Background: Dopaminergic therapy with levodopa improves motor function in PD patients, but the effects of levodopa on cognition in PD remain uncertain.
Objective: To use H(2)(15)O and PET to assess the effect of levodopa infusion on motor sequence learning in PD.
Methods: Seven right-handed PD patients were scanned "on" and "off" levodopa while performing a sequence learning task. The changes in learning performance and regional brain activation that occurred during this intervention were assessed.
Results: During PET imaging, levodopa infusion reduced learning performance as measured by subject report (p < 0.05). This behavioral change was accompanied by enhanced activation during treatment in the right premotor cortex and a decline in the ipsilateral occipital association area (p < 0.01). Levodopa-induced changes in learning-related activation responses in the occipital association cortex correlated with changes in learning indexes (p < 0.01).
Conclusions: Levodopa treatment appears to have subtle detrimental effects on cognitive function in nondemented PD patients. These effects may be mediated through an impairment in brain activation in occipital association cortex.