Dynamical cell assemblies in the rat auditory cortex in a reaction-time task

Simultaneous single unit spike trains were recorded in the auditory cortex of freely moving rats performing a complex cognitive task. The experimental paradigm is based on a two-choice task (Go/Nogo) with a two-component (pit ch and location) auditory stimulus lasting 500 ms. We report evidence that firstly functional interactions, measured by cross-correlation analysis, be tween single units in the auditory cortex are dynamically modified in the p eriod preceding the onset of the auditory stimulation, referred to as the ' waiting period'. We secondly observed that spatio-temporal firing patterns both within, and across cell spike trains also tended to appear in the wait ing period, several seconds before the actual stimulus delivery. These patt erns indicate a very precise repetition of spike discharges separated by lo ng intervals (up to several hundreds of milliseconds). No consistent change s in mean rate were observed. These results suggest that network activity i n the auditory cortex is selectively modified in rate independent ways befo re the actual sensory stimulation. These modifications may reflect particip ation of recurrent neuronal networks in processes anticipating the expected sensory input. (C) 1998 Elsevier Science Ireland Ltd. All rights reserved.