Trial of Transcranial Direct Current Stimulation (tDCS)

Inclusion Criteria: * Subject meets criteria for a DSM-IV Major Depressive Episode. * Total MADRS score ≥20. Exclusion Criteria: * Diagnosis (as defined by DSM-IV) of: any psychotic disorder (lifetime); eating disorder (current or within the past year); obsessive compulsive disorder (lifetime); post-traumatic stress disorder (current or within the past year); mental retardation. * History of drug or alcohol abuse or dependence (as per DSM-IV criteria) within the last 3 months (except nicotine and caffeine). * Inadequate response to ECT in the current episode of depression. * Subject is on regular benzodiazepine medication which it is not clinically appropriate to discontinue. * Subject requires a rapid clinical response due to inanition, psychosis or high suicide risk. * Neurological disorder or insult, e.g., recent stroke (CVA), which places subject at risk of seizure or neuronal damage with tDCS. * Subject has metal in the cranium, skull defects, or skin lesions on scalp (cuts, abrasions, rash) at proposed electrode sites. * Female subject who is pregnant. * Participants who are not fluent in English will not be included in the trial for safety reasons: a) It is usually not possible to have an interpreter reliably available every weekday for up to 4 weeks and it is not safe to give tDCS to a subject who cannot tell us immediately of any side effects; b) As this is a novel treatment, the study involves detailed neuropsychological testing for safety reasons. This testing cannot be effectively or validly completed by someone who is not fluent in English. Note that translation of the proposed tests into English has not been validated and that we cannot be confident that neuropsychological impairment would be detected using this method.