Optimizing plasticity: the impact of time intervals between priming cTBS and subsequent iTBS on motor-evoked...

This study investigated how varying time intervals between priming continuous theta burst stimulation (cTBS) and intermittent theta burst stimulation (iTBS) affect motor cortex plasticity in healthy adults. Using a randomized crossover design, 31 participants underwent four cTBS-iTBS protocols with intervals of 0, 5, 10, or 15 min, with motor-evoked potential (MEP) amplitudes measured at baseline and post-intervention. The results revealed significant main effects of both the stimulation condition and time point on normalized MEP amplitudes. Among the four protocols, the cTBS-10 min-iTBS protocol elicited the greatest facilitatory effect, producing significantly greater MEP enhancement than the 0-, 5-, and 15-minute intervals. The normalized MEP amplitudes showed a time-dependent decline, with the highest values observed at 0 min and the lowest at 30 min post-intervention. These findings suggest that the time intervals between cTBS and iTBS may influence the resulting facilitation effects, offering preliminary evidence that may inform future optimization of TBS-based therapeutic applications.