Differential neural responses to rhythmic and patterned TMS protocols: Insights from EEG spectral analysis

Area of Science:

• Neuroscience
• Psychiatry
• Biomedical Engineering

Background:

• Repetitive Transcranial Magnetic Stimulation (rTMS) is a neuromodulation technique used for treating Major Depressive Disorder (MDD).
• rTMS employs various protocols, including rhythmic and patterned stimulation (e.g., intermittent Theta Burst Stimulation - iTBS).
• The differential effects of these rTMS protocols on brain function remain incompletely understood.

Purpose of the Study:

• To investigate the distinct effects of rhythmic and patterned rTMS protocols on brain oscillatory activity and effective connectivity.
• To examine how stimulation frequency influences these neural changes within the left dorsolateral prefrontal cortex (L-DLPFC).

Main Methods:

• Sixteen MDD subjects underwent a TMS-electroencephalography (TMS-EEG) paradigm.
• A wide range of rhythmic and patterned stimulation frequencies were applied to the L-DLPFC in a randomized order.
• Linear mixed-effects models were used to analyze changes in power, connectivity, and source localization.

Main Results:

• Both rhythmic and patterned rTMS induced widespread changes in brain power and connectivity, dependent on protocol and frequency.
• Patterned stimulation predominantly increased beta band power, while rhythmic stimulation increased alpha and beta power above 7 Hz.
• Distinct regional activations (cingulate) and connectivity patterns (precuneus, orbitofrontal cortex) were observed for each protocol.

Conclusions:

• Rhythmic and patterned rTMS protocols engage distinct brain networks in a frequency- and protocol-specific manner.
• These findings highlight the mechanistic differences between rTMS protocols.
• Further research is needed to correlate these neural distinctions with clinical outcomes in MDD treatment.