The After-Effect of Accelerated Intermittent Theta Burst Stimulation at Different Session Intervals

Objective The study aims to investigate the after-effect of three sessions of intermittent theta-burst stimulation (iTBS) on motor cortical excitability. The iTBS was induced over the primary motor cortex (M1) at different time intervals. Methods The study has a crossover design. Sixteen participants were assigned to three groups and received different accelerated iTBS (aiTBS) protocols during each visit: (1) three continuous sessions with no interval (iTBS18000); (2) three iTBS sessions with 10-min intervals (iTBS600 x 3*10); and (3) three iTBS sessions with 30-min intervals (iTBS600 x 3*30). As washout period, each visit is separated by at least 7 days. We measured the motor cortical excitability changes and intracortical inhibition. Results A dose of 1,800 pulses of aiTBS per day is tolerable. The iTBS1800 led to a reduced cortical excitability; whereas iTBS600 x 3*10 and iTBS600 x 3*30 enhanced cortical excitability to a differential extent. After a total dose of 1,800 pulses, iTBS600 x 3*30 exhibited the longer effect and highest percentage of individuals with enhanced cortical excitability. Conclusion The results suggest that aiTBS protocols at different time intervals result in different motor cortical excitability after-effects.