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Memory

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Memory

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

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