Abstract
Theta-burst stimulation (TBS) is a form of repetitive transcranial magnetic stimulation (rTMS) developed to induce neuroplasticity. TBS usually consists of 50 Hz bursts at 5 Hz intervals. It can facilitate motor evoked potentials (MEPs) when applied intermittently, although this effect can vary between individuals. Here, we sought to determine whether a modified version of intermittent TBS (iTBS) consisting of 30 Hz bursts repeated at 6 Hz intervals would lead to lasting MEP facilitation. We also investigated whether recruitment of early and late indirect waves (I-waves) would predict individual responses to 30 Hz iTBS. Participants (n = 19) underwent single-pulse TMS to assess MEP amplitude at baseline and variations in MEP latency in response to anterior-posterior, posterior-anterior, and latero-medial stimulation. Then, 30 Hz iTBS was administered, and MEP amplitude was reassessed at 5-, 20- and 45-min. Post iTBS, most participants (13/19) exhibited MEP facilitation, with significant effects detected at 20- and 45-min. Contrary to previous evidence, recruitment of early I-waves predicted facilitation to 30 Hz iTBS. These observations suggest that 30 Hz/6 Hz iTBS is effective in inducing lasting facilitation in corticospinal excitability and may offer an alternative to the standard 50 Hz/5 Hz protocol.
Highlights
Theta Burst Stimulation (TBS) is a form of repetitive transcranial magnetic stimulation introduced in the mid-2000s by Huang et al [1]
Wu et al [14] showed that 600 pulses of intermittent TBS (iTBS) consisting of 30 Hz bursts repeated at 5 Hz intervals were effective in inducing motor evoked potentials (MEPs) facilitation up to 10 min in healthy adults, while Pedapati et al [15] made similar observations in children using the same iTBS parameters but for 300 pulses
The inverse relationship we found between AP-LM/PA latency differences and MEP modulation suggests that preferential recruitment of early indirect waves (I-waves) was likely an important factor in mediating the aftereffects of 30 Hz iTBS
Summary
Theta Burst Stimulation (TBS) is a form of repetitive transcranial magnetic stimulation (rTMS) introduced in the mid-2000s by Huang et al [1]. Huang et al [1] demonstrated that a combination of 20 cycles of 50 Hz bursts repeated every 200 ms (i.e., 5 Hz) was effective in inducing lasting modulation in corticospinal excitability, as reflected in the amplitude of motor evoked potentials (MEPs). A minority of investigators have considered modifications to the ‘standard’ to determine whether altering TBS parameters could lead to more robust aftereffects In this respect, Goldsworthy et al [10], based on observations by Nyffeler et al [11] regarding the effects of 30 Hz TBS on the oculomotor system, propose a modification to the original TBS protocol described by Huang et al [1]. In a recent systematic review of TBS effects, Chung et al [3] concluded that, there was evidence to suggest that 30 Hz TBS might produce more persistent and larger effects than 50 Hz TBS, more studies were required to validate its reliability
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