40 Hz Audiovisual Stimulation Improves Sustained Attention and Related Brain Oscillations

Attokaren, Matthew K.; Zhang, Lu; Mettupalli, Sindhura; Singer, Annabelle C. · 2025 · Crossref

DOI: 10.1101/2025.08.25.671937

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Summary

This study investigates whether acute, non-invasive 40 Hz audiovisual stimulation improves sustained attention and modulates associated neural oscillations in healthy adults. While 40 Hz "flicker" has shown promise in reducing Alzheimer’s pathology in animal models, its acute cognitive effects in humans remain unclear. Specifically, it is unknown whether exogenously driven gamma oscillations enhance or disrupt endogenous neural processes underlying attention. The authors hypothesized that 40 Hz sensory stimulation would improve performance on an attentional vigilance task and alter brain activity patterns linked to arousal and attention. The researchers conducted a randomized controlled trial with 62 healthy adults (ages 18–40) divided into three groups: 40 Hz flicker, random flicker (sham), and constant light (control). Participants underwent one hour of stimulation while performing a psychomotor vigilance task (PVT), requiring them to detect unpredictable color changes on a screen. Scalp EEG was recorded using a 32-channel system to measure neural oscillations and functional connectivity. The 40 Hz group received flashing lights and sounds at 40 Hz, while control groups received stimuli matched for average intensity but lacking periodicity. Data were analyzed for behavioral performance, power spectral density across frequency bands (delta, theta, alpha, beta, gamma), and functional connectivity using weighted phase lag index. Results demonstrated that participants exposed to 40 Hz flicker exhibited significantly better vigilance performance than those in control groups, characterized by higher accuracy (98.4% vs. ~94.5–94.7%) and faster reaction times (approximately 10–11% faster). Neurophysiologically, the 40 Hz group showed the expected increase in gamma-band power at the stimulation frequency. Surprisingly, they also exhibited significantly reduced delta power (2–4 Hz), a frequency associated with drowsiness and reduced arousal. Furthermore, the 40 Hz group displayed increased functional connectivity in the lower alpha band (8–10 Hz). Crucially, across all participants, lower delta power and higher lower alpha functional connectivity were significantly correlated with improved task accuracy and faster reaction times. These findings indicate that acute 40 Hz audiovisual stimulation enhances sustained attention in healthy adults, likely by suppressing delta oscillations associated with fatigue and enhancing alpha-band connectivity linked to attentional processing. The study reveals that the effects of gamma flicker extend beyond the gamma frequency range, engaging broader neural networks involved in arousal and cognition. This suggests potential therapeutic applications for attention disorders and cognitive enhancement, highlighting a mechanism by which sensory entrainment can modulate endogenous brain states to improve cognitive performance.

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• neuro workload indices