There are a number of studies on Deep Brain Stimulation going on. St. Jude's & Medtronics are both racing to better understand the possibilities.
http://www.broadenstudy.com (actual study)
http://www.medscape.com/viewarticle/520659
http://www.shockmd.com/2008/09/04/deep-brain-stimulation-for-depression (video)
278-005.blogspot.com (An actual study participant)
http://www.medicalnewstoday.com/articles/104908.php
I believe it's been installed on over 40,000 Parkinson's sufferers to relieve the tremors, but programming the units seems to be an art, not a science yet. Regardless, it is FDA approved for that.
http://www.dbs-stn.org/articlesdetails.php?ID=3
Neuropsychology is in its infancy.