Effects of clonidine and scopolamine on multiple target detection in rapid serial visual presentation.

Rationale: The specific role of neuromodulator systems in regulating rapid fluctuations of attention is still poorly understood.

Objectives: In this study, we examined the effects of clonidine and scopolamine on multiple target detection in a rapid serial visual presentation task to assess the role of the central noradrenergic and cholinergic systems in temporal attention.

Method: Eighteen healthy volunteers took part in a crossover double-dummy study in which they received clonidine (150/175 μg), scopolamine (1.2 mg), and placebo by mouth in counterbalanced order. A dual-target attentional blink task was administered at 120 min after scopolamine intake and 180 min after clonidine intake. The electroencephalogram was measured during task performance.

Results: Clonidine and scopolamine both impaired detection of the first target (T1). For clonidine, this impairment was accompanied by decreased amplitudes of the P2 and P3 components of the event-related potential. The drugs did not impair second-target (T2) detection, except if T2 was presented immediately after T1. The attentional blink for T2 was not affected, in line with a previous study that found no effect of clonidine on the attentional blink.

Conclusions: These and other results suggest that clonidine and scopolamine may impair temporal attention through a decrease in tonic alertness and that this decrease in alertness can be temporarily compensated by a phasic alerting response to a salient stimulus. The comparable behavioral effects of clonidine and scopolamine are consistent with animal studies indicating close interactions between the noradrenergic and cholinergic neuromodulator systems.