The time course of attention-modulated gamma frequency synchronization in macaque V4.

H. Liang, S.L. Bressler, M. Ding, R. Desimone, P. Fries.

CCSBS FAU, Boca Raton FL; LN NIMH NIH, Bethesda MD

It has recently been shown that gamma band (35-90 Hz) synchronization is enhanced among V4 neurons activated by an attended stimulus as compared to neurons activated by distracters (Fries et al, Science, 2001). Here, we investigated the detailed time course of this attentional modulation by Adaptive MultiVariate AutoRegressive (AMVAR) modeling (Ding et al, Biol Cyber, 2000). For multiple simultaneously recorded local field potentials from V4, we obtained power and coherence spectra in 50 ms windows shifted over the data in millisecond steps. As the monkey fixated centrally, two patches of moving high contrast square wave grating were presented at equal eccentricity, one inside and one one outside the receptive field (RF) of the recorded neurons. On alternate trials, the monkey was cued to attend to either one of them. At ~115 ms poststimulus, there was a brief increase in gamma power, peaking ~65 Hz. The gamma power peak was accompanied by a peak in coherence among a subset of recording sites. At ~160 ms poststimulus, a second coherence peak occurred at ~45 Hz, but with no corresponding power peak. Attention to the stimulus inside the recorded neurons' RF enhanced the observed gamma power and coherence. These results support the idea that attention biases competition among visual stimuli in favor of those that are behaviorally relevant (Desimone & Duncan, Ann Rev Neurosci, 1995), and suggest that increased gamma frequency synchronization to attended stimuli may enhance the impact of activated V4 neurons on their targets. The AMVAR method was instrumental in revealing the dynamics of gamma frequency synchronization with high temporal and frequency resolution.

NIMH, NSF, NIMH-IRP