Abstract
BackgroundHuman movement can be guided automatically (implicit control) or attentively (explicit control). Explicit control may be engaged when learning a new movement, while implicit control enables simultaneous execution of multiple actions. Explicit and implicit control can often be assigned arbitrarily: we can simultaneously drive a car and tune the radio, seamlessly allocating implicit or explicit control to either action. This flexibility suggests that sensorimotor signals, including those that encode spatially overlapping perception and behavior, can be accurately segregated to explicit and implicit control processes.Methodology/Principal FindingsWe tested human subjects' ability to segregate sensorimotor signals to parallel control processes by requiring dual (explicit and implicit) control of the same reaching movement and testing for interference between these processes. Healthy control subjects were able to engage dual explicit and implicit motor control without degradation of performance compared to explicit or implicit control alone. We then asked whether segregation of explicit and implicit motor control can be selectively disrupted by studying dual-control performance in subjects with no clinically manifest neurologic deficits in the presymptomatic stage of Huntington's disease (HD). These subjects performed successfully under either explicit or implicit control alone, but were impaired in the dual-control condition.Conclusion/SignificanceThe human nervous system can exert dual control on a single action, and is therefore able to accurately segregate sensorimotor signals to explicit and implicit control. The impairment observed in the presymptomatic stage of HD points to a possible crucial contribution of the striatum to the segregation of sensorimotor signals to multiple control processes.
Highlights
We can perform most everyday movements either automatically or while paying attention to how we move
We can mindlessly reach for a light switch while walking into a room and simultaneously carry out a conversation on a mobile phone, or we can guide the same movement with full attention to this action, while doing nothing else
We recently showed that implicit motor control cannot be disengaged voluntarily during visuomotor adaptation [10]
Summary
We can perform most everyday movements either automatically or while paying attention to how we move. The action of reaching for the light switch is thought to be guided by implicit control, which is abstract and unavailable to consciousness [1,2,3,4], and which is typically engaged in ‘‘automatic’’ movements, such as steering a car. An interesting aspect of implicit control is that we are able to optionally devote attentive guidance to a movement that we can already perform automatically. This ability implies that the relationship between control processes and movement execution is not obligatory: the same movement may be guided implicitly or explicitly. This flexibility suggests that sensorimotor signals, including those that encode spatially overlapping perception and behavior, can be accurately segregated to explicit and implicit control processes
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