[Refinement of an EEG diurnal vigilance index. Application to drug trials].

Theta/alpha spectral powers ratio was used to quantify physiological decrease of vigilance occurring after 5 min recording eyes closed, at different times of the day, in normal volunteers with 'high alpha'. Maximum decrease of vigilance occurred at about 2 or 4 p.m. Theta/alpha ratio fluctuations were similar on the homologous right and left scalp areas. This ratio is useful in psychopharmacology to quantify the antagonist activity of a CNS stimulant drug on the physiological decrease of vigilance after 5 min as well as the sedative effect of a drug. It allows to follow the kinetics of the drug action at receptor level.