Memory
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    Memory Memory Presentation Transcript

    • Memory Gateway to Learning
    • Types of Memory
      • Declarative memory = Explicit memory
        • Learning about people, places and things
      • Nondeclarative memory = Implicit memory
        • Memory for skills or behavior
      • Working memory temporary information storage
        • includes several types of information
        • probably from several sites in the brain
      • Spatial memory
        • memory of location
      • Relational memory
        • things that happen at same time get stored together in a manner that ties them together
    • Explicit Memory
      • Learning about people, places and things
        • Can be verbally reported
        • Requires conscious awareness
      • Short-term memory
        • temporary, limited in capacity
        • requires continual rehearsal
      • Long-term memory
      • more permanent, much greater capacity
      • does not require continual rehearsal
      • Consolidation
        • transfer from short-term memory to long-term memory
    • Implicit Memory
      • Procedural memory
      • Memory for skills or behavior
      • Perceptual and motor learning
      • Does not require conscious awareness
    • Major Features of Memory
      • Memory has stages
      • Long term memory is represented in multiple regions of the CNS
      • Implicit and explicit memory involve different neural circuits
        • Explicit requires the temporal lobe
        • Implicit involves the cerebellum, amygdala
    • Memory is Not Unitary
      • Memory is not an “all or none” phenomenon
      • Can be implicit or explicit or a mixture
      • Depends on how the information is stored and recalled
    • Amnesia - Loss of Memory
      • Dissociated amnesia
        • not associated with any other cognitve deficits
      • Retrograde amnesia
        • loss of memory for the time period before a trauma
        • typically is gradational from essentially complete loss just before trauma to less and less complete loss earlier and earlier before trauma
      • Anterograde amnesia
        • inability to form new memories
      • Transient global amnesia
        • sudden, brief onset of anterograde amnesia
      • The different types of amnesia suggest that several mechanisms for memory work together
    • Causes of Amnesia
      • Causes
        • concussion, chronic alcoholism, encephalitis, brain tumor, stroke
      • Transient amnesia
        • Probably caused by interruptions in cerebral blood flow
        • Blows to head, physical stress, cold showers, sex, drugs
        • Clioquinol (anti-diarrheal drug) - no longer on market became famous for causing transient global amnesia in some people
    • Localization of Memory Functions
      • Long thought memory was a function of the whole cerebral cortex
      • We now realize that different types of memory are localized in different regions
      • Engram
        • physical representation or location of a memory
    • Cortical Ablation Studies
      • Karl Lashley – 1920s
      • Tried to localize memory engram to association areas of the neocortex
      • Studied effect of brain lesions on ability to learn a maze in rats
        • As more and more of the rat's cortex was ablated, more and more errors were made
        • ability to learn was progressively impaired
      • Lashley incorrectly concluded that the whole neocortex equally participated in memory
        • now know that the problem was that the lesions were too large
    • Cell Assembly
      • Donald Hebb – 1949
      • The internal representation of an object consists of the cortical cells that are activated by the stimulus
        • Group of simultaneously acting neurons = cell assembly
        • Same neurons are involved in sensation and perception
        • All of these cells are reciprocally interconnected
      • Internal representation of an object remains in short term memory as long as the cell assembly is active
      • If assembly active long enough, consolidation occurs
        • Long term memory
        • Neurons that fire together wire together
        • Activating any cells in the assembly activates the memory
      • Led to neural network model                       
    • Localization of Declarative Memories
      • Studies in macaque monkeys - 
      • Lesions in the inferotemporal cortex (IT) cause loss of memory about previously learned visual discrimination tasks, even though vision itself remains normal
