Drug effects on EEG frequency spectra as a function of interstimulus interval.

The frequency spectra of EEG background activity preceding the stimulus in a serial simple RT task were investigated as a function of interstimulus interval (ISI). The percentage of power in the alpha and theta bands increased with longer ISIs while the delta activity decreased. Additionally, the effects of an amphetamine and a barbiturate were investigated. The increase in alpha activity with longer ISI conditions were larger after barbiturate than after placebo, while it remained constant after amphetamine treatment. Contrary to expectation, no systemic changes in alpha activity were found during the 3-h session for any of the treatments. It is suggested that the background EEG during the foreperiod of an RT task mainly reflects phasic arousal. The characteristics of the background EEG in the present experimental situation may be quite different from that recorded under "relaxed" no-task conditions.