Pharmacologically induced changes in arousal: effects on behavioral and electrophysiologic measures of alertness and attention.

The relationships between the diffuse subcortical neurotransmitter systems and behavioral and physiologic measures of alertness and attention are not well understood. This study was designed to further understand these relationships. In this double-blind experiment, 23 subjects ingested methylphenidate, diphenhydramine or placebo on 3 different days and performed behavioral and cognitive tasks including covert orienting of spatial attention and visual search tasks. Subjective and physiologic measures of alertness included EEG frequency analysis, EEG event-related desynchronization, and amount of sleep and sleep onset time in the unstimulated eyes closed state. Performance on the cognitive tasks improved with MP and worsened with DPHA, but there were no specific attentional effects. The best measures of alertness were based on self-rated scales and on EEG recorded in the unstimulated eyes closed state. These observations suggest that methylphenidate and diphenhydramine primarily affected overall state and that healthy humans were able to partially compensate for the pharmacologically induced alertness changes during cognitive task performance.