Short-term motor plasticity revealed in a visuomotor decision-making task

Selecting and executing an action toward only one object in our complex environments presents the visuomotor system with a significant challenge. To overcome this problem, the motor system is thought to simultaneously encode multiple motor plans, which then compete for selection. The decision between motor plans is influenced both by incoming sensory information and previous experience-which itself is comprised of long-term (e.g. weeks, months) and recent (seconds, minutes, hours) information. In this study, we were interested in how the recent trial-to-trial visuomotor experience would be factored into upcoming movement decisions made between competing potential targets. To this aim, we used a unique rapid reaching task to investigate how reach trajectories would be spatially influenced by previous decisions. Our task required subjects to initiate speeded reaches toward multiple potential targets before one was cued in-flight. A novel statistical analysis of the reach trajectories revealed that in cases of target uncertainty, subjects initiated a spatially averaged trajectory toward the midpoint of potential target locations before correcting to the selected target location. Interestingly, when the same target location was consecutively cued, reaches were biased toward that location on the next trial and this effect accumulated across trials. Beyond providing supporting evidence that potential reach locations are encoded and compete in parallel, our results strongly suggest that this motor competition is biased by recent trial history.