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Eugene Izhikevich
Brain Corporation, USA
Thursday 26 November 2009
15.00
Seminar Room B10 (Basement)
Alexandra House, 17 Queen Square, London, WC1N 3AR
Spike-Timing Theory of Working Memory
Working memory is part of the brain's memory system that provides temporary storage and manipulation of information necessary for cognition. Although working memory has limited capacity at any given time, it has vast memory content in the sense that it acts on the brain's nearly infinite repertoire of lifetime memories. We show that large memory content and WM functionality emerge spontaneously if we take the spike-timing nature of neuronal processing into account. Here, memories are represented by extensively overlapping groups of neurons that exhibit stereotypical time-locked spatiotemporal spike-timing patterns, called polychronous patterns. Using simulations, we show how associative synaptic plasticity in the form of short-term STDP selects such polychronous neuronal groups (PNGs) into WM by temporarily strengthening the synapses of the selected PNG. This strengthening increases the spontaneous reactivation frequency of the selected PNGs, resulting in irregular, yet systematically changing elevated firing activity patterns consistent with those recorded during WM tasks. Our theory explains the relationship between such slowly changing firing rates and precisely timed spikes, and it also reveals a novel relationship between WM and the perception of time on the order of seconds.