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Chapter 24: Memory Systems

Neuroscience: Exploring the Brain, 4e. Chapter 24: Memory Systems. Introduction. Learning and memory: lifelong brain adaptation to environment Several similarities between experience-dependent brain development and learning

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Chapter 24: Memory Systems

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  1. Neuroscience: Exploring the Brain, 4e Chapter 24: Memory Systems ..

  2. Introduction • Learning and memory: lifelong brain adaptation to environment • Several similarities between experience-dependent brain development and learning • Similar mechanisms at different times and in different cortical areas • Memories range from stated facts to ingrained motor patterns. • Anatomy: several memory systems • Evident from effects of brain lesions

  3. Types of Memory and Amnesia • Learning: acquisition of new information • Memory: retention of learned information • Declarative memory (explicit) • Facts and events • Nondeclarative memory (implicit) • Procedural memory—motor skills, habits

  4. Types of Declarative and NondeclarativeMemory

  5. Types of Procedural Memory • A type of nondeclarative memory • Involves learning a motor response (procedure) • In reaction to sensory input • Occurs in two categories of learning • Nonassociative learning • Associative learning

  6. Types of Nonassociative Learning (a) Habituation (b) Sensitization

  7. Associative Learning • Behavior altered by formation of associations between events • In contrast to changed response to a single stimulus • Classical conditioning (Pavlov) • Pairing of unconditional stimulus with conditional stimulus • Instrumental conditioning (Thorndike) • Associate a response with a meaningful stimulus

  8. Classical Conditioning

  9. Types of Declarative Memory • Working memory • Temporary storage, lasting seconds • Short-term memories—vulnerable to disruption • Facts and events stored in short-term memory • Subset are converted to long-term memories. • Long-term memories • Recalled months or years later • Memory consolidation: process of converting short- to long-term memories

  10. Memory Consolidation

  11. Amnesia • Amnesia: serious loss of memory and/or ability to learn • Causes: concussion, chronic alcoholism, encephalitis, brain tumor, stroke • Limited amnesia (common)—caused by trauma • Dissociated amnesia: no other cognitive deficits (rare) • Retrograde amnesia: memory loss for things prior to brain trauma • Anterograde amnesia: inability to form new memories after brain trauma

  12. Amnesia Produced by Trauma to the Brain

  13. Amnesia—(cont.) • Transient global amnesia • Sudden onset of anterograde amnesia • Also inability to recall the recent past • Lasts a shorter period, from temporary ischemia (e.g., severe blow to head) • Symptoms: disoriented, ask same questions repeatedly; attacks subside in couple of hours; permanent memory gap

  14. Working Memory • We pay attention to small fraction of sensory information. • Some sensory information held briefly in working memory. • Small capacity—limited resource • Mostly discarded, some may be converted to long-term memory • A capability of neocortex found in numerous brain locations

  15. Prefrontal Cortex and Working Memory • Primates have a large frontal lobe. • Functions of prefrontal cortex: self-awareness, capacity for planning and problem solving

  16. Wisconsin Card-Sorting Test • To demonstrate problems associated with prefrontal cortical damage

  17. Working Memory Activity in Monkey Prefrontal Cortex Prefrontal cortex

  18. Imaging Working Memory in the Human Brain • Numerous brain areas in prefrontal cortex involved in working memory. • PET study: Six frontal lobe areas show sustained activity correlated with working memory. • Identity task • Location task • Unknown whether working memory for other types of information is held in same or different brain areas

  19. Human Brain Activity in Two Working Memory Tasks Blue; identity Green; both Red; location

  20. Area LIP and Working Memory • Cortical areas outside frontal lobe also involved in working memory. • Lateral intraparietal cortex (area LIP) • Involved in guiding eye movements • Stimulation causes saccades. • Demonstrated in delayed-saccade task in monkeys • Other modality—specific areas of parietal and temporal cortex have analogous working memory responses

  21. LIP Neuron Response in Delayed-Saccade Task

  22. The Neocortex and Declarative Memory • Lashley’s rat experiments • Cortical lesions produce memory deficits. • Speculated all cortical areas contribute equally (equipotential) • Equipotential capacity later disproved • But memory engrams can be widely distributed in the brain

  23. Hebb and the Cell Assembly • External events are represented in cortical cells. • Cells reciprocally interconnected  reverberation • Simultaneously active neurons—cell assembly • Consolidation by “growth process” • “Fire together, wire together” • Hebb on the engram • Widely distributed among linked cells in the assembly • Could involve neurons involved in sensation and perception

  24. Hebb’s Cell Assembly and Memory Storage

  25. The Medial Temporal Lobes • Important for consolidation and storage of declarative memories • Demonstrated by: • Electrical stimulation in the temporal lobe • Neural recordings from the temporal lobe

