Manuscript in Preparation:
How Neurons May Respond to Temporal Structure in their Inputs
Bartlett W. Mel
Department of Biomedical Engineering
USC
Ernst Niebur
Zanvyl Krieger Mind/Brain Institute and Dept. of Neuroscience
Johns Hopkins University
David W. Croft
Tanner Research Corporation
ABSTRACT
It has been suggested that the visual system and other sensory
systems use temporal codes. We study how neurons respond to
temporal structure in their inputs using simulations of (1) a
164-compartment pyramidal cell with passive or active
dendrites, and NMDA or non-NMDA type synaptic input, and (2) a
single-compartment integrate-and-fire neuron with either
shallow or deep post-spike reset. In each run, 100 randomly
placed excitatory synapses were activated at 100 Hz and the
cell's mean output firing rate was recorded over 500 ms. In
different runs, and over a range of peak excitatory synaptic
conductances, the temporal structures of input spike trains was
varied along 2 continuous dimensions: synchronicity (S) and
periodicity (P). S=0 meant complete asynchrony and S=1 complete
synchrony among trains; P=0 meant Poisson and P=1 periodic
trains. Contrary to expectations, we observed that
synchronizing synaptic inputs had only modest and inconsistent
effects on output firing rates, whereas firing rates increased
more consistently and substantially with increases in P, i.e.
as spike trains became individually more regular, whether or
not synchronized. We identify the biophysical mechanisms that
account for these results, and test their applicability under a
wide variety of biophysical conditions.
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