JPSTH paper

[hiro]

The following paper has been accepted for publication in Neural Computation and 
is available from

http://www.kyoto-su.ac.jp/~hiro/jpsth_rev3.pdf

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Model Dependence in Quantification of Spike Interdependence by Joint 
Peri-Stimulus Time Histogram

Hiroyuki Ito and Satoshi Tsuji

Department of Information and Communication Sciences, Faculty of 
Engineering, Kyoto Sangyo University, Kita-ku, Kyoto 603-8555, 
Japan and CREST, Japan Science and Technology.

ABSTRACT
Multineuronal recordings have enabled us to examine context-
dependent changes in the relationship between the activities of 
multiple cells. The Joint Peri-Stimulus Time Histogram (JPSTH) is a 
much-used method for investigating the dynamics of the 
interdependence of spike events between pairs of cells. Its results are 
often taken as an estimate of interaction strength between cells, 
independent of modulations in the cells' firing rates. We evaluate the 
adequacy of this estimate by examining the mathematical structure of 
how the JPSTH quantifies an interaction strength after excluding the 
contribution of firing rates. We introduce a simple probabilistic model 
of interacting point processes to generate simulated spike data, and 
show that the normalized JPSTH incorrectly infers the temporal 
structure of variations in the interaction parameter strength. This 
occurs because, in our model, the correct normalization of firing rate 
contributions is different to that used in Aertsen et al.'s ``effective 
connectivity" model. This demonstrates that firing rate modulations 
cannot be corrected for in a model-independent manner; and therefore 
the effective connectivity does not represent a universal characteristic 
that is independent of modulation of the firing rates. Aertsen et al.'s 
effective connectivity may still be used in the analysis of experimental 
data, provided we are aware that this is simply one of many ways of 
describing the structure of interdependence. We also discuss some 
measure-independent characteristics of the structure of 
interdependence.

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Regards.

Hiroyuki Ito
Dept. of Information & Communication Sci.
Faculty of Engineerings
Kyoto Sangyo University
JAPAN
e-mail: hiro at ics.kyoto-su.ac.jp