Diurnal periodicity of the human vertex potential.

Averaged auditory evoked potential waveforms were recorded from the vertex of human subjects 3, 9, and 15 hr. after awakening. Responses to pure tones of 60 and 80 dB SL were obtained at each session. Amplitude measures of N1-P2 and P2-N2 components were largest in the morning followed by a gradual attenuation across sessions. Waveforms amplitude during the late evening ranged from 85% to 91% of the morning amplitude.