Short and Long term Investigation of Brainwave Entrainment induced by Binaural Beats: A Multivariate EEG Analysis and In-Depth Characterization of Alpha Rhythm Modulation

The Brainwave Entrainment (BWE) hypothesis suggests that it is possible to induce neuromodulation through non-invasive auditory or visual stimulation, enhancing cortical activity at the stimulation frequency. Many studies have investigated the BWE effect of binaural beats (BB), applying stimulation within EEG frequency bands to modulate cognitive functions or elicit specific mental states. However, evidence on the effectiveness of BB in altering brain activity remains inconsistent. The present study introduces a protocol to evaluate both short- and long-term effects of BB stimulation. The primary aim is to determine whether brain activity during and after BB exposure differs from resting conditions, and to explore changes within the frequency band targeted by stimulation. The study involved 11 university students (7 males and 4 females, mean age 24.8 ± 1.6 years) over a two-week period including three acquisition checkpoints, each lasting 20 minutes. Each session was divided into three phases (Baseline, Stimulation, Post Stimulation) during which EEG and EG signals were recorded for each participant. During the first session, a personalized audio track was created for each participant, and their initial response to the BB was recorded. Over the following 10 days, subjects listened to the track daily for 10 minutes. The second session was conducted at the end of this training period. Between the second and third checkpoints, home stimulation was discontinued. The audio track featured BB created with a carrier tone (f0) of 250 Hz and a personalized stimulation frequency (&#948;f), adapted to each subject’s Individual Alpha Frequency (IAF). The EEG signals were analyzed using a multivariate approach combining Principal Component Analysis (PCA) and k-means clustering. Additionally, the alpha rhythm was examined through morphological characterization of alpha spindles and Detrended Fluctuation Analysis (DFA) of the signal envelope. Clustering on PCA-transformed data showed an average accuracy over 81.68% in distinguishing Stimulation from Baseline, and over 89.90% between Baseline and Post-Stimulation, across all acquisition sessions. An extended analysis aggregating all sessions yielded 74.40% accuracy for Stimulation and 85.09% for Post-Stimulation. Statistical significance was validated through non-parametric permutation testing. Alpha rhythm analysis revealed significant changes (at least p < 0.05) in the frontal region, particularly at F3 and F4. These included an increased incidence rate and a decreased average duration of alpha spindles, along with reduced alpha band power. Additionally, the DFA-derived &#945; exponent significantly decreased across most channels during and after stimulation. The results suggest that BB are capable of modulating brain activity, enabling a clear distinction between the stimulation and post stimulation phases compared to rest. The greater separation observed after stimulation suggests that during listening, the effects of stimulation confirm the ability of BB to modulate brain rhythms at the stimulation frequency, especially in the frontal region. Furthermore, the lack of statistically significant differences between stimulation and post stimulation phases suggests a prolonged entrainment effect.