Synchronous activity in the visual system

Synchronous activity among ensembles of neurons is a robust phenomenon observed in many regions of the brain. With the increased use of multielectrode recording techniques, synchronous firing of ensembles of neurons has been found at all levels in the mammalian visual pathway, from the retina to the extrastriate cortex. Here we distinguish three categories of synchrony in the visual system, (a) synchrony from anatomical divergence, (b) stimulus-dependent synchrony, and (c) emergent synchrony (oscillations). Although all three categories have been well documented, their functional significance remains uncertain. We discuss several lines of evidence both for and against a role for synchrony in visual processing: the perceptual consequences of synchronous activity, its ability to carry information, and the transmission of synchronous neural events to subsequent stages of processing.