Stimulus-specific fast oscillations at zero phase between visual areas V1 and V2 of awake monkey.

Synchronization of fast cortical oscillations (35-90 Hz) has been proposed as a basis of sensory integration. This hypothesis requires stimulus specific oscillations that occur synchronously in different cortical areas of awake animals. Here, we demonstrate the presence of, and phase-locking between, high amplitude stimulus specific oscillations (50-90 Hz) in striate (V1) and extra striate (V2) visual cortex of an awake monkey. Oscillations of multiple unit spikes and local field potentials occurred with an average V1-V2 phase difference near zero. This finding was unexpected because V1 and V2 are thought to be serially arranged in the primate's visual processing stream. However, near zero-phase synchronization among cortical areas might enable fast and effective communication via the many reciprocal cortico-cortical connections for processes such as sensory integration.