The Journal of Neuroscience, March 15, 2003, 23(6):2394
Decoding Spike Trains Instant by Instant Using Order Statistics
and the Mixture-of-Poissons Model
Matthew C.
Wiener and
Barry J.
Richmond
Laboratory of Neuropsychology, National Institute of Mental Health,
National Institutes of Health, Department of Health and Human Services,
Bethesda, Maryland 20892-4415
In the brain, spike trains are generated in time and presumably
also interpreted as they unfold in time. Recent work (Oram et al.,
1999; Baker and Lemon, 2000) suggests that in several areas of the
monkey brain, individual spike times carry information because they
reflect an underlying rate variation. Constructing a model based on
this stochastic structure allows us to apply order statistics to decode
spike trains instant by instant as spikes arrive or do not. Order
statistics are time-consuming to compute in the general case. We
demonstrate that data from neurons in primary visual cortex are
well fit by a mixture of Poisson processes; in this special case, our
computations are substantially faster. In these data, spike timing
contributed information beyond that available from the spike count
throughout the trial. At the end of the trial, a decoder based on the
mixture-of-Poissons model correctly decoded about three times as many
trials as expected by chance, compared with approximately twice as many
as expected by chance using the spike count only. If our model
perfectly described the spike trains, and enough data were available to
estimate model parameters, then our Bayesian decoder would be optimal.
For four-fifths of the sets of stimulus-elicited responses, the
observed spike trains were consistent with the mixture-of-Poissons
model. Most of the error in estimating stimulus probabilities is
attributable to not having enough data to specify the parameters of the
model rather than to misspecification of the model itself.
Key words:
visual cortex; information; coding; modeling; statistics; timing
Copyright © 2003 Society for Neuroscience 0270-6474/03/2362394-13$05.00/0