Lecture 13/14

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University of Toronto St. George
Cell and Systems Biology
Melanie Woodin

CSB332H1S L13/14; Feb. 27, 2012  Bi & Poo 1998 Synaptic Plasticity & Learning and Memory  STDP w (-)ve spike-timing intervals induces LT Synaptic Modifications in Cultured Hippocampal Neurons: Dependence on  Post then Pre, same timing, Spike Timing, Synaptic Strength, and Postsynaptic Cell Type about 10ms interval  The Journal of Neuroscience, December 15, 1998, 18(24):10464-  Get decrease in amplitude 10472 (LTD)  Guo-qiang Bi and Mu-ming Poo Spike-Timing Dependent Synaptic Plasticity (STDP)  %age change in EPSC  Instead of inducing LTP w high-freq presynaptic stimulation, spike- amplitude at 20-30 min timing protocols use lower-freqs w paired pre- & postsynaptic activity after repetitive  (+)ve spike-timing interval: EPSP arrives before postsynaptic AP is coincident spiking (60 fired pulses at 1 Hz) plotted  (-)ve spike-timing interval: EPSP arrives after postsynaptic AP is fired against spike timing.  Pair pre & postsynaptic act pots during induction  Spike timing defined by time interval (t) btwn  Decide ahead of time what protocol to use, can choose from 2 onset of EPSP & peak of intervals: postsynaptic act pot during each cycle of  Positive spike-timing intervals induce LTP o Pair Pre & Post activity repetitive stimulation, as o (pair EPSPs w postsynaptic Act Pot) illustrated by the traces o Regulate timing interval, uses dif ones above.  Negative spike timing intervals induce LTD Summary figure:  Critical window for induction of o Reverse order of pairing, Post then Pre o Can get another act pot during repolarization phase synaptic potentiation & depression.  LTP & LTD can also be  Spiking-timing windows – importance of timing in dif brain structures induced by low freq (1-10Hz)  Each expt like before is summarized as one data pt  Ex. -10ms: Post then Pre  20% decrease in amplitude coincident pre- & postsynaptic activity  Asymmetry – sits right at 0 pt of spike-timing interval  B: want to assess strength of o So if induce btwn 0 & 20ms  on avg increase synapse strength; synapse on own, at low freq, but if reverse pairing  depression record for about 15min, o So can get LTP & LTD w same freq of act pots but what matters is dotted line = avg current if Pre is before Post amplitude (30pico amps) o So Hebb is right, when Cell A fires (+)ve EPSP repeatedly at Cell B o (+)ve spike timing (to summate)  LTP interval, 5-10-15ms interval  Can use for glutaminergic & gaba-ergic synapses w computations to o On avg, all pts now predict brain reaction above baseline, so o Can also use for artificial intelligence & prosthetics; ex. cochlear induced LTP implants  C: avg of many expts, overall  LTP induction: similar mech as titanic induction, difference is how we have increase in current get the membrane depolarization amplitude o Now the postsynaptic act pot removes the Mg block o Have no change w  LTD induction: Ca influx much lower, dif signal cascade that control dephosphorylates AMPARs The Woman Who Could Not Forget (not required)  http://www.youtube.com/watch?v=SoxsMMV538U&feature=related o As constantly recalling event (whether consciously or not or during dreams, or subconsciously), constantly modify the memory  Can associate w newer events  Can be divided into: o Episodic memory  Knowledge about the event of learning something o Semantic memory  Knowledge independent of context  Requires hippocampus & certain regions of cerebral cortex  Hippocampus lays down / forms memories but does not store them  Mostly talking about episodic (declarative) memory – facts & events  During consolidation, leaves hippocampus  cortex o Hippocampus (in medial temporal lobe) o Memories stored at dif synapses in dif neurons in brain  Nondeclarative – Procedural (not lost when lose hippocampus, also o Associate in regions in brain of the sensory system that brought can tell directions to get to bathroom) that memory in – so like reactivating the sensory input  Consolidation 2-4wks after acquiring memory o Sleep = important, but not known what is so essential about it Procedural Memory  aka implicit memory o If record from hippocampus during sleep: same neurons firing in  the long-term memory of skills & procedures
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