Transcranial Direct Current Stimulation (tDCS) in the Treatment of Major Depressive Disorder (MDD)

Major depression is a disorder with major clinical and economic significance locally and internationally. It is a disorder of high prevalence and results in substantial disease burden and health-care costs. Critically, a significant percentage of patients, usually estimated at around 30%, fail to respond to standard treatments (Fitzgerald 2003). Techniques, such as repetitive transcranial magnetic stimulation (rTMS), are being investigated widely for the treatment of this disorder, with considerable success in recent years (Fitzgerald, Benitez et al. 2006; Hasey 2001). However, TMS equipment is expensive and requires specialized application. Additionally, TMS is associated with some side-effects (e.g. seizures). Given that depression occurs in all cultures and countries, there would be considerable value in developing a low-cost, non-invasive technique that can be applied in a wide variety of settings and which has already been shown to have some efficacy in MDD (Boggio et al. 2007).

The proposed study will be a randomized, double blind, placebo-controlled (i.e., sham stimulation vs. active tDCS), longitudinal, treatment outcome trial. Individuals with MDD will be randomized to 1 of 2 treatment conditions. These will be:

• Active 2mA tDCS: in this condition, 1 stimulator will be used with anodal stimulation to the left prefrontal cortex and cathodal stimulation to the right prefrontal cortex. The placement of anodal stimulation is proposed to enhance activity in the left frontal cortex; the cathode aims to reduce activity in the right prefrontal cortex.
• Sham treatment: the system setup is identical to that of active tDCS, but the stimulator will be turned off after 30 seconds.

A total of 15 treatments will be administered to all participants over 3 weeks (one per working day). Individuals will be randomized on a computer-generated list. Clinical raters and patients will be blind to the treatment condition. Clinical ratings well be conducted prior to and after the treatment course (i.e., after 3 weeks). All subjects randomized to sham treatment will be offered active treatment at the end of the acute treatment phase.

Inclusion criteria

• Competent to consent
• Have a diagnosis of Major Depressive Disorder and are currently experiencing a Major Depressive Episode as confirmed by the SCID-IV
• Treatment resistant, defined as a failure to achieve a clinical response, or an inability to tolerate, at least two trials of antidepressant medication of sufficient dose for at least 6 weeks
• Aged 18 to 75.
• Concomitant medications including: benzodiazepines, mood stabilizers antidepressants and anticholinergics will be allowed. Since carbamazepine has been shown to interfere with the effects of anodal tDCS, potential participants taking it will not be suitable for inclusion in the trial.

Exclusion criteria

• DSM-IV history of substance abuse or dependence in the last 6 months
• A major and/or unstable medical or neurologic illness
• Currently taking carbamazepine
• Pregnancy
• History of seizures.