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Unformatted text preview: Memory Neural Level How does Learning Occur at Neural Level? Donald Hebb (1904 1985) Neurons that fire together, wire together (1949). Hebbian learning Unsupervised Increase in synaptic strength when two neurons both active. First Experimental Evidence Bliss & Lomo (1973) LongTerm Potentiation (LTP) Initially shown in rabbit hippocampus Rapidly repeating injection of current into axon causes increased postsynaptic response (increased EPSP in dendrites of postsynaptic cell). LTP Evidence (PostTetanic Potentiation) Rectangles: response in dendrite to test stimulus a current pulse into axon lasting 100 us. Tetanus: sequence of 100 test stimuli, 10 ms apart. LTP Specificity ++ : strong tetanus : no tetanus dendrites LTP No LTP ++ axons LTP Cooperativity ~~ : weak tetanus : no tetanus NO LTP ~~ NO LTP LTP ~~ LTP No LTP ~~ LTP Nitty Gritty At synapse, glutamate (neurotransmitter) binds to AMPA + receptors, allowing Na to enter dendrite, causing EPSP Activated synapses are "tagged" (with specific protein) If cell body becomes sufficiently depolarized (spatial and temporal summation of EPSPs), NMDA receptors open, 2+ allowing Ca to enter the cell. 2+ Ca activates pathway that leads to gene transcription that produces proteins for AMPA receptors AMPA receptors are added at "tagged" synapses only LTP Gene transcription AMPA receptors Enzymes EPSPs glutamate AMPA() + Na NMDA() AMPA() tag + Na 2+ Ca glutamate tag BehaviorLTP Link? Mice genetically modified to have increased numbers of NMDA receptors These mice learned spatial tasks faster than control mice Called "Doogie mice", after Doogie Howser ...
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This note was uploaded on 07/29/2008 for the course NEUROSCIEN 70 taught by Professor Whitney during the Spring '08 term at Johns Hopkins.
- Spring '08