Random Tactile Noise Stimulation Reveals Beta-Rhythmic Impulse Response Function of the Somatosensory System

Both passive tactile stimulation and motor actions result in dynamic changes in beta-band (15-30 Hz Hz) oscillations over somatosensory cortex. Similar to alpha-band (8-12 Hz) power decrease in the visual system, beta-band power also decreases following stimulation of the somatosensory system. This relative suppression of alpha and beta oscillations is generally interpreted as an increase in cortical excitability. Here, next to traditional single-pulse stimuli, we employed a random intensity continuous right index finger tactile stimulation (white noise), which enabled us to uncover an impulse response function (IRF) of the somatosensory system. Contrary to previous findings, we demonstrate a burst-like initial increase rather than decrease of beta activity following white noise stimulation (human participants, N = 18, 8 female). These beta bursts, on average, lasted for 3 cycles and their frequency was correlated with resonant frequency of somatosensory cortex, as measured by a multi-frequency steady-state somatosensory evoked potential (SSSEP) paradigm. Furthermore, beta-band bursts shared spectro-temporal characteristics with evoked and resting-state beta oscillations. Taken together, our findings not only reveal a novel oscillatory signature of somatosensory processing that mimics the previously reported visual IRFs, but also point to a common oscillatory generator underlying spontaneous beta bursts in the absence of tactile stimulation and phase-locked beta bursts following stimulation, the frequency of which is determined by the resonance properties of the somatosensory system. Significance Statement The investigation of transient nature of oscillations has gained great popularity in recent years. The findings of bursting activity rather than sustained oscillations in beta-band has provided important insights into its role in movement planning, working memory, inhibition and reactivation of neural ensembles. In this study, we show that also in response to tactile stimulation somatosensory system responds with ~3 cycle oscillatory beta-band bursts, spectro-temporal characteristics of which are shared with evoked and resting-state beta-band oscillatory signatures of the somatosensory system.