Dopamine and human information processing: a reaction-time analysis of the effect of levodopa in healthy subjects.
BACKGROUND
Dopamine is involved in a variety of motor and non-motor information-processing operations. One way to determine its contribution to human information processing is to study reaction time (RT) performance after oral absorption of its precursor, levodopa, which increases its concentration in the nervous system.


OBJECTIVE
The purpose of the present study was to investigate the effect of a single dose of levodopa on information processing in healthy human subjects using the additive-factor method. After oral absorption of a single dose of levodopa (200 mg) or a placebo (randomized, double-blind, cross-over design), eight adults (aged 21-28 years, mean 25 years) performed a two-choice visual RT task. Signal intensity, stimulus-response mapping and foreperiod duration were manipulated.


RESULTS
The effects of these three variables were found additive on RT, indicating that that three independent stages - namely, stimulus preprocessing, response selection and motor adjustment - were manipulated. Levodopa improved RT performance in a specific way: it interacted with signal intensity but its effect was additive with those of stimulus-response mapping and foreperiod duration.


CONCLUSIONS
These results show that levodopa specifically affects the stimulus preprocessing stage, which suggests that the dopaminergic system plays a role in sensory processing, possibly by acting on the level of arousal.
Centre de Recherches en Neurosciences Cognitives, Centre National de la Recherche Scientifique, 31 Chemin Joseph Aiguier, 13402 Marseille Cedex 20, France.
Philippe
P
Rihet
Camille-Aimé
CA
Possamaï
Joëlle
J
Micallef-Roll
Olivier
O
Blin
Thierry
T
Hasbroucq
D000328:Adult; D000978:Antiparkinson Agents / Q000494:pharmacology; D065105:Aromatic Amino Acid Decarboxylase Inhibitors; D001545:Benserazide / Q000494:pharmacology; D018592:Cross-Over Studies; D004298:Dopamine / Q000502:physiology*; D015259:Dopamine Agents / Q000494:pharmacology*; D004311:Double-Blind Method; D004576:Electromyography; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005260:Female; D006801:Humans; D007980:Levodopa / Q000494:pharmacology*; D008297:Male; D008606:Mental Processes / Q000187:drug effects*; D011597:Psychomotor Performance / Q000187:drug effects; D011930:Reaction Time / Q000187:drug effects*
D000978:Antiparkinson Agents; D065105:Aromatic Amino Acid Decarboxylase Inhibitors; D015259:Dopamine Agents; D004791:Enzyme Inhibitors; D007980:Levodopa; D001545:Benserazide; D004298:Dopamine