Adrenocorticotropin-related modulation of the human EEG and individual variability.

During a 6-h period in resting conditions, the blood concentrations at rest of cortisol, glucose and the adrenocorticotropic hormone (ACTH) varied spontaneously within physiological ranges in eight healthy male volunteers (24.5+/-1.7 years), without pulsatile changes, correlation among variables, or indications of stress response. The power of the 6.5-14.0 Hz physiological 'alpha' rhythm of the electroencephalogram (EEG) proved inverted-U correlated with the ACTH concentration (with maximum power at 12-14 pmol/l ACTH) but was independent from the extent of ACTH change or from cortisol/glucose concentrations. Two subgroups of subjects with low/high EEG power values could be separated depending on ACTH concentration, with estimated cut-off at 7-8 pmol/l. A direct ACTH modulation of brain electrophysiology or common factors (e.g. the corticotropin-releasing hormone) pacing both ACTH and EEG are suggested and may account for individual EEG differences.