Cortical and subcortical visual evoked potential correlates of reaction time in monkeys

The relationships between reaction time (RT) and evoked potentials were investigated in three monkeys (Macaca nemestrina) during the performance of a simultaneous brightness discrimination task. Evoked potentials from the lateral geniculate, medial and inferior pulvinar, midbrain reticular formation, hippocampus, and striate and prestriate cortex were recorded concurrently with RT in response to the discriminative stimuli. An early component of the geniculate response and a late positive wave in striate cortex were found to be related systematically to RT. These components were largest for short RTs and diminished progressively in amplitude as RT lengthened. The statistical significance of these relationships was supported by a detailed analysis of single trials. The increases in amplitude of evoked potentials associated with short RTs were attributed to increased arousal level and were discussed in terms of reticular formation modulation of central excitability levels.