Hypothalamus & Limbic System

Chapter 12 Excluding pages pg263-278

Hypothalamus

Regulates HomeostasisHungerThirstBody Temp, Blood PressureSex Drives & BehaviorEmotions Via Limbic SystemPituitary GlandCircadian 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

• Input from senses

• Processed by cerebral cortex

• Emotional Expression

• 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 learnPathway 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