Can Soundscapes Carry 40 Hz for Gamma Entrainment? : Evidence from a Pilot EEG Study

This pilot EEG study examined the feasibility of a soundscape-based 40-Hz auditory stimulation format by using a soundscape-only condition as a contrast control. We tested whether a nature-based soundscape with an additively layered pure 40-Hz sine component (40-Hz ON; not amplitude modulation) produces a more pronounced narrowband neural response around 40 Hz than the same soundscape without the 40-Hz layer (40-Hz OFF). Participants completed both conditions in a single-blind, randomized-order, within-participant crossover session with a washout interval. EEG outcomes included 40-Hz power, frequency-domain SNR around 40 Hz, scalp distribution of 40-Hz power, and phase-based connectivity in the gamma range. Across metrics, the 40-Hz ON soundscape showed a consistent ON>OFF directionality, including localized electrode-level signals and a temporal-region summary signal under nominal, uncorrected testing, accompanied by a clearer narrowband feature near 40 Hz in spectral profiles. These convergent patterns support the interpretation that embedding a 40-Hz layer into a naturalistic soundscape can engage frequency-specific gamma activity and may be a viable neuroacoustic stimulation approach. As an exploratory pilot study without multiplicity control, the findings are hypothesis-generating and motivate confirmatory studies with larger samples and preregistered endpoints.