A paper which appeared in Neuroscience & Biobehavioral Reviews reports data showing that all currently researched DBS targets for depression - which all lead to comparable response rates in patient populations with comparable treatment refractoriness - actually stimulate in close proximity to the medial forebrain bundle (MFB) pointing to the possibility that this structure might be involved in mediating antidepressant effects. Full reference below.
Volker A. Coenen, Thomas E. Schlaepfer, Burkhard Maedler, Jaak Panksepp. Cross-species affective functions of the medial forebrain bundle—Implications for the treatment of affective pain and depression in humans. Neuroscience & Biobehavioral Reviews, 2010; DOI: 10.1016/j.neubiorev.2010.12.009