4. treatment resistance depression as defined as report of inadequate response (patient report of minimal improvement or nonresponse) despite past treatment with at least 2 different classes of antidepressants acting on the 5-HT and/or DA monoamine systems(except MAOIs) (as determined with the Antidepressant Treatment History Form (ATHF)20 with score of >3 on each of the items and verified by medical records if available);