Learning, Memory and Amnesia: Memory

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  • Created by: meg_lou
  • Created on: 25-04-17 15:53
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  • Memory
    • Interesting Cases
      • KC
        • Motorbike accident resulting in brain damage, including MTL
        • Severe amnesia for personal experiences (episodic)
          • All other cognitive abilities intact e.g. playing card games
      • RB
        • Botched cardiac bypass surgery
        • Suffered cerebral ischemia - disruption of blood supply to the brain
        • Postmortem showed damage to just the CA1 subfield of the hippocampus
          • Hippocampaldamage alone can cause MTLA
    • Neurobiology of Memory
      • Maguire et al. (2000)
        • MRI scans of taxi drivers and controls
        • Correlation between time spent as taxi driver and volume of posterior hippocampus
          • Extensive practice on spatial navigation affects the hippocampus
      • Hippocampus
        • Plays a key role in memory for spatial location
          • Hippocampallesions cause deficits on spatial tasks e.g. Morris water maze
            • Rats placed in murky water learn to swim to a platform below the surface
        • Place cells respond when a subject is in specific location
          • Each place cell has a place field for a part of the environment
            • Fires only when in that environment
        • Grid cells are found in the entorhinal cortex
          • Array of evenly spaced place fields producing a pattern
            • Even spacing of the place fields could provide more information for place cells
      • Cognitive map theory
        • Hippocampus constructs and maintains allocentric maps of the external world from the sensory input it receives
          • Allocentric - representations of space based on relations between external objects
          • Firing of place cells doesn't just depend of spatial location
          • Hippocampaldamage sometimes impairs performance on tasks without spatial component
          • Large and complex so unlikely to have a single function
      • Memory storage
        • Memories stored where in the brain structures involved in its formation
        • Hippocampus - spatial location
        • Perirhinal  cortex - object recognition
        • Mediodorsal nucleus - Korsakoff's symptoms
        • Basal forebrain - AD symptoms
        • Damage to structures results in memory deficits
          • Inferotemporal cortex - visual perception of objects
          • Amygdala - fear learning
          • Prefrontal cortex - working memory
          • Cerebellum - sensorimotor skills, striatum - habit formation
      • Memory consolidation
        • Hebb - memories of experiences stored in the ST by neural activity circulating in closed circuits
          • Studied by administeringECS
            • Length of period of RA produced by it provides an estimate of time needed for consolidation
        • Standard consolidationtheory (Moscovitch et al., 2006)
          • Memories temporarily stored in hippocampusuntil transferred to a more stable cortical storage system
          • Retained memories become more resistant to disruption by hippocampusdamage
            • Each time a similar experience occurs, a new engram is established and linked to the original engram
        • Each time a memory is retrieved from LTM it is held in unstable STM
          • Susceptible to amnesia until it is reconsolidated
    • Synaptic Mechanisms of Learning
      • Long-term potentiation
        • Facilitation of synaptic transmission after high-frequency electrical stimulation to presynaptic neurons
        • Can last many weeks and occurs only if presynaptic firing is followed by postsynaptic firing
        • LTP effects structures in learning and memory
        • Behavioural conditioning can produce LTP like changes in hippocampus
        • LTP can be elicited by low levels of stimulation that mimic normal neural activity
      • 3 part process
        • 1. Induction (learning)
          • Simultaneously, glutamate must bind to NDMA receptor and postsynaptic neuron must be partially depolarised
            • Allow release of calcium ions
        • Maintenance (memory) and expression (recall)
          • Involve changes in both pre and post synaptic neurons

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