The Brain As an Adaptive Filter: Auditory Steady State Response to Sound Stimuli Containing Binaural Beats during Human Daytime Nap

“Binaural beats” (BB) is a type of sound stimulus being studied as non-invasive tools to promote sleep. BB is a sensation occuring when two monotonous sounds of slightly different pitch are supplied to the listener’s right and left ear separately. This type of stimulation has the advantage to be perceived even at very low sound volumes essentially bordering the hearing threshold, so such a stimulus creates little disturbance to sleep. However, the patterns of its effect are difficult to study due to the weakness of electric brainwave response. The purpose of present paper is to check applicability of the brainwave entrainment hypothesis to auditory stimuli with embedded BB delivered during short-term human nap. The results demonstrate variability of auditory steady state response (ASSR) depending on BB frequency of the stimulus as well as on sleep stage that is not envisaged by the above hypothesis. It should be taken into account when predicting the effect of BB-based noninvasive sleep aids. Furthermore, the analysis of ASSR spectra allows the hypothesis to be put that the human brain falling asleep is a self-adjusting system in relation to incoming sound stimuli, for it strengthens the elements of auditory response which contribute to deepening of naturally evolving sleep.