Intact motor sequence learning but altered error-related brain activation in writer's cramp

Writer's cramp (WC) is a task-specific arm dystonia with involuntary contractions during writing. While motor circuit dysfunction is well-characterized in WC, the roles of motor learning and error processing remain unclear. We investigated implicit motor sequence learning in WC patients using fMRI during Serial Reaction Time Task (SRTT), focusing on cerebellar activity and error-related processing. 25 WC patients and 17 healthy controls were compared. Both groups showed a comparable sequence-specific advantage with faster reaction times and lower error rates in sequence versus random blocks. WC patients showed significantly higher combined error rates than controls, whereas group differences in reaction time did not reach significance. Speed-accuracy analysis revealed greater accuracy deterioration during fast responses in WC patients. Error trials elicited increased cerebellar activation (right lobule VIII, left lobule IX) in patients. Exploratory analysis revealed absent amygdala deactivation in patients during errors, contrasting the suppression observed in controls, an effect that did not survive whole-brain correction. Our findings indicate preserved implicit sequence learning alongside reduced accuracy of motor execution in WC, particularly under speed demands. Altered cerebellar and amygdala error responses suggest that WC pathophysiology extends beyond traditional motor networks, encompassing disrupted error salience processing.