Behavioral/Systems/Cognitive Deliberation in the Motor System: Reflex Gains Track Evolving Evidence Leading to a Decision

Both decisionmaking and sensorimotor control require real-time processing of noisy information streams. Historically these processes were thought to operate sequentially: cognitive processing leads to a decision, and the outcome is passed to the motor system to be converted intoaction.Recently, it hasbeensuggested that thedecisionprocessmayprovidea continuous flowof information to themotor system, allowing it to prepare in a graded fashion for the probable outcome. Such continuous flow is supported by electrophysiology in nonhuman primates. Here we provide direct evidence for the continuous flow of an evolving decision variable to the motor system in humans. Subjects viewed a dynamic randomdot display andwere asked to indicate their decision about direction bymoving a handle to one of two targets. We probed the state of the motor system by perturbing the arm at random times during decision formation. Reflex gains were modulated by the strength and duration of motion, reflecting the accumulated evidence in support of the evolving decision. The magnitude and variance of these gains tracked a decision variable that explained the subject’s decision accuracy. The findings support a continuous process linking the evolving computations associated with decision making and sensorimotor control