Synchronous membrane potential fluctuations in neurons of the cat visual cortex.

We have recorded intracellularly from pairs of neurons less than 500 microm distant from one another in V1 of anesthetized cats. Cross-correlation of spontaneous fluctuations in membrane potential revealed significant correlations between the cells in each pair. This synchronization was not dependent on the occurrence of action potentials, indicating that it was not caused by mutual interconnections. The cells were synchronized continuously rather than for brief epochs. Much weaker correlations were found between the EEG and intracellular potentials, suggesting local, rather than global, synchrony. The highest correlation occurred among cells with similar connectivity from the LGN and similar receptive fields. During visual stimulation, correlations increased when both cells responded to the stimulus and decreased when neither cell responded.