Non-invasive brain stimulation therapies have been increasingly investigated in recent years as a treatment for neuropsychiatric disorders, particularly mood disorders. They are particularly appealing since many patients are either refractory or present side effects to standard pharmacological regimens. TDCS (transcranial direct current stimulation). a novel non- pharmacological brain stimulation technique, might help in overcoming some of these issues, since it has low cost, high portability and it is relatively easy to use. TDCS consists in applying a weak, direct current through two electrodes placed over the scalp; the anode and the cathode increasing and decreasing cortical excitability during and beyond the period of stimulation. It is also a safe technique with only mild adverse effects described. Previous studies, some of them from our group, have described that tDCS is an effective technique for major depression. However, the role of tDCS as a treatment for bipolar depression (BD) has been insufficiently investigated. Therefore, our aim is to address the antidepressant effects of tDCS in BD in a randomized, sham- controlled trial in a refractory sample.

BD represents the greatest burden on patients with bipolar disorder, since the depressive episodes are the most frequent and also particularly associated with suicide 7. BD treatment is controversial, with some stricter guidelines recommending only lithium, lamotrigine and quetiapine as a first-treatment, whereas others allow the use of antidepressants (which can increase manic switch and should be used in association with mood stabilizers) and other anticonvulsants and antipsychotics 8. For refractory BD the available level I evidence is very scarce, with only seven studies exploring this issue hitherto 9. Therefore, the importance of this study proposal is justified considering the burden of the disease, the paucity of current therapeutic studies and the promising results presented for tDCS in unipolar disorder.

Inclusion Criteria:

• bipolar depressed (type I, II or not otherwise specified) participants with symptoms in spite of an adequate treatment course with mood stabilizers.
• the depressive episode has to be of at least moderate intensity (baseline HDRS>=16)
• read and understand Portuguese

Exclusion Criteria:

• other neuropsychiatric conditions, such as schizophrenia, substance dependence, dementias, traumatic brain injury, epilepsy and so forth (although participants with anxiety disorders can be included whether the primary diagnosis is BDD);
• mixed states, defined as simultaneously presenting (hypo)manic symptoms with a Young Manic Rating Scale (YMRS) > 8;
• pregnancy;
• specific contra-indications to tDCS;
• severe/life-threatening clinical conditions. Participants will have to be drug-free or at stable drug regimen for at least 6 weeks prior to trial onset. Benzodiazepine drugs will be allowed, although only at low doses (less than 20mg/day of diazepam or equivalent).