TITLE
Pulse Width Affects Scalp Sensation of Transcranial Magnetic Stimulation

AUTHORS
Peterchev AV; Luber B; Westin GG; Lisanby SH. Institution Peterchev, Angel V. Department of Psychiatry and Behavioral Sciences, Duke University, Durham, NC, USA; Department of Biomedical Engineering, Duke University, Durham, NC, USA; Department of Electrical and Computer Engineering, Duke University, Durham, NC, USA. Luber, Bruce. Department of Psychiatry and Behavioral Sciences, Duke University, Durham, NC, USA. Westin, Gregory G. Division of Vascular and Endovascular Surgery, New York University Langone Medical Center, New York, NY, USA. Lisanby, Sarah H. Department of Psychiatry and Behavioral Sciences, Duke University, Durham, NC, USA; Department of Psychology and Neuroscience, Duke University, Durham, NC, USA.

ELECTRONIC ADDRESS
angel.peterchev@duke.edu

SOURCE
Brain Stimulation. 10(1):99-105, 2017 Jan – Feb.

BACKGROUND
Scalp sensation and pain comprise the most common side effect of transcranial magnetic stimulation (TMS), which can reduce tolerability and complicate experimental blinding.

OBJECTIVE
We explored whether changing the width of single TMS pulses affects the quality and tolerability of the resultant somatic sensation.

METHODS
Using a controllable pulse parameter TMS device with a figure-8 coil, single monophasic magnetic pulses inducing electric field with initial phase width of 30, 60, and 120micro s were delivered in 23 healthy volunteers. Resting motor threshold of the right first dorsal interosseus was determined for each pulse width, as reported previously. Subsequently, pulses were delivered over the left dorsolateral prefrontal cortex at each of the three pulse widths at two amplitudes (100% and 120% of the pulse-width-specific motor threshold), with 20 repetitions per condition delivered in random order. After each pulse, subjects rated 0-to-10 visual analog scales for Discomfort, Sharpness, and Strength of the sensation.

RESULTS
Briefer TMS pulses with amplitude normalized to the motor threshold were perceived as slightly more uncomfortable than longer pulses (with an average 0.89 point increase on the Discomfort scale for pulse width of 30micro s compared to 120micro s). The sensation of the briefer pulses was felt to be substantially sharper (2.95 points increase for 30micro s compared to 120micro s pulse width), but not stronger than longer pulses. As expected, higher amplitude pulses increased the perceived discomfort and strength, and, to a lesser degree the perceived sharpness.

CONCLUSIONS
Our findings contradict a previously published hypothesis that briefer TMS pulses are more tolerable. We discovered that the opposite is true, which merits further study as a means of enhancing tolerability in the context of repetitive TMS.