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Chapter 12

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Janelle Leboutillier

12 | LEARNING AND MEMORY Learning - behaviour of organisms separated into three major categories 1) reflexes: involuntary response to a stimulu 2) instinct: stereotyped pattern of behaviour elicited by particular environmental stimuli 3) learning: relatively permanent change in behaviour or capacity for behaviour due to exp. Types of Learning - associative learning: type of learning that involves formation of a connection between two elements or events - nonassociative learning: type of learning that involves change in magnitude of responses to stimuli rather than formation of connections between elements or events Habituation and Sensitization - habituation: type of learning in which response to repeated, harmless stimulus becomes progressively weaker - sensitization: type of learning in which experience of one stimulus heightens response to subsequent stimuli Classical Conditioning - classical conditioning: type of associative learning in which neural stimulus acquires ability to signal occurrence of a second, biologically significant event - conditioned stimulus (CS): initially neutral event that takes on ability to signal other biologically significant events - unconditioned stimulus (UCS): event that elicits a response w/out prior exp. - conditioned response (CR): learned reaction to conditioned stimulus - unconditioned response (UCR): event that elicits a response w/out prior experience Using Invertebrates to Study Learning - research relied on sea slug, aplysia californica: invertebrate sea slug frequently used as subject of experiments on learning and memory - it’s anatomy  dorsal surface=gillcovered by structure known as mantle shelf  one end of mantle shelf=siphon (tube which animal releases waste and seawater); touching it produces gill-withdrawal reflex: protective reflex in which gill is retracted in response to touch Habituation in Aplysia - figure 12.3, p.343  have neural nets=serve as major processing centres  siphonserved by 24 touch receptors located in animal’s abdominal ganglion  touch receptors in abdominal ganglionform synapses w/ # of excitatory and inhibitory interneurons & six motor neurons serving gill - explanation: repeated touching of siphon=changes at synapses between sensory neurons of siphon and motor neurons that serve gill muscles  repeated touching=reduced size of excitatory postsynaptic potentials – figure 12.4, p.344  reduced activity at synapse=direct result of release of less neurotransmitter - can last up to three weeks  probably depends on postsynaptic processes involving NMDA glutamate receptor (participate in structural changes accompanying learning; blocking these receptors=prevent development of long- term habituation) Sensitization in Aplysia - figure 12.4, p.344 - compared to habituation (single pathway), in sensitization- stimulus gains ability to influence more than one neural pathway - shocking animal’s tail  stimulates sensory neurons (forms excitatory synapses w/ group of interneurons)  interneurons form synapses w/ sensory neurons serving siphon (synapses are axo-axonic in form)  interneurons release serotoninsensory axon terminal bind these molecules=metabotropic process=close potassium channels=action potentials reach sensory axon terminal=last longer  longer action potentials=great influx of calcium into sensory neuron=release larger amounts of neurotransmitter by sensory axon terminal=stronger response by motor neurons and gill muscles=stronger gill-withdrawal reflex - adjustments at synaptic lvl=immediate changes seen in habituation and sensitization - longer-lasting changes=structural modifications to neurons – figure 12.5, p.346  dendrites of motor neurons modified to accommodate increased # of presynaptic elements  involve actin (protein makes up microfilaments of cytoskeleton) - postsynaptic changes  increase in #s of AMP receptor (type of glutamate receptor)  coordination of pre- and postsynaptic changes=retrograde signals (postsynaptic motor cell back to presynaptic sensory cell or interneuron) Classical Conditioning in Aplysia - figure 12.6, p.347 Memory Types of Memory - information processing models: theories of memory that seek to explain management of info by brain, from detection to storage to retrieval – figure 12.11, p.353 (Atkinson-Shiffrin model)  initially enters sensory memory: initial stage in memory formation in which large amounts of data can be held for very short periods  short-term memory (working memory): intermediate memory store in which limited amounts of data can be held for a limited amount of time; w/out further processing=info is permanently lost  limited capacity (5-9 unrelated items)  when try to add more items=previous info often lost  temporary nature  sorted into temporary storage areas for auditory, visual, or combined types of info (managed by central executive process)  long-term memory: memory store in which apparently unlimited amounts of data can be held for unlimited amount of time – figure 12.12, p.354  divided into three categories 1) semantic memory: type of declarative, explicit memory for facts and verbal info 2) episodic memory: type of declarative, explicit memory for personal exp. 3) procedural memory: type of implicit memory for performing learned skills and tasks  declarative memories: explicit memory for semantic and episodic info that can easily be verbalized, or “declared”  declarative vs. proceduralusually recalled unconsciously or implicitly - distinction between explicit and implicit memories demonstrated in anterograde amnesia: memory loss for info processed following damage to brain  don’t recall solving Tower of Hanoi puzzle, but are able to solve it regardless (brain damage didn’t prevent from forming implicit memories of puzzle)  how? extended search for engram: physical memory trace in the brain Brain Mechanisms in Memory Early Efforts to Locate Memory Functions - Lashley reasoned engram might be located in association cortex  Figure 12.13, p.355 –what mattered was the size of the lesion that affected the rats’ performance (regardless of where lesion was made)  Mistakenly concluded: all parts of cortex=equipotentiality and mass action - why Lashley wrong? 1) parts of cortex not equally likely to participate in memory 2) maze learning is comple task involving # of sensory and motor processes - temporal lobe & single-cell recording The Temporal Lobe and Memory - significant evidence from case studies of patients w/ anterograde amnesia –most thoroughly studied= H.M. – figure 12.14, p.356hippocampus, amygdala, and association cortex of temporal lobe removed from both hemispheres  anterograde amnesia was profound- couldn’t transfer new info from short-term to long-term  surgery didn’t affect all types of memory equally  could perform mirror-drawing task: figure 12.15, p.357 - case of H.M. provides support for differentiation of explicit and implicit memories and stage approach in atkinson-shiffrin model  damage to medial temporal lobe=affects explicit memories  didn’t affect long-term memories already stored  hippocampus unlikely storage location for elusive engram  retain fairly stable memories presurgical lives=don’t reside in medial temporal lobe itself - figure 12.16, p.358 –solving problem after delay requires use of long-term memories  delayed nonmatching to sample (DNMS) task: standard test of memory in which subject must identify novel member of a stimulus pair following a delay  monkeys w/ medial temporal lobe lesions in both hemispheres=performed poorly - structures damaged by medial temporal lobe lesions  amygdala (emot
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