Quantitative assessment of pain threshold induced by a single-pulse transcranial magnetic stimulation

Objective Transcranial magnetic stimulation (TMS) is commonly used in basic research to evaluate human brain function. Although scalp pain is a side effect, no studies have quantitatively assessed the TMS intensity threshold for inducing pain and whether sensitivity to TMS-induced pain differs between sexes. Methods We measured pain thresholds when single-pulse TMS was applied over either Broca’s area (BA) or left primary motor cortex (M1). We compared these thresholds with motor threshold for inducing motor evoked potential (MEP) through M1 stimulation. We also compared pain thresholds for BA and M1 between males and females. Results Pain thresholds for both sites were significantly lower than motor threshold. Further, the pain threshold for BA was much lower than that for M1. No significant difference was observed between sexes. Conclusion The results suggest that TMS at an intensity equivalent to motor thresholds, which is often used in experimental or clinical studies, causes slight scalp pain. Significance Experimental designs using TMS to evaluate functional relationships between brain and behaviors should consider scalp pain and reduce its likelihood as much as possible. Highlights We investigated pain thresholds induced by a single-pulse TMS over the head. Pain thresholds for TMS over Broca’s area (BA) and primary motor cortex (M1) were much lower than motor threshold. No significant differences in the pain thresholds were observed between sexes.