Abstract
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. In the present study, we measured pain thresholds when single-pulse TMS was applied over either Broca’s area (BA) or left primary motor cortex (M1), and compared these thresholds with the motor threshold (MT) for inducing motor evoked potentials (MEPs) through M1 stimulation. Additionally, we compared the pain thresholds for BA and M1 between males and females. We found that pain thresholds for both sites were significantly lower than the MT. Furthermore, the pain threshold for BA was much lower than that for M1. No significant difference was observed between sexes. The results suggest that TMS at an intensity equivalent to MTs, which is often used in experimental or clinical studies, causes slight scalp pain. Experimental designs using TMS to evaluate functional relationships between brain and behavior should consider scalp pain and reduce its likelihood as much as possible.
Highlights
Transcranial magnetic stimulation (TMS) is widely used in basic research as a tool for evaluating human brain function
Post-hoc tests showed that the pain threshold for Broca’s area (BA) was significantly lower than both the pain threshold for M1 and the motor threshold (MT), and that the pain threshold for M1 was significantly lower than the MT (p < 0.001)
The present study quantitatively evaluated pain thresholds for single-pulse TMS delivered to M1 and BA, and compared them with MT
Summary
Transcranial magnetic stimulation (TMS) is widely used in basic research as a tool for evaluating human brain function. TMS causes head and face muscles to contract and stimulates cutaneous fibers, which often leads to pain or discomfort on the scalp (Wassermann, 1998; Rumi et al, 2005; Rossi et al, 2009). This side effect of TMS influences aspects of task performance such as accuracy and reaction time (Abler et al, 2005; Meteyard and Holmes, 2018), and to interfere with successful completion of experiments (Wassermann, 1998; Satow et al, 2002). Even though researchers have assessed the degree of pain and the area in which pain is perceived when a certain intensity of TMS is applied
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