Assessing Neuromodulation Effects of Theta Burst Stimulation to the Prefrontal Cortex Using Transcranial Magnetic...

Area of Science:

• Neuroscience
• Psychiatry
• Neuroimaging

Background:

• Theta burst stimulation (TBS), a repetitive transcranial magnetic stimulation (TMS) technique, is increasingly used to modulate cortical excitability for psychiatric disorders.
• The dorsolateral prefrontal cortex (DLPFC) is a key target for TBS in depression, but its precise neuromodulatory effects remain unclear.
• Concurrent TMS and electroencephalography (TMS-EEG) offers a method to assess neuromodulation in non-motor regions via TMS-evoked potentials (TEPs) and event-related synchronisation/desynchronisation (ERS/D).

Purpose of the Study:

• To investigate the neuromodulatory effects of intermittent TBS (iTBS) and continuous TBS (cTBS) on the left DLPFC in healthy participants using TMS-EEG.
• To quantify changes in TEP components and theta/gamma band ERS/D at various time points post-stimulation.
• To compare the observed effect sizes with previous findings and assess the reliability of TBS neuromodulation.

Main Methods:

• A single-blinded crossover study involving 24 healthy participants.
• Application of iTBS, cTBS, and sham stimulation to the left DLPFC.
• Measurement of TEPs (N40, P60, N100, P200) and ERS/D (theta and gamma bands) at baseline and 2, 15, and 30 minutes post-stimulation.
• Analysis using mixed-effects repeated measures models (MRMM).

Main Results:

• No statistically significant effects were found for any assessed TEP components or frequency bands across stimulation conditions.
• The largest observed TEP effect size was for the N100 component at 15 minutes post-iTBS (d = -0.50).
• The largest frequency effect size was for gamma ERS at 15 minutes post-cTBS (d = 0.53).
• These effect sizes were in the same direction but smaller than those reported in prior research.

Conclusions:

• The study found limited evidence for significant neuromodulation of the left DLPFC by TBS in healthy individuals.
• Observed effect sizes for TEPs and ERS/D were smaller than expected, suggesting that the neuromodulatory impact of TBS might be lower than previously suggested.
• Further research is needed to clarify the efficacy and underlying mechanisms of TBS in clinical applications, particularly for psychiatric disorders targeting prefrontal regions.