Pre-stimulus alpha modulates somatosensory evoked potentials during inattentive processing through localized,...

Alpha-band oscillations (8-12 Hz) are a ubiquitous feature of brain activity that profoundly shape neural processing in various domains. The functional role of these oscillations across cortical systems and brain states remains debated. Here, we investigated how pre-stimulus somatosensory alpha shapes somatosensory processing during task-irrelevant tactile stimulation. Thirty-nine participants received electrical finger stimulation while engaged in an unrelated auditory task, and high-density EEG data were recorded. The resulting somatosensory-evoked potentials (SEPs) were stratified into five bins based on pre-stimulus somatosensory alpha power and analyzed using linear mixed-effects modeling and threshold-free cluster-enhanced spatiotemporal analyses. Our results indicate that SEP amplitudes depend on pre-stimulus somatosensory alpha power. The observed effects were spatially localized to contralateral posterocentral and posteroparietal electrodes and temporally extended across multiple SEP components. Pre-stimulus alpha power was non-linearly related to SEP components, with the N250 SEP component showing an inverse U-shaped association, while P200 linearly increased with pre-stimulus alpha band power and other components showed trend-level non-linear associations. These findings provide evidence that alpha oscillations modulate task-irrelevant somatosensory processing in a component-specific and partly non-linear manner, suggesting that spontaneous local oscillatory states contribute to automatic gating of somatosensory processing, independent of task-directed attention.