Electrophysiological correlates to the intrinsic optical signal in the rat neocortical slice.

The study sought to further our understanding of the correlation between electrophysiological activity and the intrinsic optical signal (IOS) in neocortical slice by combining imaging of IOS with whole-cell and extracellular electrical recording. Columnar-shaped areas of IOS were evoked with electrical stimulation of the layer VI/white matter border. The distribution of IOS intensities linearly correlated with the distribution of evoked excitatory post-synaptic potential amplitudes (R=0.89). The distribution of field potentials was narrower than the distribution of IOS intensities with significantly smaller amplitude of the normalized field potentials in the edge of the column. The data suggest that in the neocortical slice the IOS at the edge of the evoked column reflects primarily the sub-threshold excitatory synaptic activity.