Assessing neuromodulation effects of theta burst stimulation to the
prefrontal cortex using TMS-EEG
Abstract
Theta burst stimulation (TBS), a form of repetitive transcranial
magnetic stimulation (TMS), is capable of non-invasively modulating
cortical excitability. TBS is gaining popularity as a therapeutic tool
for psychiatric disorders such as depression, in which the dorsolateral
prefrontal cortex (DLPFC) is the main therapeutic target. However, the
neuromodulatory effects of TBS on prefrontal regions remain unclear.
Concurrent transcranial magnetic stimulation and electroencephalography
(TMS-EEG) can assess neuromodulation in non-motor regions using
TMS-evoked potentials (TEPs) and event-related
synchronisation/desynchronisation (ERS/D). We assessed twenty-four
healthy participants (13 males, mean age 25.2±9.9 years) in a
single-blinded crossover study design, following intermittent TBS,
continuous TBS, and sham applied to the left DLPFC. TEPs and ERS/ERD
were obtained at baseline and 2-, 15-, and 30-min post-stimulation. Four
TEP components (N40, P60, N100 and P200) and two frequency bands (theta
and gamma) were analysed using mixed effects repeated measures models
(MRMM). Results indicated no significant effects for any assessed
components or frequency bands. Relative to sham, the largest TEP effect
size was obtained for the N100 component at 15 minutes post-iTBS (d =
-0.50), and the largest frequency effect was obtained for gamma ERS at
15 minutes post-cTBS (d = 0.53). These results were in the same
direction but smaller than found in previous studies, suggesting that
effect sizes of the neuromodulatory effects of TBS may be lower than
previously reported.