Chapter ThirteenThe 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 ratsHe 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 agingAmyloid beta protein 42-accumulates in the brain and impairs
neuron functionPlaquesTangles
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 withdrawingDependent on change in the synapse between the sensory
and motor neuronSensitization-an increase in response to mild stimuli as a result of
previous exposure to more intense stimuliSerotonin 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 LTPAMPA-ionotropic receptor opening sodium channelsNMDA-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 LTPIf 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 glutamateSome NMDA receptors change to AMPA receptorsDendrite builds more AMPA receptors or moves them to a better
placeDendrites 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