(9/30) LTM: Pt 3. Brain and Consolidation

LTM Memory and the Brain

  • Hippocampus crucial in forming new memoires

  • Medial temporal love (MTL)

    • peririhnal cortex

    • parahippocampal Cortex

    • entorhinal cortex

Medial Temporal Lobe

  • Davachi et. al. (2003)

    • place participants in a brain scanner

      • told to form an image to an associated place

        • ex. word “dirty” → dump, trash can

      • then asked to recognize words mixed with new words 20 hrs larter

    • found → encoding activation in peririhnal cortex predicted later item recognition

      • did not find difference with hippocampus activation

      • possible hippocampus more involved with context with object

  • Other brain regions:

    • parietal lobe: involved with recollection of episodic memories & allocated attention in STM

    • frontal lobe: coordinates info in WM by retrieving various pieces of LTM info and combining it (use of episodic buffer, phonological loop, central exec, etc.)

      • source monitoring: remembering the source of info

      • prospective memory: memory for the future of events

    • Amygdala: formation of emotional memories

    • every experience creates the potential for a new memory, but new memories are fragile & can easily disrupted

Memory Consolidation

  • the process by which new memories are transformed from tjeor fragile state to a more permanent state is resistant to disruption

  • This process occurs at two lvls

    • synaptic consolidation: occurs when the synapses begin to structurally change, happens rapidly over a period of minutes

      • structural changes of one neuron at a time

    • systems consolidation: involved the reorganization of brain circuitry and takes much longer, weeks, months, or even years

      • interconnection of interconnected neurons

  • Changes at the synapse

    • studied via physiology of memory

    • continued experience with a stimulus leads to a sequence of chemical reactions, the synthesis of new proteins, & structural changes at the synapse

      • experiences are represented by the pattern of firing across many neurons

    • AP happens faster each time with structural changes

      • less time btw hyperpolarization

    • Long-term potentiation (LTP): enhanced firing of the neruon after repeated stimulation

  • Standard Model of Consolidation

    • Franklin & Bontempi (2005)

      • new info activates hippocampus & the subcortical areas where info can then be stored

      • then re-exposure causes reactivation where the hippocampus reactivation lessens over time

      • at a certain point of time, the cortical connections strengthens and the hippocampus is no longer need bc the memory is now consolidated

        • hippocampus not active for old, remote memories

      • Evidence as support

        • based on studies of brain injury

          • concussions - often unaware of what happened during and right after accident, as well as what happened right before

          • Graded amnesia: more recent past events are disrupted by trauma but not older memories

            • only able to remember a few sec.-mins. before trauma happened

          • Disruption of consolidation, hippocampus cannot make connects with subcortical areas

  • The Multiple Trace Hypothesis

    • Nadel & Moskovitch (‘97)

      • argues that the hippocampus is involved in the retrieval of remote memories (those that are older and consolidated)

    • Evidence for MTH

      • Giboa et al. (2004)

      • found → hippocampus was active when retrieving recent (newer) memories an remote (when 5 y/o) memories

      • Suggests → hippocampus is important for retrieving new & remote (older/consolidated) BUT it does not mean that the hippocampus is important for retrieving all types of memories

  • Which is true?

    • hippocampus is complex

      • it is not always “on” & responses can change over time

      • It doesn’t respond when episodic memories become semantic memories → occurs when memories are very old

        • semanticization of remote memories:

          • ex: i know my name, but dont remember learning it

      • exact role of the hippocampus in the system consolidation is still debated

Memory Reconsolidation

  • memories are fragile

    • when retrieving old memories, they can become modified and/or forgotten → resulting in reconsolidating, the memory needs to be consolidated again

  • Nader et al. (2000)

    • used classical conditioning to develop fear response in rats

      • trying to disrupt the synaptic change responsible for memory formation

      • medicine disrupted the ability to consolidate

    • Condition 3 showed support for reconsolidation & the fragility of memory

      • have to reconsolidate memory to make it strong again

  • Brunet et al (2008)

    • studied individuals w/ PTSD

    • Pts had their traumatic events described to them and were either givein

      • a drug to prevent the production of stress hormone in amygdala

      • a placebo pill

    • 1 wk later → imagine their trauma

    • Found: individuals given the drug showed lower stress response to reliving the traumatic experience than those in the placebo group

      • lower stress response bc the drug disrupts reconsolidation of traumatic memories