Theta and beta BBs are of particular interest since they may cause states of relaxation and attentiveness, respectively, which are opposite mental states so that they can be easily compared.
Tone frequencies stimuli between 450 and 500 Hz are recommended ( García Argibay, 2018). In theory, each BB produces neural oscillations at the corresponding EEG frequency band, inducing the associated mental state. For each EEG frequency band, the following corresponding BB can be generated: (1) delta BB, theta BB, alpha BB, beta BB, and gamma BB. In terms of EEG frequency bands, BB has a frequency difference within the band range of interest. Normally, 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). Neurons oscillate in several well-known EEG frequency bands. This effect was coined as Frequency Following Response (FFR Marsh and Worden, 1968 Worden and Marsh, 1968). 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. Later, Worden and Marsh (1968) were investigating about electrophysiological effects of sound on the brain. 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). 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). In conclusion, neural resynchronization was met with both personalized theta and beta BB, but no different mental conditions seemed to be achieved.
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. 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. This power change seems to be related to auditory perception and sound location. Results showed larger absolute power differences for both BB stimulation sessions than resting state on bilateral temporal and parietal regions. 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. 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. The adjustable frequencies were estimated for each participant in accordance with their heart rate by applying the Brain-Body Coupling Theorem postulated by Klimesch. 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 f c for theta EEG band was 4.60 Hz ± 0.70 SD) and beta BB (since f c for beta EEG band was 18.42 Hz ± 2.82 SD). The aim of this research was to investigate whether personalized BB (specifically those within theta and beta EEG bands) improve brain entrainment. This auditory stimulation has been widely used to module brain rhythms and thus inducing the mental condition associated with the EEG bandwidth in use.
Escuela de Ingeniería y Ciencias, Tecnológico de Monterrey, Monterrey, Mexicoīinaural 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.Corona-González * Luz María Alonso-Valerdi David I.
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