To investigate, using functional magnetic resonance imaging, the influence of a long-term dopaminergic therapy on brain activation during a simple motor task in early, previously untreated patients with Parkinson disease.
Thirteen patients with Parkinson disease in Hoehn-Yahr stage 1 or 2, with a right predominance of the disease, underwent functional magnetic resonance imaging during self-paced continuous right-hand tapping before and after 6 months of therapy with ropinirole 15 mg/d. The task was monitored online with a dedicated device, which measures the strength and frequency of the tapping.
All patients with Parkinson disease on ropinirole treatment showed a clinically significant improvement, and their functional magnetic resonance imaging pattern after treatment showed a reduced activation in the right postcentral (primary sensory-motor area), supramarginal and inferior parietal gyri compared with the activation pattern before treatment. No area of increased activation was observed after therapy.
In line with the classical functional deafferentation hypothesis, dopaminergic stimulation should increase motor cortex activity as a result of restoration of the striatocortical loops. On the contrary, our results challenge this hypothesis as we found decreased cerebral activity after a short-term chronic dopaminergic treatment. We suggest that the recruitment of cortical motor circuits aimed to overcome the functional deficit of the striatocortical loops lessens after dopaminergic treatment.