Differential modulation of sensorimotor beta oscillations by beta tACS alone and combined repetitive paired-pulse TMS with tACS

• We tested the effects of repetitive paired-pulse TMS (rPPS), tACS, and their combination on beta activity. • rPPS-tACS increased cortico-muscular coherence and PMBR within the high beta range. • tACS alone enhanced resting beta power and low-beta PMBR. • rPPS alone did not modulate beta oscillations in the sensorimotor cortex. • rPPS-tACS and tACS alone may affect different sensorimotor beta networks. Combined stimulation with transcranial alternating current stimulation (tACS) at the beta frequency and repetitive paired-pulse transcranial magnetic stimulation (rPPS) produces different after-effects on cortical excitability in the primary motor cortex (M1) compared with either stimulation alone. Sensorimotor beta oscillations are broadly implicated in resting-state activity, as well as in phasic and sustained movements. However, whether combined stimulation can modulate oscillatory activities remains unclear. To address the effects of combined stimulation on sensorimotor beta oscillations. We applied rPPS pulses synchronized with the peak phase of beta tACS (rPPS-tACS), rPPS with sham tACS (rPPS alone), or tACS without rPPS (tACS alone). Cortico-muscular coherence (CMC), movement-related beta desynchronization (MRBD), post-movement beta rebound (PMBR), and beta power during the resting-state and CMC tasks were measured before and after the intervention to assess their impact on sensorimotor beta oscillations. rPPS-tACS increased the CMC and decreased the aperiodic offset. A strong correlation was observed between CMC modulation and beta burst rate in the rPPS-tACS condition. tACS alone increased resting beta power, whereas rPPS alone did not modulate any measurements. Moreover, although rPPS-tACS and tACS alone increased the PMBR, their after-effects emerged at high- and low-beta oscillations, respectively. Our results suggest that rPPS-tACS and tACS alone over M1 may modulate distinct neural populations underlying sensorimotor beta oscillations. Our combined stimulation with rPPS and beta tACS may be a useful approach for elucidating the diverse functional roles of these oscillations.