Prestimulus cortical activity is correlated with speed of visuomotor processing

Response time (RT) is an important behavioral measure of the overall efficacy of sensorimotor processing and is known to vary significantly from trial to trial. Past work on how stimulus evoked cortical responses contribute to RT variability has helped delineate the stages of neuronal information processing. Much less is known about how the state of the brain immediately preceding the stimulus onset (prestimulus) affects RT. We addressed this problem by analyzing data from three macaque monkeys trained to perform a visuomotor pattern discrimination task. Local field potentials were recorded from up to 16 bipolar surface-to-depth electrodes widely distributed over one cerebral hemisphere in each monkey. The degree of linear correlation between RT and prestimulus spectral power was determined over a wide range of frequencies. In the prefrontal cortex, prestimulus power in the beta range (14-30 Hz) was negatively correlated with RT in two monkeys, suggesting a possible role of activity in this frequency range in the mediation of top-down control of visuomotor processing. In the sensorimotor cortex, prestimulus power in the beta range was positively correlated with RT in two monkeys, consistent with the hypothesis that oscillations in this range support the maintenance of steady-state motor output. In visual occipital and temporal lobe areas, prestimulus power in the alpha/ low beta range (8-20 Hz) showed positive correlations with RT in three monkeys, possibly reflecting a spatially specific disengagement of visual anticipatory attention. Through measurement of prestimulus spectral coherence, it was further determined that sites showing similar patterns of correlation between spectral power and RT were also linked together in synchronized networks.