Transient cortical activity modulates somatosensory gating during postural control

Human somatosensory responses vary with movement-related gating as well as with fluctuations in ongoing cortical activity. During standing, both somatosensory responses and cortical activity change in response to postural demands. However, little is known regarding whether moment-to-moment fluctuations in cortical activity contribute to variation in somatosensory responses during different postural tasks. In this study, we investigated whether somatosensory-evoked potentials (SEPs) during postural control are associated with prestimulus cortical activity, focusing on oscillatory amplitudes and corticocortical connectivity. SEPs evoked by tibial nerve stimulation were recorded in 18 healthy adults under four postural conditions. Canonical correlation analysis (CCA) was used to extract single-trial SEP amplitudes from multichannel electroencephalography (EEG). The results showed that the early component of CCA-SEPs, N80, was significantly reduced according to postural demands. A higher prestimulus amplitude in the β-frequency band in the central cortical regions was associated with a larger N80 amplitude. Moreover, modulation of α-band corticocortical connectivity involving frontal and parietal regions covaried with N80 reduction. Clustering analysis using β-amplitude and α-connectivity as features further indicated that multivariate prestimulus cortical activity accounted for variability in N80 amplitude. These findings revealed that somatosensory responses vary through posture-related somatosensory gating and as a function of ongoing fluctuations in cortical activity. Clarifying the temporal dynamics of somatosensory processing will help elucidate the underlying physiological mechanisms of standing balance and contribute to the development of novel physiological assessments of postural impairments.