Abstract
Binaural beats (BB) consist of two slightly distinct auditory frequencies (one in each ear), which are differentiated with clinical electroencephalographic (EEG) bandwidths, namely, delta, theta, alpha, beta, or gamma. This auditory stimulation has been widely used to module brain rhythms and thus inducing the mental condition associated with the EEG bandwidth in use. The aim of this research was to investigate whether personalized BB (specifically those within theta and beta EEG bands) improve brain entrainment. Personalized BB consisted of pure tones with a carrier tone of 500 Hz in the left ear together with an adjustable frequency in the right ear that was defined for theta BB (since fc for theta EEG band was 4.60 Hz ± 0.70 SD) and beta BB (since fc for beta EEG band was 18.42 Hz ± 2.82 SD). The adjustable frequencies were estimated for each participant in accordance with their heart rate by applying the Brain-Body Coupling Theorem postulated by Klimesch. To achieve this aim, 20 healthy volunteers were stimulated with their personalized theta and beta BB for 20 min and their EEG signals were collected with 22 channels. EEG analysis was based on the comparison of power spectral density among three mental conditions: (1) theta BB stimulation, (2) beta BB stimulation, and (3) resting state. Results showed larger absolute power differences for both BB stimulation sessions than resting state on bilateral temporal and parietal regions. This power change seems to be related to auditory perception and sound location. However, no significant differences were found between theta and beta BB sessions when it was expected to achieve different brain entrainments, since theta and beta BB induce relaxation and readiness, respectively. In addition, relative power analysis (theta BB/resting state) revealed alpha band desynchronization in the parieto-occipital region when volunteers listened to theta BB, suggesting that participants felt uncomfortable. In conclusion, neural resynchronization was met with both personalized theta and beta BB, but no different mental conditions seemed to be achieved.
Highlights
In 1839, Heinrich Wilhelm Dove found that providing two slightly different tone frequencies, one in each ear, were perceived as a third phantom frequency depicted by the difference of these two frequencies, which was called binaural beats (BB; Keeley, 2006)
It was until the 1950’s when Robert Monroe formally started to research the clinical application of BB, establishing that the dissimilarity of both frequencies must be within the electroencephalographic (EEG) spectrum, that brain entrainment could be elicited (Berger and Turow, 2011)
Delta band is present while deep sleep; theta band is in extremely relaxation, drowsiness, or meditation; alpha is best seen at rest with eyes closed; beta is present during problem solving and focusing; and gamma is characterized by cognitive and motor functions (Siuly et al, 2016)
Summary
In 1839, Heinrich Wilhelm Dove found that providing two slightly different tone frequencies, one in each ear, were perceived as a third phantom frequency depicted by the difference of these two frequencies, which was called binaural beats (BB; Keeley, 2006) It was until the 1950’s when Robert Monroe formally started to research the clinical application of BB, establishing that the dissimilarity of both frequencies must be within the electroencephalographic (EEG) spectrum, that brain entrainment could be elicited (Berger and Turow, 2011). Worden and Marsh (1968) were investigating about electrophysiological effects of sound on the brain They found that an auditory stimulus provokes a synchronous-neural evoked response which reproduces the frequency and waveform of the incoming stimulus throughout the central auditory pathway. Neurons oscillate in several well-known EEG frequency bands These are delta (δ = 0.1–4 Hz), theta (θ = 4–8 Hz), alpha (α = 8– 13 Hz), beta (β = 13–30 Hz), and gamma (γ > 30 Hz). Tone frequencies stimuli between 450 and 500 Hz are recommended (García Argibay, 2018)
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