of hypothalamus – Metabolic regulation; homeostasis – Coordinated somatic & visceral responses

Serotonin

• Serotonin containing neurons located in Raphe nucleus in brainstem that project via medial forebrain bundle to hypothalamus & other limbic structures • Aggressive mice have decreased serotonin turnover • Drugs that block serotonin release or synthesis cause increase in aggression

Serotonin Receptors

• 14 5HT receptor subtypes • Mice with no (knock-out) gene for 1A and 1B isoform, the type found in Raphe Nucleus are more aggressive & anxious when stressed otherwise act normally • Specific agonist of 1A and 1B reduce anxiety

Memory Systems

Hippocampus

Hippocampus & Relational Memory

• Highly processed information from association cortex areas enter hippocampus • Hippocampus integrates them—ties them together and then output is stored in other cortical areas • Allows you to retrieve all the information about an event

Patients & Syndromes

• HM-mediotemporal lobe • NA--thalamus • Korsakoffs-thalamus & hypothalamus

Amnesia

• Anterograde – Cannot form any new types of memories so always live at time of injury • Retrograde – Cannot recall stored memories for a specific time period

Memory

• Declarative: Explicit – Facts & Events • Easy to form, easy to lose • Medial Temporal Lobe & Thalamus • Non-Declarative: Implicit • Takes repetition, hard to lose – Procedural • Skills & Habits – Striatum – Classical Conditioning • Skeletal Muscles – Cerebellum • Emotional Responses – Amygdala

Conscious Recollection

• Only declarative memories & not non declarative memories

Declarative Memory

• Essential Anatomy – Medial Temporal Lobe – Entorhinal and Perirhinal, Parahippocampal Cx – Hippocampus – Fornix to Mammilary Body of Hypothalamus – Anterior & Dorsomedial Thalamus that project to cingulate cx (limbic system)

HM

• Had bilateral mediotemporal lobes removed due to epilepsy • Removed amygdala, anterior 2/3 of hippocampus, temporal cortex • Had anterograde amnesia • Studied by Brenda Milner • Could learn by procedural memory but had no recollection of having learned task

Squire & Mishkin

• Neuroscientists create an animal model for HM symptoms • Lesioned amygdala, hippocampus and perirhinal cortex in temporal lobe of monkeys and found that they could no longer perform in recognition memory tests • Later showed that perirhinal cortex is most important for new memory; temporary storage? Memory consolidation?

Diencephalon & Memory Processing

• Anterior thalamic nucleus • Dorsal Medial Thalamic nucleus • Mammillary bodies in hypothalamus

Dorsal medial thalamic nucleus

• Receives input from temporal lobe structures including amygdala & inferiortemporal cortex • Projects to all frontal cortex areas

NA

• Air Force technician injured by fencing foil –penetrated the dorsalmedial thalamus • Developed retrograde amnesia of previous 2 years and severe anterograde amnesia • Supports role of thalamus in memory

Lashley

• Lashley: 1920s studied rats in maze after cortical lesions • Found that all cortical areas are involved in memory

Hebb, Lashley student

• suggested CELL ASSEMBLY = all cells that respond to an external stimulus & are reciprocally interconnected • Neurons that fire together, wire together • 1949 Organization of Behavior • Sensory cortex also stores memory • Led to neural networks computer modeling

Circuit using limbic structures

• Hippocampal output axons travel as a bundle, the fornix, to the mammillary bodies of the hypothalamus • Mammillary body axons project to anterior thalamic nucleus

Definitions

• Declarative & NonDeclarative • Long term & Short Term • Procedural & Working • Experience Dependent Brain Development • Anterograde and Retrograde Amnesia

Learning & Memory

• Adaptations of brain circuitry to life experience • Learning = acquisition of new information or knowledge • Memory = retention of learning

Long Term/Short Term Memory

• Long Term: last years but is selective • Short term: last seconds to hours

Memory based on Vision

• Should be found in cortical area involved in vision processing • inferiortemporal cortex: higher order processing of visual information—stores memory of previously seen objects • Allows recognition of visual objects – Remember Kluver-Bucy pyschic blind monkeys

Penfield

• Neurosurgeon in the 1950’s removed epileptic foci after stimulation • Found that stimulation of temporal lobe in awake patients caused halucinations or memory retrieval