FUNCTIONAL CONNECTIVITY WITHIN THE VISUAL-CORTEX OF THE RAT SHOWS STATE CHANGES

The aim of this study was to investigate the dynamics of the horizonta l functional connectivity within the visual cortex during spontaneous activity or during visual stimulation. Two arrays of 16 electrodes wer e inserted in the visual cortex of a rat. From these electrodes a dept h profile was Obtained of the local spiking activity. The crosscorrela tions between all electrodes were estimated. Three types of cross-corr elation peaks were identified and classified as; 'thin peaks', 'fast w aves' and 'slow waves'. Partialization was applied, a mathematical met hod to reduce the amount of common input in correlations, and its effe ct on the three types of correlation peaks was studied. Slow waves wer e found to be the most vulnerable to partialization and thin peaks the least. From these observations it was concluded that the three types of peaks represent synchronous neuronal assemblies of different magnit ude; slow waves large, fast waves intermediate and thin peaks assembli es composed of small numbers of neurons. Large changes were observed i n the types of cross-correlations and their spatial distribution withi n the set of interarray combinations of electrodes. These changes were spontaneous, and could not be related to the visual simulation. Two s tates were identified; the 'thin-peak' state and the 'slow-wave' state . The 'thin-peak' state is interpreted as occurring at a light level o f anaesthesia and is characterized by the presence of thin peaks in al l combinations of electrodes. Thin peaks with the largest strength wer e found in the upper interarray electrode combinations. The 'slow-wave ' state is interpreted as occurring at a deep level of anaesthesia and is characterized by the presence of exclusively slow waves, which wer e limited mostly to the middle and lower interarray combinations of el ectrodes. Activation of the cortex is thus associated with the appeara nce of synchrony between small groups of neurons (thin peaks) which, i n contrast to the slow-wave slate, include the upper layers of the cor tex.