Biological rhythms in arousal indices: a potential confounding effect in EEG biofeedback.

Abstract

ABSTRACTSeveral investigators have observed ultradian rhythmicities in physiological indices of arousal. Although EEG biofeedback has been widely explored as a means of auto‐regulating cortical arousal, alpha or theta enhancement has not yet been convincingly demonstrated in comparison to continuous baseline controls for the possible effect of endogenous cyclical arousal trends. Diurnal EEG and subjectively appraised arousal measures were recorded from 11 subjects on a 5‐min recording, 5‐min recovery schedule, continuously over 7 1/2 hrs. Subjects returned to the laboratory for an equal amount of recording during which they attempted to either raise or lower the frequency of their EEG with the aid of biofeedback. Significant ultradian rhythmicity centered at about 200 min/cycle was observed in EEG measures and in subjectively appraised arousal. Although eyes‐open frequency‐raising and frequency‐lowering biofeedback training was efficacious in comparison to long‐day baselines, eyes‐closed frequency‐lowering training was not, lending support to other studies which have failed to achieve overall eyes‐closed alpha or theta enhancement even with many hours of training. Because the observed ultradian and circadian EEG rhythmicities could be spuriously interpreted as learning curves under a biofeedback paradigm, it is argued that future designs should incorporate continuous baseline controls.