        • Cells in the IT may respond preferentially to a familiar face in a particular orientation
        • Cells in IT may change their response during repeated exposure to an unfamiliar face – learning
      • The IT is involved both in vision and visual memory
    • Human Studies
      • fMRI shows what part of the brain is activated during exposure to various types of objects
        • Bird watchers respond more vigorously to pictures of birds
        • Car buffs respond more vigorously to pictures of cars and responses are in different places
    • The Temporal Lobe
      • Wilder Penfield – 1940’s
      • Electrical stimulation of human temporal lobe
        • Studied patients with epilepsy
        • During surgery for epilepsy, stimulated temporal lobe electrically
      • Some patients reported sensations like hallucinations or vivid memories
        • but the patients had other cortical abnormalities
        • Still, temporal lobe stimulation caused different effects than stimulation of other parts of the neocortex
      • Consistant with seizure “aura”
    • Kluver-Bucy Syndrome
      • Researchers at U. Chicago in the 1930’s
      • Studying emotion circuitry
      • Bilateral temporal lobectomy in rhesus monkeys
      • Produces bizarre behavioral abnormnalities
      • One of these is “psychic blindness”
        • Although they could see, could not recognize or understand the meaning of common objects
        • Thus loss of declarative memory
      • More on this phenomenon with emotion
    • Building on Penfield
      • Brenda Milner – 1950’s
        • Studied patients with surgical interventions to treat epilepsy
        • Bilateral removal of the hippocampus and neighboring regions of the temporal lobe
      • Most famous case was “H.M.”
    • Patient “H.M.” Sheds New Light
      • Bilateral removal of mid-temporal lobe
      • Stopped seizures
      • Short term memory was OK
      • Memories formed prior to surgery were OK
      • Ability to form new, long term memories was lost
        • Couldn’t transfer information from short term to long term memory!
      • Similar findings in all bilateral temporal lobe surgical patients
    • Impact on Learning
      • All of the things these patients could recall have an automatic quality
        • Do not require conscious recall
        • Do not require complex cognitive skills such as comparison
      • If the patient practices a puzzle, they improve their ability to solve it, but they don’t remember how.
    • Medial Temporal Lobe Anatomy
      • Hippocampus
        • deep in the medial temporal lobe
      • Entorhinal cortex, perirhinal cortex, parahippocampal cortex
        • Three cortical regions ventral to the hippocampus
        • all involved in memory functions
    • Function of the Medial Temporal Lobe
      • Lesions in monkeys impair discrimination memory
        • ability to recognize whether object has been seen before
      • Lesions impair declarative memory, not procedural memory
      • Lesions impair long-term memory storage, but short-term memory seems to be normal
      • This region seems to be involved in packaging short-term memory for relay to the rest of the neocortex for long-term storage
    • The Diencephalon & Memory
      • Outside of the temporal lobe, one of the regions most associated with memory
      • Axons from the hippocampus project to the mammillary bodies which project to the thalamus
      • Thalamus also receives input from temporal lobe structures including the amygdala & IT
      • Large midline thalamic lesions in monkeys produce severe deficits in ability to learn a matching task
      • Lesions which impact fewer nuclei produce smaller deficits
    • The Diencephalon
      • Three regions have been implicated in memory processing:
        • Anterior nucleus of thalamus
        • Dorsomedial nucleus of thalamus
        • Mammillary bodies in hypothalamus
      • The thalamus & mammillary bodies receive nerve fibers from the medial temporal lobe
    • The Case of “N.A.”
      • Accidentally stabbed with a fencing foil
        • Through his right nostril into his brain
      • Produced a lesion in his left dorsomedial thalamus
      • Cognitive ability normal but memory impaired
      • Caused moderate retrograde amnesia (for the 2 years prior) and profound anterograde amnesia similar to the more extensive damage to H. M.
