Age-Related Shift Towards Feedforward Motor Control Under Uncertainty

Humans perform movements in the face of uncertainty on a daily basis. To accomplish these tasks without error, young adults frequently rely on feedback-mediated motor strategies that allow them to update their movement as certainty evolves. However, it remains unclear how aging impacts the ability to plan and execute movement under uncertain conditions. To investigate how aging affects the ability to plan actions under uncertainty, we designed a “go-before-you-know” (GBYK) reaching task in which we varied certainty by changing the probability that a reach target would be correct. Fifteen healthy young adults and fifteen older adults completed this task while undergoing fMRI. Behaviorally, young adults employed a strategy consistent with feedback-mediated control, biasing their reach trajectories toward the more likely target when uncertainty was low, and intermediate to potential targets when uncertainty was high. Older adults employed a different approach, characterized by a pronounced rightward bias, particularly under high uncertainty, suggesting a shift toward feedforward control. Neuroimaging results mirrored these behavioral patterns, revealing that young adults encoded task certainty and reach direction in sensorimotor regions more strongly than older adults. Overall, these findings suggest that aging diminishes the ability to flexibly encode task-related uncertainty, resulting in a shift towards feedforward control strategies.