We studied the electrophysiological and neuropsychological effects of acute modulation of central noradrenergic (NA) transmission using a specific alpha 2-antagonist atipamezole (ATI) in sic healthy volunteers. ATI had effects on resting EEG, auditory event-related potentials and neuropsychological tests. Quantitative EEG revealed increased total power in frontal, parietal and temporo-occipital areas without significant changes in the mean or peak frequencies. Event-related potentials showed no effects on the active attention-related processing negativity or the passive mismatch negativity, but frontally recorded mean amplitude of target-P300 was decreased. Neuropsychological tests after ATI revealed improvement in Digit Span, more errors in Word Recognition task, and no effects on Moss spatial recognition task. In healthy subjects with intact NA systems and without any attention deficit, ATI produced evident NA overactivity. ATI decreased the spontaneous thalamocortical oscillation of EEG and improved focused attention (Digit Span). It impaired, however, more divided attention (decreased mean P300 amplitude, increased errors in Word Recognition).