Reliability of the TMS-evoked potential in dorsolateral prefrontal cortex

Area of Science:

• Neuroscience
• Neurophysiology
• Brain Stimulation Techniques

Background:

• Noninvasive methods to assess human dorsolateral prefrontal cortex (dlPFC) cortical excitability are limited.
• Previous research indicated variability in early and local TMS-evoked potentials (EL-TEPs) across dlPFC subregions.
• The reliability of these EL-TEPs at specific dlPFC targets remained undetermined.

Purpose of the Study:

• To quantify the within-session reliability of dlPFC EL-TEPs following TMS.
• To evaluate how different targets, analytical parameters, and trial numbers influence reliability.
• To identify optimal conditions for reliable EL-TEP measurement in the dlPFC.

Main Methods:

• Assessed within-session reliability of dlPFC EL-TEPs using the concordance correlation coefficient (CCC) in 15 healthy subjects.
• Investigated TMS to six left dlPFC subregions.
• Evaluated reliability across various targets, time windows, quantification methods, regions of interest, sensor- vs. source-space, and trial counts.

Main Results:

• The medial dlPFC target demonstrated the highest average reliability (CCC = 0.78), while the most anterior target showed the lowest (CCC = 0.24).
• Most targets (excluding the most anterior) achieved reliable EL-TEPs (CCC > 0.7) with specific analytical parameter combinations.
• Longer (20-60 ms) and later (30-60 ms) time windows, along with peak-to-peak quantification, enhanced reliability.
• Reliable EL-TEPs (CCC up to 0.86) were obtained with as few as 25 TMS trials at a medial dlPFC target.

Conclusions:

• Medial dlPFC targeting, wider time windows, and peak-to-peak quantification are key to improving EL-TEP reliability.
• Highly reliable EL-TEPs can be extracted from the dlPFC with a limited number of trials by optimizing target selection and analytical methods.
• This study provides a pathway for reliable noninvasive assessment of dlPFC cortical excitability.