title: Dopaminergic neuromodulation of semantic processing: a 4-T FMRI study with levodopa.
abstract: There is emerging evidence that alterations in dopaminergic transmission can influence semantic processing, yet the neural mechanisms involved are unknown. The influence of levodopa (L-DOPA) on semantic priming was investigated in healthy individuals (n = 20) using event-related functional magnetic resonance imaging with a randomized, double-blind crossover design. Critical prime-target pairs consisted of a lexical ambiguity prime and 1) a target related to the dominant meaning of the prime (e.g., bank-money), 2) a target related to the subordinate meaning (e.g., fence-sword), or 3) an unrelated target (e.g., ball-desk). Behavioral data showed that both dominant and subordinate meanings were primed on placebo. In contrast, there was preserved priming of dominant meanings and no significant priming of subordinate meanings on L-DOPA, the latter associated with decreased anterior cingulate and dorsal prefrontal cortex activity. Dominant meaning activation on L-DOPA was associated with increased activity in the left rolandic operculum and left middle temporal gyrus. These findings suggest that L-DOPA enhances frequency-based semantic focus via prefrontal and temporal modulation of automatic semantic priming and through engagement of anterior cingulate mechanisms supporting attentional/controlled priming.
authors.affiliation: Language Neuroscience Laboratory, The University of Queensland, Brisbane, Queensland 4072, Australia.
authors.forename: David A
authors.initials: DA
authors.lastname: Copland
authors.forename: Katie L
authors.initials: KL
authors.lastname: McMahon
authors.forename: Peter A
authors.initials: PA
authors.lastname: Silburn
authors.forename: Greig I
authors.initials: GI
authors.lastname: de Zubicaray