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