Dynamics of striate cortical activity in the alert macaque: II. Fast time scale synchronization

Synchronous neuronal activity with millisecond precision has been postulate d to contribute to the process of visual perceptual grouping. We have perfo rmed multineuron recordings in striate cortex of two alert macaque monkeys to determine if the occurrence and properties of this form of activity are consistent with the minimal requirements of this theory. We find that neuro nal synchronization with millisecond precision is a prevalent and robust fe ature of stimulus-evoked activity in striate cortex. It occurs among adjace nt cells recorded by the same electrode (<120 <mu>m), among cells recorded at separate but nearby sites (300-400 mum) and between cells recorded at lo cations separated by 3-4 mm. The magnitude and probability of synchronous f iring is inversely related to the spatial separation between the cells and it occurs within and between groups of cells that are both tuned and untune d for stimulus orientation and direction. Among those tuned for orientation , cell pairs separated by <400 <mu>m showed no clear dependence of correlat ed firing on orientation preference. The occurrence of gamma-band (20-70 Hz ) oscillations in the cellular firing patterns was a strong predictor of sy nchronous firing at each of the spatial scales. Nearly 90% of the cell pair s showing significant correlation also showed oscillatory firing in one or both cells of the pair. These results are consistent with some, but not all , of the previous reports of synchronous activity in striate cortex of both cat and primates. The similarities in the properties of synchronous oscill ations in the monkey and cat suggest that this form of neuronal activity is a general property of mammalian striate cortex. The relation between corre lation and oscillation suggests that neuronal rhythmicity is an important m echanism contributing to synchronization.