Effects of caffeine and diphenhydramine on auditory evoked cortical potentials.

Caffeine and diphenhydramine are known to affect cognitive functioning in vigilance tasks. In this study, long-latency auditory evoked potentials (AEPs) obtained during concomitant performance of a visual vigilance task were examined for changes in response to administration of caffeine (200 mg) and diphenhydramine (25 mg). The AEPs were also analyzed for changes over time for up to two hours postdrug administration. Significant increases in N1 and P2 latencies and decreases in amplitude voltage were exhibited over time. The P2-N2 amplitude was significantly lower throughout testing after taking caffeine. A significant increase was seen in the P2-N2 amplitude 40 min. after diphenhydramine ingestion. These changes in amplitude may be the result of the auditory stimulus acting as a diversion to the participants while performing the visual vigilance task. Diphenhydramine was more likely to impair participants' vigilance, resulting in greater attention paid toward the auditory stimulus, whereas caffeine seemed to help participants maintain their focus of attention on the visual vigilance task.