Temporal dynamics of attention-modulated neuronal synchronization in macaque V4

It was recently observed that neurons in area V4 exhibited enhanced gamma band (35-90 Hz) synchronization when monkeys attended to a visual stimulus as compared to when they were not attending to the same stimulus (Science 291 (2001) 1560). Spike-triggered averaging of local field potentials (LFPs) was used to show attentional modulation in an early period from 50 to 150 ms after stimulus onset (Science 291 (2001) 1560). In this work we further studied the fine temporal structure in the same data by focusing only on the LFPs without reference to the concurrent spike trains. With the method of adaptive multivariate autoregressive (AMVAR) modeling, we discovered that attentional modulation of gamma power (∼65 Hz) in V4 can be as brief as about 25 ms. Gamma coherence between two V4 recording sites revealed similar attention effects, as well as a second peak around 45 Hz. Directional influences between two V4 populations revealed that one can play a more dominant role than another. These results implicate gamma oscillation as a possible agent in carrying out attention-biased competition among visual stimuli in favor of those that are behaviorally relevant. The AMVAR method was instrumental in revealing the dynamics of gamma frequency synchronization with high temporal and frequency resolution.