Neural Dynamics of Audiovisual Entrainment: Comparative Effects of Cross-Lateralized and Bilateral Synchronous Stimulation on EEG Power and Multiscale Entropy

Audiovisual Entrainment (AVE) is an emerging non-invasive neuromodulation technique that uses rhythmic auditory and visual stimuli to modulate brain activity. This study investigates the neural effects of AVE through Electroencephalography (EEG) by comparing two distinct stimulation protocols: Cross-Lateralized Stimulation (CLS) and Bilateral Synchronous Stimulation (BSS). These methods were designed to probe the neural impact of specific AVE presentation modes across a spectrum of frequencies, including delta (2 Hz), theta (6 Hz), alpha (10 Hz), beta (16 Hz and 25 Hz), and gamma (40 Hz). A total of 26 healthy participants (12 males, 14 females; age M = 27.5, SD = 4.5) were enrolled in this within-subject study, where they underwent both AVE protocols in random sequences. EEG signals were recorded and analyzed using power spectral density (PSD) for time-frequency examination and multiscale entropy (MSE) for assessing the nonlinear complexity of brain signals. Time-frequency analysis revealed frequency-specific modulations in neural oscillations, with both CLS and BSS significantly affecting beta and gamma bands, although CLS demonstrated a broader spatial impact. In multiscale entropy analyses, instead, BSS exhibited localized entropy reductions, particularly in posterior regions and at finer temporal scales, while CLS consistently affected medium and coarse scales, impacting both central and lateral regions. These results underscore that the effects of AVE are highly dependent on both the frequency of stimulation and the presentation protocol, with CLS showing a tendency to produce more extensive neural modulation compared to the spatially constrained impact observed in BSS. The study concludes that AVE offers distinct and protocol-specific modulation of brain dynamics, with potential applications for clinical neuromodulation. However, protocol optimization remains essential, as participant fatigue was noted, particularly due to extended session durations. Future research should aim to streamline AVE parameters to enhance therapeutic efficacy and participant comfort. Overall, the findings support AVE's adaptability and efficacy as a non-invasive brain modulation method with applications for cognitive and therapeutic use, emphasizing the need for further exploration to determine optimal stimulation settings across individual and clinical variations.

Questa ricerca esplora l'impatto dell'entrainment audiovisivo (AVE) sulle attività delle onde cerebrali, utilizzando l'elettroencefalografia (EEG) per analizzare cambiamenti nella distribuzione spettrale e nella complessità dei segnali cerebrali. Lo studio confronta due modalità di presentazione di AVE: la Stimolazione Cross-Lateralizzata (CLS), che implica variazioni laterali in frequenza e presentazione uditiva, e la Stimolazione Sincrona Bilaterale (BSS), una modalità tradizionale che coinvolge entrambi i campi visivi e canali uditivi. I partecipanti sono stati suddivisi in due gruppi che hanno ricevuto una di queste due applicazioni a frequenze diverse (2, 6, 10, 16, 25 e 40 Hz) per monitorare le risposte specifiche delle bande di frequenza e le variazioni post-stimolazione. I risultati indicano che entrambe le modalità di AVE producono effetti significativi nella modulazione delle onde cerebrali, con riduzioni di entropia misurate a livelli specifici di frequenza e ampiezza. CLS ha mostrato un impatto più ampio e distribuito nel cervello a frequenze inferiori, mentre BSS ha evidenziato effetti più localizzati nelle bande beta e gamma. L'analisi evidenzia che AVE potrebbe essere efficace come tecnica di neuromodulazione non invasiva e offre un ampio potenziale terapeutico per migliorare la funzione cognitiva e gestire disturbi neurologici specifici.