A response to this post:
I think the author of this post is quite right to ask questions about the nature of evidence of these radically invasive, bio-reductionists ‘treatments’ for depression.
Whilst depression and its cognate conditions (melancholy, acedia, and others) have always had biological correlates, they have always been defined in terms of a subjective disposition. (This is the case with all affects, of which we can understand the depressions to constitute a subset). Even in the DSM system, this subjective element remains the sine qua non condition of diagnosis.
Having misdefined depression, DBS then literally mistreats it. See this, for instance:
http://neurocritic.blogspot.com.au/2014/01/broaden-trial-of-dbs-for-treatment.html
The problem here isn’t so much the medical problem, as a fundementally shoddy conceptualisation of depression. Politically incorrect as it may be to say it, it is a condition in which a subject is implicated. The bioreductionists want to bypass this subject/ivity, treating people as mere objects.
It’s not that bio-interventions are all bad – good diet and exercise, for instance, are beneficial among the depressed as for everybody else – it’s that they are not cures, and moreover, they completely elide the singularity of each subject’s depression.
So too for meds. There are, strictly speaking, no ‘antidepressants’, only SSRIs and SNRIs, whose subjective effects are highly ambiguous and variable.
As ever in the psy disciplines, there is little point in technological overreach if your ‘science’ is not matched with an equally complex understanding of language.
Archives of a Divided Subject 
Although there is continuing research on the topic, the traumatic nature of mental disease is ignored in psychiatry and most of psychology. Most practitioners end up further traumatizing their patients.