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SUMMARY:A Study of Certain Models of Synaptic Plasticity in the Cerebellum
  and Neocortex - David Higgins (Ecole Normale Superieure\, Paris)
DTSTART:20140916T090000Z
DTEND:20140916T100000Z
UID:TALK54306@talks.cam.ac.uk
CONTACT:Henning Sprekeler
DESCRIPTION:Synaptic plasticity is the ability to change the influence tha
 t spiking in a presynaptic neuron has on a postsynaptic cell. Intracellula
 r calcium elevation and relative spike timing are processes typically asso
 ciated with synaptic plasticity outcomes throughout the brain. Plasticity 
 of the parallel fibre to Purkinje cell synapse in the Cerebellum is seen a
 s being atypical in that it is non-Hebbian\, depending on an ‘error sign
 al’ via the activation of the climbing fibre for LTD and on presynaptic 
 NMDA receptors for LTP. Here I develop a spike based model of plasticity f
 or this synapse\, based on calcium and NO\, which accurately fits a  range
  of protocols from the literature and has been shown to have wide predicti
 ve power. I then move on to developing an analysis of a more typical\, cal
 cium-based\, plasticity model for neocortical synaptic plasticity [Graupne
 r12]. I develop analytical tools which accurately predict the behaviour of
  this synapse model under Poisson pre- and postsynaptic firing. Finally\, 
 I extend this theory to predict the behaviour of a large-scale recurrent n
 etwork of leaky integrate-and-fire neurons under both constant and time-va
 rying noisy external inputs. Investigation of both plasticity models revea
 ls insights into the processes of learning and subsequent forgetting in th
 e brain. Both models reveal the joint importance of burst frequency and re
 lative spike timing in the induction of memory changes at the synaptic lev
 el. Adjustment of model parameters to more closely mimic in-vivo condition
 s extends the retention time of memories\, under ongoing activity\, to bio
 logically relevant time scales. This work represents a coherent developmen
 t right through from the biophysical processes of synaptic plasticity to t
 he analytical mean-field level.
LOCATION:Cambridge University Engineering Department\, CBL\, BE-438 (http:
 //learning.eng.cam.ac.uk/Public/Directions)
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