It is well known that most movements improve with practice. However, the way the brain accomplishes this remains largely unknown. Functional magnetic resonance imaging (fMRI) has provided significant insights into brain mechanisms of cognition. In comparison, fMRI studies of motor learning and motor memory have been limited by the constrained space and the problem of unwanted head movements. As a result the great majority of fMRI studies of motor learning have investigated sequences of finger movements. To overcome these limitations, we have developed a novel MR-compatible wrist task to study two types of motor learning that undrlie our ability to accurately point to visual targets: (1) Motor skill learning - the ability to acquire new patterns of muscle activity so that movement accuracy increases without a reduction in speed. (2) Visuomotor adaptation - the ability to associate an already learned pattern of muscle activation with a new spatial goal. We will study these two types of learning with a baseline and a rotation condition, respectively. In the baseline condition, subjects make fast uncorrected pointing movements of the wrist to a series of 8 targets arrayed on a screen. Skill is the decrease in movement time (MT) and endpoint variability with practice. In the rotation condition, with the same target set, subjects initially make systematic 30? directional errors, which they reduce through adaptation. Importantly, we have developed a method that keeps MT and peak velocity constant so that any observed brain activation changes are attributable to learning and not performance changes. In addition, we will also examine the neural correlates of re-learning on a second day, differences between the dominant and non-dominant hand, mechanisms of motor interference, and degree of transfer of motor learning between arms. A better understanding of hemispheric contributions to motor learning and motor memory will offer insight into mechanisms of recovery after focal brain injury. We anticipate our approach will be applicable to patients in future studies.
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