Dopaminergic and serotoninergic influence on duration discrimination and vigilance

There is some evidence from animal studies suggesting that dopamine (DA) agonists speed up a hypothesised internal clock, whereas DA antagonists such as haloperidol slow down the clock rate. Furthermore, clinical studies on haloperidol have reported significant deficits in duration discrimination performance (DD). Two double-blind balanced crossover studies with 24 healthy male volunteers each were designed to answer the following questions: 1. Do the DA agonists L-dopa and the DA antagonist haloperidol induce changes in DD? 2. Do the 5-HT uptake inhibitor fluoxetine and the 5-HT receptor antagonist ritanserin induce changes in DD? 3. Can any relationship be demonstrated between changes in DD and changes in vigilance? Haloperidol produced a marked decrease in DD, whereas for the DA agonist no changes could be demonstrated. Performance in DD was slightly improved by the 5-HT agonist and the 5-HT antagonist. Both dopaminergic and serotoninergic changes in DD seemed to be independent of the level of vigilance.