Dopaminergic modulation of amygdala activity during emotion recognition in patients with Parkinson disease

Variable findings have been reported for emotional processing in patients with Parkinson disease (PD). These contradictions could be due to differences in the progression of dopamine (DA) depletion. Levodopa treatment could have either beneficial or detrimental effects on brain functions modulated by DA according to disease progression. In healthy subjects, levodopa administration leads to a decreased amygdala activation in response to emotional tasks. Because it is known that there is a link between DA loss in mesolimbic system and depression, we hypothesized that PD patients without depression would have spared limbic DA projections. Consequently, levodopa medication could overdose limbic regions relative to severe dorsal striatal denervation. To evaluate the effect of levodopa on amygdala activation, we conducted a functional magnetic resonance imaging study in nondemented, nondepressed PD patients compared with healthy volunteers. Patients with PD and healthy subjects received either levodopa or placebo in 2 functional magnetic resonance imaging sessions. Amygdala activation was evaluated during a facial emotion recognition task. A similar right-amygdala activity was seen in both healthy subjects and PD patients in the placebo session. After levodopa administration, activity was reduced in both groups. In the patients, the levodopa dose used significantly improved motor dysfunction. Nondemented, nondepressed PD patients thus seem to have relatively preserved DA mesolimbic projections, and consequently, the same dose of levodopa needed to correct the lack of DA in the severely depleted putamen (motor part of striatum) would incidentally overdose the mesolimbic projections toward the amygdala.