Chapter Thirteen The Biology of Learning and Memory

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Chapter ThirteenThe Biology of Learning and
Memory
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Physical Representation of Learning and Memory

• Classical Conditioning-pairing two stimuli
  changes the response to one of them
• Conditioned stimulus-initially elicits no
  response
• Unconditioned stimulus-automatically elicits a
  response
• Unconditioned response-the response brought on by
  the unconditioned stimulus
• Conditioned Response-the response learned to the
  conditioned stimulus

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Figure 13.1  Procedures for classical
conditioning and operant conditioning In
classical conditioning two stimuli (CS and UCS)
are presented at certain times regardless of what
the learner does.
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Operant Conditioning

• Defined-an individuals response is followed by a
  reinforcement or punishment
• Reinforcement-event that increases the future
  probability of the response
• Punishment-event that suppresses the frequency of
  the response

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Figure 13.1  Procedures for classical
conditioning and operant conditioning In operant
conditioning the learners behavior controls the
presentation of reinforcement or punishment.
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Lashleys Engram

• Engram-the physical representation of what has
  been learned
• Trained rats on mazes and observed what happened
  when he disrupted connections between two brain
  areas or removed part of the brain
• Results
• Disrupted connections did not affect maze
  performance
• Maze performance was only decreased when large
  amounts of brain were removed

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Figure 13.3  Cuts that Lashley made in the brains
of various ratsHe found that no cut or
combination of cuts interfered with a rats
memory of a maze.
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Lashleys Conclusions

• Equipotentiality-all parts of the cortex
  contribute equally to complex behaviors like
  learning
• Mass action-the cortex works as a whole, and the
  more cortex the better

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Modern Search for the Engram

• Simple classical conditioning procedures take
  place in the lateral interpositus nucleus
• More complex learning paradigms depend on areas
  outside of the cerebellum

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Short-term and Long-term Memory

• Short-term-events that have just occurred
• Long-term-events from previous times
• Memories that stay in short-term memory long
  enough are consolidated into long-term memory
• Emotional responses can enhance consolidation by
  stimulating the amygdala

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Working Memory

• Defined-the way we store information while
  working with it or attending to it
• Components
• Phonological loop-stores auditory info
• Visuospatial sketchpad-stores visual info
• Central executive-directs attention toward one
  stimulus or another

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Hippocampus and Amnesia

• Anterograde Amnesia-loss of memories for events
  that happen after brain damage
• Retrograde Amnesia-loss of memories that occurred
  shortly before brain damage

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Other Types of Memory

• Declarative-the ability to state a memory in
  words
• Procedural-the development of motor skills
• Explicit-deliberate recall of information that
  one recognizes as a memory
• Implicit-the influence of recent experience on
  behavior, even if one does not realize that one
  is using memory

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Hippocampus and Memory

• The hippocampus may be more important for some
  kinds of memory than others
• Sometimes simple procedural details can yield
  different results

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Brain Damage and Amnesia

• Korsakoffs Syndrome-brain damage caused by
  long-term thiamine deficiency (both retrograde
  and anterograde amnesia)
• Alzheimers Disease-severe memory loss associated
  with aging
• Amyloid beta protein 42-accumulates in the brain
  and impairs neuron function
• Plaques
• Tangles
• Infant Amnesia-possibly due to slow development
  of hippocampus

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Hebbian Synapses

• Hebbs Idea
• A synapse that increases in effectiveness because
  of simultaneous activity in the presynaptic and
  postsynaptic neurons

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A Common Model for Studying Learning

• Aplysia
• Marine Invertebrate/Sea slug
• Fewer and Larger neurons
• Neurons are consistent across all aplysia
• We understand the pathway of the withdrawal
  response-touch results in the withdrawal of the
  siphon, mantle or gill

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Invertebrates and Learning

• Habituation-if you persistently touch the
  aplysias gills, it will stop withdrawing
• Dependent on change in the synapse between the
  sensory and motor neuron
• Sensitization-an increase in response to mild
  stimuli as a result of previous exposure to more
  intense stimuli
• Serotonin blocks potassium channels
  presynaptically resulting in longer action
  potential

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Long-term Potentiation in Mammals

• Defined-a burst of stimulation results in
  potentiated synapses for long periods of time
• Properties of LTP
• Specificity-only the active synapses become
  strengthened
• Cooperativity-nearly simultaneous stimulation by
  two or more axons results in LTP
• Associativity-Pairing a weak input with a strong
  input enhances later response to the weak input

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Biochemical Mechanisms of LTP

• Glutamate receptors involved in LTP
• AMPA-ionotropic receptor opening sodium channels
• NMDA-when partly depolarized, magnesium leaves
  and glutamate opens channel (sodium and calcium
  enter)
• Calcium enhances the later responsiveness of the
  synapse by altering genes and activating proteins

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Figure 13.23  The AMPA and NMDA receptors during
LTP If one or (better) more AMPA receptors have
been repeatedly stimulated, enough sodium enters
to largely depolarize the dendrites membrane.
Doing so displaces the magnesium ions and
therefore enables glutamate to stimulate the NMDA
receptor. Both sodium and calcium enter through
the NMDA receptors channel.
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Calcium Effects on Future Synapses

• AMPA receptor becomes more responsive to
  glutamate
• Some NMDA receptors change to AMPA receptors
• Dendrite builds more AMPA receptors or moves them
  to a better place
• Dendrites make more branches to the axon

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Evidence for an LTP/Learning Link
Mice with abnormal NMDA receptors have difficulty
learning Mice with more than normal NMDA
receptors have super memory Drugs that block
LTP block learning Drugs that facilitate LTP
facilitate learning