RESEARCH ARTICLE Motor selection dynamics in FEF explain the reaction time variance of saccades to single targets Christopher K Hauser, Dantong Zhu, Terrence R Stanford, Emilio Salinas* Department of Neurobiology and Anatomy, Wake Forest School of Medicine, Winston-Salem, United States Abstract In studies of voluntary movement, a most elemental quantity is the reaction time (RT) between the onset of a visual stimulus and a saccade toward it. However, this RT demonstrates extremely high variability which, in spite of extensive research, remains unexplained. It is well established that, when a visual target appears, oculomotor activity gradually builds up until a critical level is reached, at which point a saccade is triggered. Here, based on computational work and single-neuron recordings from monkey frontal eye field (FEF), we show that this rise-to- threshold process starts from a dynamic initial state that already contains other incipient, internally driven motor plans, which compete with the target-driven activity to varying degrees. The ensuing conflict resolution process, which manifests in subtle covariations between baseline activity, build- up rate, and threshold, consists of fundamentally deterministic interactions, and explains the observed RT distributions while invoking only a small amount of intrinsic randomness. DOI: https://doi.org/10.7554/eLife.33456.001 Introduction The reaction time (RT) represents the total time taken to perform all of the mental operations that may contribute to a particular action, such as stimulus detection, attention, working memory, or motor preparation. Although the importance of the RT as a fundamental metric for inferring the *For correspondence: mechanisms that mediate cognition cannot be overstated (Welford, 1980; Meyer et al., 1988),
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