A pilot study of the tolerability, safety and effects of high-definition transcranial direct current stimulation (HD-tDCS) on pain perception

Abstract

Several brain stimulation technologies including implantable motor cortex stimulation (MCS), transcranial magnetic stimulation (TMS) and transcranial direct current stimulation (tDCS) are beginning to evidence promise as treatments for a variety of pain conditions. While tDCS appears safe and is easy to administer, most versions of this technique involve large saline soaked pads applied over the scalp, which stimulate broad regions of cortex and are not spatially precise. A new tDCS design allows for focal delivery of the charge to discrete regions of the cortex, called High Definition tDCS (HD-tCDS). We sought to preliminarily test the safety and tolerability of the HD-tDCS technique as well as to evaluate whether HD-tDCS over the motor cortex could decrease pain and sensory experience. Twenty-four healthy adult volunteers underwent quantitative sensory testing before and after 20 minutes of real (n=13) or sham (n=11) 2 mA HD-tDCS over the right scalp area over the left body motor cortex. No adverse events occurred and no side-effects were reported following stimulation. The scalp sensations associated with stimulation included “itchiness”, “tingling”, and “prickling.” The painfulness of the stimulation-induced scalp sensations was rated as 1.98 out of 10 on average in the real stimulation group. Real HD-tDCS was associated with significantly decreased heat and cold sensory thresholds, decreased thermal wind-up pain, and a marginal analgesic effect was observed for cold pain thresholds. No significant effects were observed for mechanical pain thresholds or heat pain thresholds. Applied in this manner, HD-tDCS appears to be safe and well-tolerated, and can produce changes in underlying cortex that are associated with changes in pain perception. Future studies seem warranted to investigate HD-tDCS in other applications, and further examine its potential to affect pain perception.