Effect of electrode cap on measured cortical motor threshold

Area of Science:

• Neuroscience
• Motor Control
• Transcranial Magnetic Stimulation (TMS)

Background:

• The cortical motor threshold (MT) is a key parameter in transcranial magnetic stimulation (TMS) research.
• Standardized protocols are crucial for reliable and comparable MT measurements.
• The use of electrode caps in TMS procedures may influence MT determination.

Purpose of the Study:

• To investigate the impact of electrode cap use on cortical motor threshold (MT) determination.
• To assess the effectiveness of a mathematical correction method in mitigating electrode cap-induced changes in MT.
• To evaluate the effect of electrode caps on motor evoked potentials (MEPs).

Main Methods:

• Sixteen healthy subjects participated in the study.
• Navigated transcranial magnetic stimulation (TMS) was employed to map the thenar musculature's primary motor cortex representation.
• Individual MTs were determined with and without an electrode cap, followed by application of a mathematical correction method.

Main Results:

• A significant increase in determined MTs was observed when using an electrode cap (p<0.05).
• The mathematical correction method significantly reduced the MT difference at the group level (p<0.01) but was poorly effective at the individual level.
• MEP amplitudes remained unaffected by the presence or absence of the electrode cap.

Conclusions:

• Electrode cap use significantly alters cortical MT measurements, complicating comparisons across studies.
• While a correction method shows promise at a group level, its individual efficacy is limited.
• Standardization of TMS protocols, considering electrode cap usage, is essential for reproducible research.