Effects of 30 Hz Theta Burst Transcranial Magnetic Stimulation on the primary motor cortex

Theta Burst Stimulation (TBS) is a relatively new form of repetitive Transcranial Magnetic Stimulation (TMS) used to probe neuroplasticity in the human cortex. Thirty-Hz TBS, a variation of the originally described 50 Hz TBS, has been shown to induce cortical changes in several nonmotor regions. However, its effects over the primary motor cortex have not been examined. Due to TMS device mechanical properties, 30 Hz TBS is advantageous over 50 Hz TBS in that it can be delivered at higher stimulation intensities. The goal of this pilot study is to examine the neurophysiologic effects of 30 Hz TBS on the primary motor cortex (M1) of healthy adults. Eighteen right-handed adults (33 +/- 9.0 years; M: F = 8:10) completed intermittent TBS (iTBS) or continuous TBS (cTBS) over left M1. TBS was performed with Magstim(R) SuperRapid2 with stimulation bursts (3 pulses at 30 Hz) repeating every 200 ms. For iTBS, each 2-s stimulation train was separated by 8s but there was no pause between trains for cTBS. Each TBS consisted of a total of 600 pulses delivered at an intensity of 90%*Resting Motor Threshold. Motor-Evoked Potentials (MEP) in the right first dorsal interosseous muscle were measured before, and one and ten minutes after TBS. Pre/post-TBS MEP amplitudes were compared using repeated-measures ANOVA. MEP amplitudes increased after 30 Hz iTBS and decreased after 30 Hz cTBS (TBS-Type*Time effect p = 0.009). In conclusion, 30 Hz TBS induced similar neurophysiologic effects over M1 as conventional 50 Hz TBS. (C) 2012 Elsevier B.V. All rights reserved.