Mode changes in activity of single neurons in anterior insular cortex across trials during multi-trial reward schedules

Abstract

We previously showed that spike count response distributions in anterior cingulate neurons can be fitted by a mixture of a few Poisson distributions in our reward schedule task. Here we report that the neuronal responses in insular cortex, an area connected to anterior cingulate cortex, can also be nicely fitted. The ratio of Poisson distributions changed with schedule progress, suggesting that neuronal responses in these areas fall into discrete firing modes. More insular neurons show mode changes across the schedules. The selection of firing modes might be related to cognitive processes, but seems independent across the two areas.Keywords single unit; spike count; Poisson distribution; neural coding; response variability; rhesus monkey; reward expectancyThe numbers of spikes emitted by single neurons are often different even when the trial type is repeated several times. Describing responses according to their means and variances can be adequate when the distributions are unimodal. Wiener and Richmond (2002) pointed out that the distributions of spike counts across repeated trials in V1 could be fitted nicely using a mixture of a small number (usually 3 or fewer) of Poisson distributions. Each distribution has a different mean rate. Because the types and amounts of serial correlations within the spike trains will depend on the specific mixture of Poisson processes, responses represented by different mixtures of Poisson processes will have different temporal correlation structures. When monkeys performed a reward schedule task the spike counts of the neuronal responses in anterior cingulate cortex were well fitted by a mixture of small number of Poisson distributions (Shidara et al. 2005). Furthermore, the ratio of the mixtures of Poisson components seemed correlated with schedule progress in the reward schedule task. This mixture of Poisson distributions seemed to account for much of the non-Poisson temporal structure of the spike trains. We speculated that the cognitive states that were exhibited during Correspondence should be addressed to Munetaka Shidara, Graduate School of Comprehensive Human Sciences, University of Tsukuba, 1-1-1 Amakubo, Tsukuba, Ibaraki 305-8577, Japan. E-mail: mshidara@md.tsukuba.ac.jp, Phone & FAX: +1-81-29-853-5903 Publisher's Disclaimer: This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final citable form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain. performance of the reward schedule task might underlie probability changes in higher and lower firing components in anterior cingulate neurons. Richmond et al. (2003) conceptualized anterior cingulate as a part of system related to the balance between work and reward. Their no...

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