Download The Biology of Learning and Memory

Chapter Thirteen
The Biology of Learning and Memory
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
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.
Operant Conditioning
Defined-an individual’s 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
Figure 13.1 Procedures for classical conditioning and operant conditioning
In operant conditioning the learner’s behavior controls the presentation of
reinforcement or punishment.
Lashley’s 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 area’s 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
Figure 13.3 Cuts that Lashley made in the brains of various rats
He found that no cut or combination of cuts interfered
with a rat’s memory of a maze.
Lashley’s 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
Modern Search for the Engram
Simple classical conditioning procedures take place in the lateral
interpositus nucleus
More complex learning paradigms depend on area’s outside of the
cerebellum
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
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
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
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
Hippocampus and Memory
The hippocampus may be more important for some kinds of
memory than others
Sometimes simple procedural details can yield different results
Brain Damage and Amnesia
Korsakoff’s Syndrome-brain damage caused by long-term thiamine
deficiency (both retrograde and anterograde amnesia)
Alzheimer’s 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
Hebbian Synapses
Hebb’s Idea
A synapse that increases in
effectiveness because of
simultaneous activity in
the presynaptic and
postsynaptic neurons
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
Invertebrates and Learning
Habituation-if you persistently touch the aplysia’s 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
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
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
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 dendrite’s membrane. Doing
so displaces the magnesium ions and therefore enables glutamate to
stimulate the NMDA receptor. Both sodium and calcium enter through the
NMDA receptor’s channel.
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
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