Subjective Discomfort of TMS Predicts Reaction Times Differences in Published Studies

Transcranial magnetic stimulation (TMS) was developed thirty years ago, in part to decrease the peripheral side-effects associated with transcranial electrical stimulation (Barker, 1991). TMS has been effective in that aim, and great advances have been made over the past 30 years. TMS can still be uncomfortable and painful, however, as it stimulates excitable superficial tissue including scalp muscles and peripheral nerves (Maizey et al., 2013). This causes annoyance, pain, and muscle twitches (i.e., discomfort) that vary systematically across the scalp (Meteyard & Holmes, 2018). For this Opinion, we investigated whether the TMS-related discomfort measured in our previous work could predict the reported differences in RT in studies published in the last 10 years. For single-pulse TMS studies, differences in RT between TMS and control conditions were significantly correlated with both the mean of median ratings of muscle twitches, and the mean effect of TMS on RT from Meteyard & Holmes (2018).