Sham transcranial magnetic stimulation using electrical stimulation of the scalp

Background Most methods of sham, repetitive transcranial magnetic stimulation (rTMS) fail to replicate the look, sound, and feet of active stimulation in the absence of a significant magnetic field. Objective/hypothesis To develop and validate a new method of sham rTMS appropriate for a double-blind, placebo-controlled study with subject crossover. Methods The look and sound of active rTMS was replicated using a matched, air-cooled sham TMS coil. Scalp muscle stimulation associated with rTMS was replicated with the use of large rubber electrodes placed over selected muscles. The intensity and pulse width of electrical stimulation necessary to match 1-Hz rTMS was developed in one sample of normal, healthy subjects. The sham technique was validated in back-to-back comparisons with active rTMS in new samples of normal, healthy subjects who were either naive or experienced with rTMS. Results Subjects naive to TMS could not tell which type of stimulation was active or sham or which was electrical or magnetic. Naive subjects incorrectly picked sham stimulation as active, when forced tochoose, because electrical stimulation felt more focused than magnetic stimulation. Subjects experienced with TMS Could correctly identify sham and active stimulation. Experimenters could detect subtle differences between conditions. Conclusions This method of sham rTMS closely mimics the look, sound, and feel of active stimulation at 1Hz without creating a significant magnetic field. It is valid for use with naive subjects and in crossover studies. It can accommodate differences in scalp muscle recruitment at different sites of stimulation, and it could potentially be used with higher frequency stimulation. (C) 2009 Elsevier Inc. All rights reserved.