  26. Medial Temporal Lobes and Declarative Memory

  27. Information Flow through Medial Temporal Lobe

  28. Electrical Stimulation of the Human Temporal Lobes • Temporal lobe stimulation • Effects different from stimulation of other areas of neocortex • Penfield’s experiments • Stimulation  sensations like hallucinations or recalling past experiences • Temporal lobe: apparent role in memory storage • Caveat: complex sensations reported by minority of patients, all with abnormal brains (epilepsy)

  29. Human Neural Recordings from the Medial Temporal Lobe • Neurons found that preferentially respond to categories • Faces, household objects, outdoor scenes • Invariant neurons—respond to variety of images are structurally or conceptually related • Individual neurons respond selectively to one person’s face. • Many questions remain.

  30. A patient’s hippocampal neuron selectively responds to actress Halle Berry

  31. The Effects of Temporal Lobectomy (H.M.)

  32. Temporal Lobectomy and Amnesia (H.M.) • Removal of temporal lobes had no effect on perception, intelligence, personality. • Anterograde amnesia so profound he could not perform basic human activities (and partial retrograde amnesia) • He could not recognize the doctor who studied him for nearly 50 years. • Impaired declarative memory, but spared procedural memory (mirror drawing) • Normal working memory, morality, IQ • Poor imagination

  33. An Animal Model of Human Amnesia • Studies of macaque medial temporal lobe using experimental ablation • Delayed match-to-sample and delayed non-match to sample (DNMS) tests • Recognition memory tasks • Amygdala and hippocampus not significantly involved in recognition memory • Much still unknown about specific brain areas • Collectively, medial temporal structures critical for consolidation of memory

  34. Delayed Non-Match to Sample (DNMS) Task • Medial temporal lobe structures shown important for memory consolidation

  35. Effect of Medial Temporal Lobe Lesions on DNMS Performance

  36. The Diencephalon and Memory Processing

  37. The Diencephalon and Memory Processing: The Case of N.A. • Radar technician accidentally stabbed through left dorsomedial thalamus • Less severe amnesia, but like H.M.: anterograde and some retrograde amnesia • Korsakoff’s syndrome: chronic alcoholism—thiamin deficiency • Symptoms: confusion, confabulations, severe memory impairment, apathy • Can lead to lesions in dorsomedial thalamus and mammillary bodies • Suggests mechanisms involved in consolidation distinct from processes that recall memories

  38. Memory Functions of the Hippocampal System • Memory formation, retention, retrieval involve system of interconnected brain areas • Hippocampus involved in various memory functions • Binds sensory information for memory consolidation • Supports spatial memory of location of objects of behavioral importance • Involved in storage of memories for some length of time

  39. Effects of Hippocampal Lesions in Rats (a) Normal rats go down each maze arm for food only once - but not with hippocampal lesions (b) Normal and lesioned rats learn which arms are baited and avoid the rest

  40. Spatial Memory and Place Cells • Learning Morris water maze requires hippocampus. • Place cells fire when animal is in a specific place. • Place fields dynamic

  41. Place Cells in Humans • PET imaging in human brain related to spatial navigation of a virtual town

  42. Grid Cells • Identified in rodent neural recordings • Inthe entorhinal cortex • Unlike place cells • Respond when animal is at multiple locations that form hexagonal grid • Likely also grid cells in human entorhinal cortex • Place cells, grid cells, and hippocampal neurons showing sensitivity for head direction  brain region highly specialized for spatial navigation

  43. A Rat Place Cell and a Grid Cell

  44. Hippocampal Functions Beyond Spatial Memory • O’Keefe and Nadel: hippocampus specialized for creating spatial map of environment • Apparent important role in spatial memory • Other hippocampal function theories • Important for working memory • Integrates or associates sensory input • Odor discrimination • Hippocampus links different experiences together.

  45. Odor Discrimination Experiment

  46. Consolidating Memories and Retaining Engrams • Declarative memory formation involves system of interconnected brain structures: • Take in sensory information • Make associations between related information • Consolidate learned information • Store engrams for later recall • Components include hippocampus, cortical areas around hippocampus, diencephalon, neocortex, and more.

  47. Two Models of Memory Consolidation • Standard model of memory consolidation • Information from neocortex areas associated with sensory systems sent to medial temporal lobe for processing • Synaptic consolidation, systems consolidation • Multiple trace model of consolidation • Engrams involve neocortex, but even old memories also involve hippocampus. • Multiple memory traces

  48. Reconsolidation • Rat experiments • Reactivating a memory makes it sensitive to change as when first formed (before consolidation) • Reconsolidation: the reactivation effect • Human reconsolidation experiments • Recalling a memory makes it susceptible to change • Hippocampal activity • Profound implications for treatment of stress associated with unpleasant memories

  49. Introducing false memories and erasing bad memories

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