Development and evaluation of a portable sham transcranial magnetic stimulation system

Abstract

Background-Transcranial magnetic stimulation (TMS) is a relatively noninvasive brain stimulation technology that can focally stimulate the human cortex. One significant limitation of much of the TMS research to date concerns the nature of the placebo or sham conditions employed. When TMS pulses are delivered repetitively (especially prefrontal TMS) it is often experienced as painful. Most sham TMS techniques produce identical sounds to active TMS, but they do not cause much, if any, scalp or facial sensation or discomfort. This is a serious problem when investigators are attempting to evaluate the effects of TMS using traditional sham techniques because of unintended systematic differences between real and sham TMS groups (i.e., confounds). As long as traditional approaches to sham TMS are employed, the validity of the inferences regarding the efficacy of TMS will be limited. While some other sophisticated systems have been developed to address these concerns, they tend to be expensive and lack portability. Portability will likely become more and more important as TMS applications expand into different clinical areas (e.g., TMS in the postanesthesia care unit following surgery)

Repetitive transcranial magnetic stimulation (rTMS) of the dorsolateral prefrontal cortex reduces resting-state insula activity and modulates functional connectivity of the orbitofrontal cortex in cigarette smokers

“…Electrodes were connected to the Cool-B65 Butterfly Coil sham stimulator. The electrical current of the sham system using a sham rTMS coil was titrated to a level matching participants’ sensory ratings of active rTMS in order to make active and sham stimulation indistinguishable (Borckardt et al, 2008). We used 10 Hz, 5 seconds-on, 10 seconds-off for 15 minutes in sham conditions.…”

Daily Left Prefrontal Transcranial Magnetic Stimulation Therapy for Major Depressive Disorder

“…Specifically, we used intense rTMS treatment, including high-intensity stimulation (120% motor threshold [MT]), a high number of pulses (3000 stimuli per session), magnetic resonance imaging (MRI) adjustment for proper scalp placement, 52 and provision for extended treatment in patients showing clinical improvement using a duration-adaptive design. [53][54][55][56] Other methodological improvements included use of an active sham condition that mimicked the somatosensory experience of rTMS, 57,58 masking of rTMS administrators and patients to the acoustic signals produced by stimulation, requiring all outcome evaluators to undergo a competency certification process, continuous assessment of outcome evaluator reliability compared with a masked expert external rater, and constant assessment of potential unmasking.…”

Sham or real—Post hoc estimation of stimulation condition in a randomized transcranial magnetic stimulation trial

“…The acoustic artefact is present in both strategies. The sensory artefact is not present or has to be technically simulated with the sham coil [5], or it might be critically diminished when modifying a real stimulation to be ineffective. In our rTMS multi-centre trial, a modified stimulation condition for sham was chosen.…”

“…On the other hand, sham and real should not differ concerning the subjective experience of the stimulation. The first aspect can be fulfilled by dislocating the coil or using a so called "sham coil", the second one by inducing the characteristic noise and the sensory, sometimes painful artefact [5]. That sensory artefact however, is not present when using commercially available sham coils or it is of a different character when attempting to mimic the sensory impression [2].…”