F. Holmes Atwater

Abstract

This paper describes two studies. A first study measured the neural accommodation (changes in ongoing or overall brainwave activity) associated with complex binaural-beat stimuli. A second study, based on the same protocol, measured changes in ongoing brainwave activity associated with placebo stimuli.

A weak EEG frequency-following response to binaural beating and other rhythmic stimuli manifests using time-domain averaging brainwave analysis techniques. Theoretically, this frequency-following response emerges as a low-amplitude linked series of evoked-potential responses. It is important to note that these studies examined ongoing brainwave activity (in this case, central delta and occipital alpha) and not the frequency-following response.

Results of the two studies showed that during the binaural beat stimuli, reductions in the percentages of occipital alpha (bipolar O1-O2) were significant (individually, p < .05 and together, p < .001) during five of six free-running EEG recording periods compared to baselines. During these same recording periods reductions in the percentages of central delta (bipolar C3-C4) were similarly significant during four of six periods compared to baselines. Alpha- and delta-brainwave changes were non-significant during the placebo stimuli.

The extended reticular-thalamic activating system (ERTAS) may be the neural mechanism behind the observed brainwave changes. The reticular formation of the brain stimulating the thalamus and cortex (referred to as the ERTAS) governs cortical brainwave patterns. Acetylcholine, provided via cortico-thalamic projections, either inhibits or excites areas of the cortex by neutralizing or enhancing the effects of noradrenaline and serotonin coming to the cortex via “fountains” from the locus coeruleus and the raphe nuclei.