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