MULTIUNIT NORMALIZED CROSS-CORRELATION DIFFERS FROM THE AVERAGE SINGLE-UNIT NORMALIZED CORRELATION

As the technology for simultaneously recording from many brain locatio ns becomes more available, more and more laboratories are measuring th e cross-correlation between single-neuron spike trains, and between co mposite spike trains derived from several undiscriminated cells record ed on a single electrode (multiunit clusters). The relationship betwee n single-unit correlations and multiunit cluster correlations has not yet been fully explored. We calculated the normalized cross-correlatio n (NCC) between single-unit spike trains and between small clusters of units recorded in the rat somatosensory cortex. The NCC between small clusters of units was larger than the NCC between single units. To un derstand this result, we investigated the scaling of the NCC with the number of units in a cluster. Multiunit cross-correlation can be a mor e sensitive detector of neuronal relationship than single-unit cross-c orrelation. However, changes in multiunit cross-correlation are diffic ult to interpret uniquely because they depend on the number of cells r ecorded on each electrode and because they can arise from changes in t he correlation between cells recorded on a single electrode or from ch anges in the correlation between cells recorded on two electrodes.