Waveform matters: enhanced cortical plasticity with monophasic intermittent theta-burst stimulation

Area of Science:

• Neuroscience
• Neuromodulation
• Cognitive Science

Background:

• Activity-dependent plasticity, including long-term potentiation (LTP), is crucial for learning and memory.
• Intermittent theta-burst stimulation (iTBS), a form of repetitive transcranial magnetic stimulation (rTMS), can induce LTP-like effects.
• Conventional iTBS uses biphasic pulses, but monophasic pulses may offer enhanced cortical excitability effects.

Purpose of the Study:

• To investigate the comparative effects of monophasic versus biphasic iTBS on corticospinal excitability.
• To test the hypothesis that monophasic iTBS produces greater facilitation of motor evoked potentials (MEPs) than biphasic iTBS.

Main Methods:

• A double-blinded, placebo-controlled, within-subjects study involving 40 participants.
• Participants received monophasic, biphasic, and sham iTBS in a pseudo-randomized order.
• Transcranial magnetic stimulation (TMS) measures, including MEPs, ICF, and SICI, were recorded pre- and post-stimulation.

Main Results:

• No significant sex differences were observed in response to iTBS.
• Monophasic iTBS significantly increased MEP amplitude, while biphasic iTBS showed no significant effect.
• Intracortical facilitation (ICF) and short-interval intracortical inhibition (SICI) remained unchanged by either stimulation type.

Conclusions:

• Monophasic iTBS effectively enhances corticospinal excitability.
• These results suggest monophasic iTBS may be a more effective protocol for neuromodulatory interventions and brain stimulation therapies.