ADRENOCORTICOTROPIN WIDENS THE FOCUS OF ATTENTION IN HUMANS - A NONLINEAR ELECTROENCEPHALOGRAPHIC ANALYSIS

Objective: This study examined the effects of ACTH 4-10, a fragment of adrenocorticotropin (ACTH) with known central nervous system (CNS) ac tivity, on the dimensional complexity of the ongoing electroencephalog raphic (EEG) activity. Stressful stimuli cause ACTH to be released fro m the pituitary, and as a neuropeptide ACTH may concurrently exert ada ptive influences on the brain's processing of these stimuli. Previous studies have indicated an impairing influence of ACTH on selective att ention. Methods: Dimensional complexity of the EEG, which indexes the brain's way of stimulus processing, was evaluated while subjects perfo rmed tasks with different attention demands. Sixteen healthy men (23 t o 33 years) were tested once after placebo and another time after admi nistration of ACTH 4-10 (1.25 mg intravenously (TV), 30 minutes before testing). The EEG was recorded while subjects were presented with a d ichotic listening task (consisting of the concurrent presentation of t one pips to the left and right ear). Subjects either a) listened to pi ps in both ears (divided attention), or b) listened selectively to pip s in one ear (selective attention), or c) ignored all pips. Results: D imensional complexity of the EEG was higher during divided than select ive attention. ACTH significantly increased the EEG complexity during selective attention, in particular over the midfrontal cortex (F-2, C- 2). Conclusions: The effects support the view of a de-focusing action of ACTH during selective attention that could serve to improve the org anism's adaptation to stress stimuli.