Why is the explicit component of motor adaptation limited in elderly adults?

The cognitive component of motor adaptation declines with aging. Yet, in other motor tasks, older adults appear to rely on cognition to improve their motor performance. It is unknown why older adults are not able to do so in motor adaptation. To solve this apparent contradiction, we tested the possibility that older adults require more cognitive resources in unperturbed reaching compared with younger adults, which leaves fewer resources available for the cognitive aspect of motor adaptation. Two cognitive-motor dual-task experiments were designed to test this. The cognitive load of unperturbed reaching was assessed via dual-task costs during the baseline period of visuomotor rotation experiments, which provided us with an estimation of the amount of cognitive resources used during unperturbed reaching. However, we did not observe a link between dual-task costs and explicit adaptation in both experiments and, therefore, failed to confirm this hypothesis. Instead, we observed that explicit adaptation was mainly associated with visuospatial working memory capacity. This suggests that visuospatial working memory of an individual might be linked to the extent of explicit adaptation for young and older adults.NEW & NOTEWORTHY Our work addresses the contradiction between the age-related increase in the contribution of cognition for the execution of motor tasks and the age-related decrease in the cognitive component of motor adaptation. We predicted that elderly adults would need more cognitive resources for reaches and would, therefore, not have enough cognitive resources available for adaptation. Rather, we observed that visuospatial abilities could better explain the amount of cognition used by our participants for motor adaptation.