Brain Responses to a 6-Hz Binaural Beat: Effects on General Theta Rhythm and Frontal Midline Theta Activity.

Nantawachara Jirakittayakorn,Yodchanan Wongsawat

doi:10.3389/fnins.2017.00365

Abstract

A binaural beat is a beat phenomenon that is generated by the dichotic presentation of two almost equivalent pure tones but with slightly different frequencies. The brain responses to binaural beats remain controversial; therefore, the aim of this study was to investigate theta activity responses to a binaural beat by controlling factors affecting localization, including beat frequency, carrier tone frequency, exposure duration, and recording procedure. Exposure to a 6-Hz binaural beat on a 250 Hz carrier tone for 30 min was utilized in this study. Quantitative electroencephalography (QEEG) was utilized as the recording modality. Twenty-eight participants were divided into experimental and control groups. Emotional states were evaluated by Brunel Mood Scale (BRMUS) before and after exposing to the stimulus. The results showed that theta activity was induced in the entire cortex within 10 min of exposure to the stimulus in the experimental group. Compared to the control group, theta activity was also induced at the frontal and parietal-central regions, which included the Fz position, and left hemisphere dominance was presented for other exposure durations. The pattern recorded for 10 min of exposure appeared to be brain functions of a meditative state. Moreover, tension factor of BRUMS was decreased in experimental group compared to control group which resembled the meditation effect. Thus, a 6-Hz binaural beat on a 250 Hz carrier tone was suggested as a stimulus for inducing a meditative state.

Highlights

The dichotic presentation of two almost equivalent pure tones but with slightly different frequencies leads to perceive fluctuations sounds which occurs as amplitude modulation generated by the two pure tones, or so-called beat, in the brain
A 6-Hz binaural beat was presented to the experimental group, and silence was presented to the control group
Several factors including beat frequency, carrier tone frequency, exposure duration, and recording procedures interfere with the discussion process, as these factors affect brain responses, and differences in these factors do not allow for clear comparisons among studies

Summary

Introduction

The dichotic presentation of two almost equivalent pure tones but with slightly different frequencies leads to perceive fluctuations sounds which occurs as amplitude modulation generated by the two pure tones, or so-called beat, in the brain. The beat in this phenomenon is generated within the brain and is referred to as a binaural beat. The fluctuation in frequency equals the difference in the two pure tones that are presented. A classic study reported that the maximum difference in the two tones for which humans can perceive them as beat is 35 Hz; otherwise, 2 separate pure tones were perceived instead (Oster, 1973).

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