The excitability of the sensorimotor (SM1) cortices is reflected in the bilateral ~20 Hz beta oscillations. The extent to which these oscillations subtend the interhemispheric inhibition (IHI) captured by the Transcranial Magnetic Stimulation (TMS) ipsilateral Silent Period (iSP) protocol remains unclear. Therefore, we investigated the relationship between movement-related beta suppression and the iSP, along with their role for manual dexterity. Forty adults underwent an Electroencephalography assessment of beta suppression during volitional left-hand movement and a TMS assessment of iSP recorded from the right hand. In both cases, left SM1 beta oscillations (contralateral to the activated right SM1) were monitored through a proxy signal—the Electromyography of the contracted right hand. Bimanual dexterity was assessed with the Purdue Pegboard. Volitional movement caused significant bilateral SM1 beta suppression in nearly all participants (≥85%). ISPs were observed in every participant. In the proxy signal for the left SM1, the iSP coincided with TMS-evoked high-amplitude beta bursts. These bursts showed significant phase alignment across participants 10–70 ms after the TMS pulse. There was no significant association between the left-/right-hemisphere beta suppression, iSP, and bimanual dexterity. Our results highlight the distinct nature of beta oscillation changes during volitional movement compared with TMS-iSP and show that TMS induces IHI via transcallosal generation of phase-aligned beta bursts. Furthermore, our data suggest that only the initial phase of a beta burst carries an inhibitory effect. It also highlights the possibility of evoking a beta burst with the iSP protocol, opening perspectives for future neuroimaging and modeling studies.

Characterizing the early development of the human brain is critical from both fundamental and clinical perspectives. However, existing neuroimaging techniques are either not well suited to infants or have limited spatial or temporal resolution. The advent of optically pumped magnetometers (OPMs) has revolutionized magnetoencephalography (MEG) by enabling wearable and thus more naturalistic recordings while maintaining excellent sensitivity and spatiotemporal resolution. Nevertheless, its adaptation to studying neural activity in infancy poses several challenges. In this work, we present an original close-to-scalp OPM-MEG setup that successfully recorded brain responses to sounds in newborns. We exposed 1-month-old infants to continuous streams of tones and observed significant evoked responses, which peaked ~250 ms poststimulus at bilateral auditory cortices. When tones were presented at a steady fixed pace with an oddball tone every fourth tone, significant neural responses were found both at the frequency of the standard tones (3 Hz) and of the oddball tones (0.75 Hz). The latter reflects the ability of the newborn brain to detect auditory change and synchronize to regular auditory patterns. Additional analyses support the added value of triaxial OPMs to increase the number of channels on small heads. Finally, OPM-MEG responses were validated with those obtained from the same participants using an adult-sized cryogenic MEG. This study demonstrates the applicability of OPM-MEG to study early postnatal periods; a crucial step towards future OPM investigations of typical and pathological early brain development.