This study aims to investigate the potential for Transcranial Direct Current Stimulation (tDCS) to enhance cognitive functioning in euthymic bipolar patients through comparing the effect of active or sham tDCS (placebo control) during the performance of two cognitive tasks. The investigators hypothesize that task performance will be improved with active relative to sham tDCS.

Inclusion Criteria:

• Participants will be right-handed subjects aged 18-65 meeting DSM-IV diagnostic criteria for bipolar disorder, with no acute episodes of depression or mania within the previous 12 weeks
• A score of ≤ 20 on the MADRS, and a score of ≤ 6 on the YMRS, who have been on a stable dose of mood stabiliser medications for at least 1 month.

Exclusion Criteria:

• Patients with high suicide risk
• Co-morbid DSM-IV diagnosis of any psychotic disorder (current or within the last year), schizophrenia and schizoaffective disorder
• Mental retardation
• A history of drug or alcohol abuse or dependence within the last 3 months
• Co-morbid attention deficit hyperactivity disorder (ADHD), or any neurological disorder
• Recent stroke
• Head injury
• History of seizure, or who have had electroconvulsive therapy (ECT) within the 6 months preceding enrolment.
• Participants will also be excluded if currently taking medications known to be associated with frank cognitive impairment (e.g., benzodiazepines).