Contributions of Spatial Working Memory to Visuomotor Adaptation.

Abstract

Previous studies of motor learning have described the importance of cognitive processes during the early stages of learning. However, it remains unclear which cognitive processes contribute. In this dissertation, I test the role of one particular cognitive subsystem in the motor learning process, spatial working memory (SWM). This was tested through i) behavioral correlations between the rate of learning on a visuomotor adaptation task and SWM measures, and ii) confirming overlapping neural substrates between the two types of tasks using functional magnetic resonance imaging (fMRI). In the first study, I found that young adults’ performance on a behavioral test of SWM involving mental rotation correlated with the rate of early, but not late, visuomotor adaptation. In addition, participants showed overlapping brain activation during a SWM task and the early adaptation period in regions previously identified in other SWM and visuomotor adaptation studies. A similar analysis performed with the late phase of adaptation produced no commonly activated regions. These findings suggest that the early phase of visuomotor adaptation engages SWM processes related to mental rotation. It is well documented that both cognitive and motor learning abilities decline with normative aging. However, it is unclear whether age-related declines in SWM can partially explain age-related deficits in visuomotor adaptation. A group of older adults were tested using the same methodologies as in the first study, with their results then compared to the young adults’ findings. Older adults showed a less steep learning curve for the visuomotor adaptation task than young adults, and were also less accurate on each SWM task. Unlike the young adults, older adults’ early rate of adaptation did not correlate with SWM performance. Both groups showed very similar activation for the SWM task; however, older adults did not show neural activation overlap at the early (or late) visuomotor adaptation period. A pooled group partial correlation controlling for age revealed that a steeper early rate of adaptation was associated with increased activation in a brain region associated with SWM. These findings suggest that the effective engagement of SWM processes helps explain age-related differences in visuomotor adaptation.