Effects of oral scopolamine on human stimulus evaluation

In a previous study of the effect of age on information processing, both age and stimulus complexity slowed reaction time (RT) and the latency of the P300 component of the brain event-related potential (ERP). The aim of the present study was to compare the effects of scopolamine (an anticholinergic) with the previously noted effects of age. The choice of scopolamine was prompted by current hypotheses concerning decline in cholinergic function with age. Twelve adult women were studied on a battery of tasks before and after scopolamine in oral doses of 0.0 (placebo), 0.6 and 1.2 mg. Reaction times (RT) and event-related potentials (ERP) were measured. The principal task was one that combined two levels of stimulus complexity and two levels of response difficulty to provide four subtasks. Scopolamine slowed RT and P300 as had age, but scopolamine slowed responses to simple stimuli more than responses to complex stimuli. Scopolamine effects on other tasks in the battery were small but consistent with an action of scopolamine on an early stimulus preprocessing stage that is independent of a stimulus evaluation stage that is also affected by age.