Abstract

EFFECTS OF SCOPOLAMINE AND NICOTINE ON ENCODING IN CHOICE REACTION TIME TASKS

*Andrew P. Smith, PhD

ABSTRACT

Background: There has been considerable interest in the role of the cholinergic system in attention and response. This has often involved challenges with scopolamine or nicotine. The present study extended the literature by examining the effects of these two drugs on encoding and response to new information. Method: Twenty male university students who were light smokers were recruited. The experiment involved a repeated measures design, with each participant completing five experimental sessions at weekly intervals. Over the five sessions, each participant received one of each of the following: scopolamine vehicle + 0.75 mg nicotine; scopolamine vehicle + 1.5 mg nicotine; 1.2 mg scopolamine + nicotine vehicle; 1.2 mg scopolamine +1.5 mg nicotine; and scopolamine vehicle + nicotine vehicle. In each session, participants carried out a pre-drug baseline and post-drug test. The
performance tasks involved choice reaction times with focused attention and categoric search. Results: Relative to placebo, the scopolamine-induced impairment in response time was restricted to conditions in which the stimulus was different from the previous trial, with the size of the decrement being the same for both focused and search tasks. Nicotine improved response time on both alternating and repeated stimulus trials, with the size of the effect being similar to scopolamine on the focused task but considerably smaller on the search task. In the combined treatment, 1.5mg nicotine reduced but did not eliminate the scopolamine-induced deficit; the deficit was reduced by around 50% in both the search and the focused tasks in the alternated stimulus conditions impaired by scopolamine administration. Conclusion: Both scopolamine and nicotine had significant effects on choice reaction time. The profile of the two drugs was different, and nicotine only partially removed the scopolamine-induced impairments. Such effects may underlie changes in encoding observed in other changes of state, such as the effects of caffeine.

Keywords: Scopolamine; Nicotine; Focused attention; Categoric search; Choice Reaction time; Encoding; Alternations; Repeats.