Broadband neural oscillatory dynamics at stimulus onset and offset during 40-Hz auditory stimulation

The 40-Hz auditory steady-state response (ASSR) has been examined extensively because of its association with gamma-band oscillations and its potential as a biomarker for psychiatric disorders. However, most studies have focused particularly on neural activity at the driving frequency, with less focus on the temporal evolution of oscillations across other frequency bands during auditory stimulation. We aimed to elucidate the broadband oscillatory dynamics during 40-Hz click trains, focusing on stimulus onset and offset. Magnetoencephalography recordings were obtained from 30 healthy adults exposed to 40-Hz auditory stimuli. The auditory cortex sources were reconstructed using a bilateral two‑dipole model, and the amplitude and intertrial phase coherence (ITPC) in the 4-100-Hz range were quantified through time‑frequency analysis. Both stimulus onset and offset exhibited transient increases in amplitude and ITPC spanning the theta to gamma bands. The onset and offset responses exhibited similar temporal and spectral profiles, suggesting shared neural mechanisms. These findings highlight the advantage of extending the conventional ASSR paradigm to include broadband oscillatory dynamics at both the onset and offset. This integrated approach enables simultaneous assessment of transient and steady-state responses, providing a comprehensive framework for investigating sensory processing and change detection mechanisms in both healthy individuals and clinical populations.