Reductions in endogenous dopamine and reduced dopamine binding associated with loss of dopaminergic receptors due to disease progression may impair motor learning in people with PD. Conflicting evidence suggests that impaired motor learning in PD is due on the one hand to the absence of dopamine but on the other hand to "overdosing" of the basal ganglia with dopamine replacement therapy which suppresses activation of the associative striatum during the early acquisition stages of motor learning.