Changes in high-frequency aperiodic 1/f slope and periodic activity reflect post-stimulus functional inhibition in the visual cortex.

It has been shown that cessation of intensive sensory stimulation is associated with a transient increase in functional inhibition in the sensory cortical areas. However, the electrophysiological correlates of this post-stimulus inhibition in the human brain have not been thoroughly investigated. To investigate post-stimulus inhibition, we analyzed magnetoencephalogram (MEG) recorded at rest and after cessation of visual stimulation of varying intensity (high-contrast gratings drifting at a slow, medium, or high rate) in 25 healthy women aged 18-40 years. We analyzed condition- and intensity-related changes in MEG parameters sensitive to functional inhibition: periodic alpha-beta power, peak alpha frequency (PAF), and 1/f aperiodic slope. We also investigated the association of these parameters with sensory sensitivity and avoidance assessed by a questionnaire. To evaluate the influence of hormonal status on the studied parameters, participants were examined twice, during the follicular and luteal phases of the menstrual cycle (MC). Regardless of the MC phase, increasing drift rate of visual gratings resulted in a proportional increase of post-stimulus posterior alpha-beta power, PAF, and a negative shift of the aperiodic (1/f) slope of the power spectrum in the high-frequency range. Compared to rest, the post-stimulus periods were characterized by higher PAF, more negative 1/f slope in posterior cortical areas, and a widespread increase in beta power. While condition- and drift-rate-dependent modulations of alpha-beta power and 1/f slope were correlated, changes in PAF did not correlate with either of them. A greater intensity-dependent increase in visual alpha-beta power predicted higher subjective sensory sensitivity/avoidance, suggesting stronger regulatory top-down modulation of the visual cortex in individuals with heightened sensitivity. Our results show that several MEG parameters concordantly indicate a post-stimulus enhancement of inhibition that is proportional to the intensity of the preceding visual stimulation. While post-stimulus changes in alpha-beta power and 1/f slope may share some common mechanisms, changes in PAF reflect a distinct aspect of inhibitory regulation. Our results inform potential inhibition-based biomarkers for clinical and translational research.