Limbic System
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Transcript of Limbic System
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