The cerebellum applies an internal forward-model to predict the sensory consequences of actions. This forward-model is updated based on on-line performance monitoring. A previous study has shown that performance monitoring is altered in patients with focal vascular cerebellar lesions, but altered neural responses are not paralleled by impaired behaviour, and the critical cerebellar sites have yet to be identified. The present study investigated if saccadic performance monitoring is more severely altered in patients with cerebellar degenerative disease relative to the previously examined patients with focal vascular cerebellar lesions, and which cerebellar regions support performance monitoring. 16 patients and 16 healthy controls performed an antisaccade task while an electroencephalogram (EEG) was recorded. Error rates were increased, and the error-related negativity (ERN), an event-related potential (ERP) component associated with error processing/performance monitoring, was reduced while the error positivity (Pe), a later ERP component related to more conscious aspects of error processing, was preserved in patients. Thus, performance monitoring is altered in patients with cerebellar degeneration, confirming a critical role of the cerebellum for fast classification of saccadic accuracy. In contrast to patients with focal lesions, post-acute functional reorganization and compensation presumably is hampered by disease progression, resulting in altered neural processing and impaired behavioural performance. Voxel-based morphometry (VBM) indicated the strongest effects for behavioural performance, with correlations between gray matter volume reduction in bilateral posterolateral regions (left Crus II and right lobule VI) and increased error rates. Moreover, somewhat smaller correlations were found for volume loss in left lobule VIIb/VIIIa and right lobule V and ERN amplitude, and in right Crus I and Pe amplitude. The present findings are consistent with involvement of posterolateral cerebellar regions in motor and cognitive functions.
Keywords: Ataxia; Cerebellar degenerative disease; Cerebellum; EEG; Performance monitoring.
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