Intermittent theta burst stimulation over primary motor cortex enhances movement-related beta synchronisation

ObjectiveThe objective of this study is to investigate how transcranial magnetic intermittent theta burst stimulation (iTBS) with a prolonged protocol affects human cortical excitability and movement-related oscillations.MethodsUsing motor-evoked potentials (MEPs) and movement-related magnetoencephalography (MEG), we assessed the changes of corticospinal excitability and cortical oscillations after iTBS with double the conventional stimulation time (1200 pulses, iTBS1200) over the primary motor cortex (M1) in 10 healthy subjects. Continuous TBS (cTBS1200) and sham stimulation served as controls.ResultsiTBS1200 facilitated MEPs evoked from the conditioned M1, while inhibiting MEPs from the contralateral M1 for 30 min. By contrast, cTBS1200 inhibited MEPs from the conditioned M1. Importantly, empirical mode decomposition-based MEG analysis showed that the amplitude of post-movement beta synchronisation (16–26 Hz) was significantly increased by iTBS1200 at the conditioned M1, but was suppressed at the nonconditioned M1. Alpha (8–13 Hz) and low gamma-ranged (35–45 Hz) rhythms were not notably affected. Movement kinetics remained consistent throughout.ConclusionsTBS1200 modulated corticospinal excitability in parallel with the direction of conventional paradigms with modestly prolonged efficacy. Moreover, iTBS1200 increased post-movement beta synchronisation of the stimulated M1, and decreased that of the contralateral M1, probably through interhemispheric interaction.SignificanceOur results provide insight into the underlying mechanism of TBS and reinforce the connection between movement-related beta synchronisation and corticospinal output.

► Theta burst stimulation with doubled number of stimuli (TBS1200) modulates motor cortical excitability in parallel with the conventional protocols, with modestly prolonged efficacy.
► Facilitatory intermittent theta burst stimulation (iTBS1200) alters motor task-dependent beta frequency oscillation.
► Prolonged theta burst stimulation (TBS1200) may be suited to enhance the stability of its effect on motor cortical excitability.