Amygdala activation modulated by levodopa during emotional recognition processing in healthy volunteers: a double-blind, placebo-controlled study.

A critical role of dopaminergic systems in emotional processing has been revealed by several animal and clinical studies in Parkinson disease and schizophrenia. We conducted a study with functional magnetic resonance imaging (fMRI) in 13 healthy volunteers to test the dopaminergic modulation on amygdala response to emotional processing and to evaluate if it was the result of a direct action on amygdalar nuclei or indirect modulation via medial prefrontal cortex projecting on amygdala.A placebo-controlled crossover experimental design was used. Subjects received either levodopa (100 mg) or placebo in 2 fMRI sessions. Amygdala activation was evaluated during a facial emotion recognition test.The statistical comparison between placebo versus levodopa situations revealed a significant reduction in activation of right amygdala during the levodopa fMRI session. The functional connectivity analysis revealed only a change of correlated activations between right and left amygdala, and not medial prefrontal cortex, after levodopa administration. Our results suggest that administration of levodopa to healthy volunteers impairs the amygdalar activation. It supports the hypothesis that amygdala activation follows an inverted U-shaped curve in relation to dopamine (DA) concentration. The results of the functional connectivity seem to suggest a dopaminergic action on amygdalar nuclei rather than a modulation of medial prefrontal cortex on amygdala.