Sensory responses of the brain are known to be highly variable, but the origin and functional relevance of this variability/nhave long remained enigmatic. Using the variable foreperiod of a visual discrimination task to assess variability in the/nprimate cerebral cortex, we report that visual evoked response variability is not only tied to variability in ongoing cortical/nactivity, but also predicts mean response time. We used cortical local field potentials, simultaneously recorded from/nwidespread cortical areas, to gauge both ongoing and visually evoked activity. Trial-to-trial variability of sensory evoked/nresponses was strongly modulated by foreperiod duration and correlated both with the cortical variability before stimulus/nonset as well as with response times. In a separate set of experiments we probed the relation between small saccadic eye/nmovements, foreperiod duration and manual response times. The rate of eye movements was modulated by foreperiod/nduration and eye position variability was positively correlated with response times. Our results indicate that when the time/nof a sensory stimulus is predictable, reduction in cortical variability before the stimulus can improve normal behavioral/nfunction that depends on the stimulus.

The research leading to these results has received funding from the European Union Seventh Framework Programme (FP7/2007–2013) under grant agreement no. 269921 (BrainScaleS). AL is supported by the Ramon y Cajal program from the Spanish government. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.