Search For The Engram

Lashleys Search for the Engram
1. By strengthening the CS and UCS centre in brain, any excitation of CS flow to UCS evoking UCR
2. the physical representation of what has been learnt
3. If learning depends on new or strengthened connections between two brain areas, knife cut should interrupt and abolish learned response.
  1. Rats on maze and brightness discrimination task, made deep cuts in locations in cerebral cortices
    1. None impaired performances.
      1. Types of learning that he studied didn't depend on connections across cortex
4. Does any portion of the cerebral cortex is more important than others for learning?
  1. Trained rats before or after he removed large portions of the cortex
    1. Lesions impaired performance but deficit depended more on amount of brain damage than its location
      1. Learning and memory apparently didn't rely on a single cortical area
  2. Proposed two principles about nervous system
    1. Equipotentiality
      1. all parts of cortex contribute equally to complex behaviours like learning, and any part of cortex can substitute for any other
    2. mass of action
      1. cortex works as a whole, more cortex is better
5. Another interpretation of findings
  1. Rat finding way to food attends to visual and tactile stimuli, location of body, position of head and other cues.
    1. depends on many cortical areas, but different areas could be contributing in different ways
Modern Search for the Engram
1. Search in cerebellum
2. Thompson & col studied classical conditioning of eyelid responses in rabbits
  1. First tone (CS) then puff of air (UCS) to cornea of rabbits eye
    1. Rabbit blinked at air puff and not tone and later blinked at tone also
      1. recorded activity in various brain cells to find which ones changed their responses during learning
3. Thompson wanted to determine location of learning
  1. A<B<C<D<E<F<
    1. If we damage one of areas, learning will be impaired but can't be sure that learning occurred in the damaged area
4. Thompson identified one nucleus of cerebellum
  1. Lateral Interpositus Nucleus (LIP
    1. At start, little response but as learning proceeded, responses increased
      1. Thompson (1986)
    2. When inv temp suppressed nucleus in an untrained rabbit and presented CS and UCS, no responses shown during training
      1. when LIP recovered, began to learn but learned at the same speed as animals that had received no previous training
        while LIP suppressed, training had no effect
5. INV suppressed activity in red nucleus
  1. midbrain motor area that receives input from the cerebellum
  2. R showed no responses during training
    1. when recovered, R showed strong learned responses to the tone
      1. Temp prevented response but didn't prevent learning
        Learning did not require activity in the red nucleus

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Search For The Engram

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