A low dose of subcutaneous nicotine improves information processing in non-smokers

Many studies have found that cigarette smoking or nicotine improves mental functioning in abstinent smokers. An unresolved issue is whether this improvement is due primarily to a direct facilitation of performance or to relief of the impairment caused by nicotine withdrawal. We evaluated the performance of 12 non-smokers before and twice (15 and 45 min) after a subcutaneous injection of 0.8 mg nicotine, 0.8 ml saline, and a control no treatment, on a choice reaction time (RT) task. Each treatment was given on a separate day; the control day was given on the first session. The order of nicotine and saline was balanced between subjects, and injections were given double-blind. The RT task manipulated stimulus and response processing. These manipulations consisted of two levels of stimulus complexity and two levels of response complexity, resulting in four task conditions. These manipulations along with latency measures of the event-related potential were used to identify the components of processing that mediated nicotine's effects on performance. During each active drug session blood nicotine levels, cardiovascular, and subjective responses were measured before and after each of the three tests (pre-drug, 15 min and 45 min post-drug). For the information processing measures only the comparisons of the pre- and 15-min post-test showed significant drug effects. Nicotine compared to saline significantly increased the number of responses at the fast end of the RT distribution. However, there were no changes in accuracy. Nicotine also speeded mean RT compared with saline or the control day, but the effects were only significant for the control-nicotine comparison. There was an interaction between effects of nicotine and the task variables, such that nicotine speeded P3 latency in the hardest task condition, while slowing it in the other task conditions. Nicotine significantly increased heart rate, which lasted for the entire session. Blood nicotine levels were lower than expected from a preliminary study in smokers and may have been responsible for the smaller than expected mean RT effects. These findings suggest that even a low dose of nicotine directly affects attention or stimulus processing components of information processing. This study also illustrates the importance of assessing both multiple components of information processing and nicotine levels when examining the effects of nicotine on cognition.