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