Reduced striatal activation in response to rewarding motor performance feedback after stroke

INTRODUCTION Motor skill learning can help stroke survivors to cope with motor function deficits but requires many repetitions. One factor that keeps patients motivated is obtaining reward upon successfully completing a motor task. It has been suggested that stroke survivors have deficits in reward processing which may negatively impact skill learning. OBJECTIVE To test the hypothesis that stroke survivors have deficient reward processing during motor skill learning evident in reduced activation in the striatum and its subdivisions in functional magnetic resonance imaging as compared with healthy, age-matched control subjects. METHODS Striatal activity in response to performance dependent feedback and monetary reward was measured in 28 subacute stroke patients and 18 age-matched healthy control subjects during the training of visuomotor tracking an arc-shaped trajectory using the wrist (unimpaired side in patients, dominant side in controls) in an fMRI scanner. RESULTS Despite comparable monetary rewards, stroke patients showed reduced activation in the ventral part (p < 0.01), but not in the dorsal part of the striatum (p = 0.11). 14 patients had their lesion extending into the striatum. The nucleus accumbens as part of the ventral striatum was unlesioned in all participants and still showed a marked hypoactivation in stroke patients as compared with controls (p < 0.001), a finding that could not be explained by motivational differences between the groups. CONCLUSION Striatal hypoactivation in stroke survivors may cause impaired consolidation of motor skills. Stronger rewarding stimuli or drug-mediated enhancement may be needed to normalize reward processing after stroke with positive effects on recovery.