Compensatory cortical mechanisms in Parkinson's disease evidenced with fMRI during the performance of pre-learned sequential movements.

We used fMRI to study brain activity associated with the performance of a pre-learned sequence of complex movements of the hand-made unimanually in a group of 13 Parkinson's disease patients and a group of 11 control volunteers. Patients were scanned "off" medication. In controls, sequential movements led to the activation of bilateral sensorimotor and premotor cortex, bilateral inferior parietal cortex, supplementary motor area, bilateral putamen and globus pallidus, and the left ventral lateral nucleus of the thalamus. Sequential movements in the Parkinson's disease group were associated with a similar pattern of activation, although relative decrease of activation in striatum and thalamic areas was observed. Patients in comparison with controls showed a hyperactivation in ipsilateral premotor areas and a hypoactivation in structures of the frontostriatal motor loop. Furthermore, patient scores in the motor scale of the UPDRS correlated positively with the activation thalamus and motor cortical areas during the sequential motor task. We concluded that in Parkinson's disease there is a compensatory mechanism of the dopamine deficit in frontostriatal motor circuits that increases participation in the execution of motor tasks of parietal-lateral premotor circuits.