A real electro-magnetic placebo (REMP) device for sham transcranial magnetic stimulation (TMS)

Abstract

Objective There is growing interest in neuropsychiatry for repetitive transcranial magnetic stimulation (rTMS) as a neuromodulatory treatment. However, there are limitations in interpreting rTMS effects as a real consequence of physiological brain changes or as placebo-mediated unspecific effects, which may be particularly strong in psychiatric patients. This is due to the fact that existing sham rTMS procedures are less than optimal. A new placebo tool is introduced here, called real electro-magnetic placebo (REMP) device, which can simulate the scalp sensation induced by the real TMS, while leaving both the visual impact and acoustic sensation of real TMS unaltered. Methods Physical, neurophysiological and behavioural variables of monophasic and biphasic single-pulse TMS and biphasic 1 Hz and 20 Hz rTMS procedures (at different intensities) were tested in subjects who were expert or naïve of TMS. Results of the real TMS were compared with those induced by the REMP device and with two other currently used sham procedures, namely the commercially available Magstim sham coil and tilting the real coil by 90°. Results The REMP device, besides producing scalp sensations similar to the real TMS, attenuated the TMS-induced electric field (as measured by a dipole probe) to a biologically inactive level. Behaviourally, neither expert nor naïve TMS subjects identified the “coil at 90°” or the “Magstim sham coil” as a real TMS intervention, whilst naïve subjects were significantly more likely to identify the REMP-attenuated TMS as real. Conclusions The “goodness of sham” of the REMP device is demonstrated by physical, neurophysiological, and behavioural results. Significance Such placebo TMS is superior to the available sham procedures when applied on subjects naïve to TMS, as in case of patients undergoing a clinical rTMS trial.