The role of beta bursts in top-down inhibition of somatosensory cortex: an OPM-MEG study

Human brain electrophysiology is characterised by rhythmic activity – neural oscillations – which play an important role in coordinating brain function. In the somatosensory cortices, the dominant oscillations occur in the beta (13-30 Hz) band and are thought to mediate top-down inhibition of primary cortices. The non-invasive measurement of such oscillations has traditionally been made possible using either electroencephalography (EEG) or magnetoencephalography (MEG), yet both modalities have significant limitations. Here, we use a new MEG technology – based on optically pumped magnetometers (OPM-MEG) – to measure attentional modulation of beta oscillations in the somatosensory cortex. Using piezo-electric crystal stimulators, we present ‘braille-like’ patterns to the left and right index fingers; participants are asked to respond to pre-specified target patterns presented to an attended hand, whilst ignoring patterns presented to their non-attended hand. In agreement with previous findings, we measure significantly decreased beta amplitude during attended stimuli relative to baseline, and to non-attended stimuli, with the most pronounced effect during an attentional cue. Moreover, we extend our analyses to demonstrate that attention has a similar effect on the occurrence of pan-spectral bursts (which are shown to underlie the beta rhythm). Specifically, we measure significant changes in the probability of burst occurrence in primary somatosensory cortices in a time window related to attentional shifts. In sum, our results provide evidence that attentional modulation of beta oscillations is driven by changes in pan-spectral burst occurrence and add weight to the argument that OPM-MEG is the technique of choice for non-invasive electrophysiological measurements.