EVIDENCE FOR SYNCHRONIZED RESPONSES IN THE PIRIFORM CORTEX BY USING GIBBS POTENTIAL ANALYSIS

The piriform cortex is a large paleocortical area which receives direc t projections from the olfactory bulb. In order to study the spatiotem poral distribution of the piriform cortex activity, we chose optical r ecording of the responses evoked by olfactory bulb electrical stimulat ion. Such a stimulation elicited a large signal corresponding to corti cal reactivation (disynaptic activity) via intrinsic association fibre s. As the disynaptic activity was observed over the entire piriform ar ea, we wondered whether or not this redistribution contributes to a sy nchronisation of the activity in the piriform cortex. In order to answ er this question, we developed a statistical approach which allows us to take the temporal dimension into account. The analysis was performe d by using the Gibbs potential analysis. The neural response of the di ode is represented by a stochastic point process (occurrence of latenc y peak), and the response of the diode array is given as successive re alisations of a binary random field defined on a finite set. The Gibbs measure associated with this field is then estimated through the inte raction potentials of the field's configurations, which provide a quan titative evaluation of the interaction and the synchronisation between the neural sites. The analysis was performed on the latency of the pe ak of disynaptic activity, which was determined from signals from 60 d ifferent acquisitions realised with the same stimulus parameters. From these 60 files of latency values, we estimated the Gibbs interaction potential of singletons and pairs. The former gave an image of the spa tiotemporal distribution of the disynaptic activity, which appears to propagate from the anterior to the posterior part of the area recorded . The estimation of the interaction potential of pairs allows us to ch aracterise the degree of synchronisation between two neighbouring reco rding sites. It appeared that, in the anterior half of the area record ed, the disynaptic activity was statistically desynchronised whereas, in the posterior part the disynaptic activity appeared strongly synchr onised. The functional implications of such a spatiotemporal distribut ion of the activity are discussed.