Correlation between motor and phosphene thresholds: a transcranial magnetic stimulation study.

Area of Science:

• Neuroscience
• Cognitive Science
• Neuromodulation

Background:

• Transcranial magnetic stimulation (TMS) is vital for brain mapping cognitive functions.
• Calibrating TMS intensity for non-motor cortical regions is difficult due to subtle effects.
• Previous studies showed no correlation between motor and phosphene thresholds, likely due to varied methodologies.

Purpose of the Study:

• To investigate the correlation between resting motor threshold (rMT), active motor threshold (aMT), and phosphene threshold (PT).
• To determine if aMT can be used to calibrate TMS intensity for non-motor brain mapping.

Main Methods:

• Twenty-seven healthy volunteers participated.
• Resting MT, active MT, and PT were measured under standardized, dark-adapted, eyes-open conditions.
• Thresholds were determined by gradually decreasing stimulation intensity.

Main Results:

• A significant positive correlation was observed between active motor threshold (aMT) and phosphene threshold (PT) (r = 0.53, P = 0.014).
• A trend towards correlation was found between resting motor threshold (rMT) and PT (r = 0.43, P = 0.052).
• Active motor threshold (aMT) was 61.1% ± 7.9%, resting motor threshold (rMT) was 70.4% ± 9.8%, and phosphene threshold (PT) was 82.2% ± 10.1% of maximum stimulator output.

Conclusions:

• Cortical sensitivity to TMS in visual and motor areas may be correlated when using consistent thresholding methods.
• Active motor threshold (aMT) provides a reliable method for calibrating TMS intensity in non-motor brain mapping studies.