Effects of Theta Burst Stimulation on Suprahyoid Motor Cortex Excitability in Healthy Subjects

Continuous theta burst stimulation (cTBS) and intermittent TBS (iTBS) are powerful patterns of repetitive transcranial magnetic stimulation (rTMS), with substantial potential for motor function rehabilitation post-stroke. However, TBS of suprahyoid motor cortex excitability has not been investigated. This study investigated TBS effects on suprahyoid motor cortex excitability and its potential mechanisms in healthy subjects.

Thirty-five healthy subjects (23 females; mean age = 21.66 ± 1.66 years) completed three TBS protocols on separate days, separated by at least one week. A stereotaxic neuronavigation system facilitated accurate TMS positioning. Left and right suprahyoid motor evoked potentials (SMEP) were recorded using single-pulse TMS from the contralateral suprahyoid motor cortex before stimulation (baseline) and 0, 15, and 30 min after stimulation. The SMEP latency and amplitude were analyzed via repeated measures analysis of variance.

cTBS suppressed ipsilateral suprahyoid motor cortex excitability and activated the contralateral suprahyoid motor cortex. iTBS facilitated ipsilateral suprahyoid motor cortex excitability; however, it did not affect the contralateral excitability. iTBS eliminated the inhibitory effect caused by cTBS applied to the contralateral suprahyoid motor cortex. TBS had no significant effect on the latencies of bilateral SMEP. TBS effects on suprahyoid motor cortex excitability lasted a minimum of 30 min.

TBS effectively regulates suprahyoid motor cortex excitability. Suppression of excitability in one hemisphere leads to further activation of the corresponding contralateral motor cortex. iTBS reverses the inhibitory effect induced by cTBS of the contralateral suprahyoid motor cortex.