Bilaterally Synchronous Ultradian EEG Rhythms In Awake Adult Humans

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Abstract
The study documents the presence of ultradian 90‐min variations in the daytime EEG, Eight adult subjects were recorded in an isolation chamber for 8 hrs (0930‐1730). Referential frontal (F3 and F4) and parietal (P3 and P4) EEGs were obtained and frequency analyzed every 15 min for a duration of 100 s with eyes open. Behavioral and psychological data were also gathered. Spectral analyses showed the presence of significant 16 c/day (72‐120 min) rhythms at Kieitman's basic‐rest‐activity‐cycle (BRAC) rate in the overall EEG (4‐20 Hz) of each hemisphere. These electro‐cortical fluctuations were in phase between the two hemispheres. They peaked significantly only at the frontal sites. For individual EEG bandwidths, only right frontal theta showed a marked, though not statistically significant, ultradian rhythm at the 16 c/day frequency. Substantial 8 c/day peaks were also observed. Individual differences may have accounted for the observed variability of the intensity of this BRAC‐frequency rhythm. Subjects showing greater 90‐min rhythmicity in their EEG were in general less emotionally stable on the Eysenck neuroticism subscale and considered themselves as poorer sleepers. The present findings suggest that these 90‐min fluctuations may reflect periodic oscillations in the brainstem arousal system(s).