      • Short term memory and preservation of old memories was intact
      • Suggests that both the temporal lobe and parts of the thalamus may be involved in the formation of long-term declarative memories
    • Korsakoff's Syndrome
      • Usually due to chronic alcoholism
      • Results from alcohol associated thiamin deficiency
      • Produces confusion, severe memory impairment, apathy
      • First presents as abnormal eye movements, loss of coordination, tremors
        • Can be treated in early stages
      • Untreated thiamin defiency leads to brain damage which produces Korsokoff’s
        • Lesions in dorsomedial thalamus and mammillary bodies
      • Anterograde and severe retrograde amnesia
      • Further supports role of diencephalon in memory
    • Anterograde & Retrograde Amnesia
      • While often found together, may have different causes
      • The degree of severity of the two does not correlate in Korsokoff’s
      • Suggests different mechanisms involved
      • Damage to the dorsomedial thalamus and mammillary bodies probably causes anterograde amnesia
      • What causes retrograde amnesia is still unclear
    • Working Memory & the Hippocampus
      • Hippocampus is involved in memory function for a diverse range of tasks
      • Studies of hippocampal ablation in rats
      • Studied “working memory”
      • Used a radial maze containing food
        • Normal rats learn to visit each arm only once
        • If only some arms are used, they learn only to go down those arms, and then only once.
    • The Maze Study
      • Rats with hippocampal lesions still find the food, but they aren't very efficient, going down the same arm repeatedly
      • Rats with lesions can learn to avoid the arms that never have food, but they still explore the food containing arms inefficiently and repeatedly
      • Inability to use changing information
    • Place Cells in the Hippocampus
      • Neurons in the hippocampus selectively respond when rat is in a particular location.
      • If vision is used to determine place, (like landmarks) cell fires in response to where the animal thinks he is
      • May be responsible for learning radial arm maze
      • More than spatial memory is involved
      • Hippocampus may control relational memory
    • Relational Memory
      • Highly processed sensory information comes into the hippocampus & cortex
      • Processing occurs leading to the storage of memories
      • All things happening at the same time are stored together
      • Thus, remembering one thing brings back related memories
      • It's easier to remember events that you had strong feelings about.
      • Spatial navigation is based on a spatial map & relational memories
    • Striatum and Procedural Memory
      • Procedural memory = memory involved in forming behavioral habits
      • Striatum is the major structure involved in procedural memory
      • Striatum may be involved in forming 'habits' in rats, humans, & non-human primates
      • Data from humans suggests that the striatum is involved in a procedural memory system that is separate and distinct from the medial temporal system used for declarative memory
    • Neocortex and Working Memory
      • Humans have much more prefrontal cortex than any other animals
      • Pathways:
        • Medial temporal lobe >> hypothalamus >> anterior nucleus of thalamus >> cingulate cortex
        • Medial temporal lobe >> dorsomedial nucleus of thalamus >> frontal cortex
      • Experiments suggest that frontal cortex is involved with working memory for problem solving and planning of behavior
    • Frontal Lobe & Memory
      • The left frontal lobe (colored regions at left) supports our ability to retrieve the meaning of words and objects.
    • Lateral Intraparietal Cortex (LIP)
      • Cortex buried in intraparietal sulcus
      • Involved in working memory
      • Responses specific to vision
      • Example: monkey looks at fixation point while a stimulus is flashed in periphery; after delay, monkey moves eyes to where the stimulus was
      • Cells in LIP seem to store information about where the eyes are to be moved
        • they remain active during the delay - specific for visual working memory
      • There is a different area specific for auditory working memory
    • Many Structures are Involved in Memory
    • Summary – Memory Pathway #1
      • Visual information is first routed through the thalamus to the visual area of the cerebral cortex.
      • This neural activity is the basis for the sensory register
    • Summary – Memory Pathway #2
      • Information is relayed to the frontal lobes where it is held in short term memory
    • Summary – Memory Pathway #3
      • Information that is stored in long-term memory is held in the hippocampus for weeks or months, and then transferred to the area of the cerebral cortex near where it was originally process for long-term storage
    • Summary – Memory Pathway #4
      • When we recall information from long term memory, it is routed again to the frontal lobes, where it is held in short-term, or “working” memory.