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-modulated) yields a more pronounced narrowband response centered at 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. This study evaluates EEG-level detectability of 40 Hz–centered neural signatures and does not assess cognitive/clinical efficacy or therapeutic benefit. Across metrics, the 40 Hz ON soundscape showed a consistent ON > OFF directionality, including localized electrode-level signals and a temporal-region summary measure under nominal, uncorrected testing, accompanied by a clearer narrowband feature near 40 Hz in spectral profiles. Overall, the observed trends are consistent with the feasibility of embedding an additive 40 Hz layer into a naturalistic soundscape in a manner that yields EEG-quantifiable, 40 Hz centered signatures; however, because this is an exploratory pilot without multiplicity control, all effects should be interpreted as hypothesis-generating and warrant confirmation in larger, preregistered studies with multiplicity-aware inference.