Aperiodic spectral organization reveals regional differentiation during action execution and observation

Traditional frequency-domain analysis of electroencephalography (EEG) cannot readily distinguish periodic oscillations from the aperiodic spectral background, limiting the characterization of neural dynamics during visuomotor processing. Here, we investigated how motor state and visual feedback synchrony shape periodic and aperiodic spectral components across electrode-defined visual, motor, and somatosensory regions. Twenty healthy adults performed a 2×2 factorial task combining motor execution and observation with synchronous or asynchronous visual feedback. EEG spectra were parameterized using the FOOOF algorithm to separately quantify aperiodic offset and exponent and periodic spectral characteristics. The aperiodic exponent remained comparatively stable across experimental conditions, whereas aperiodic offset exhibited a strong regional effect and a significant condition-by-region interaction ( p <0.05). Pairwise analyses localized the condition-dependent modulation primarily to visual-region, where offset was lower during execution than observation under both synchronous and asynchronous feedback. No reliable synchrony-dependent difference was observed within the same motor state. These findings reveal a dissociation between a relatively stable spectral slope and a regionally organized, motor-state-dependent broadband spectral level. Parameterizing periodic and aperiodic components may therefore provide a more informative characterization of cortical spectral organization during visuomotor processing than conventional power-spectrum analysis alone.