Effects of levodopa on motor sequence learning in Parkinson's disease

Dopaminergic therapy with levodopa improves motor function in PD patients, but the effects of levodopa on cognition in PD remain uncertain.

To use H(2)(15)O and PET to assess the effect of levodopa infusion on motor sequence learning in PD.

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.

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).

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.