Monday, January 09, 2006

Update on Deep Brain Stimulation

I wrote about this at some length previously.  Those interested in the experimental deep brain stimulator, being developed as a treatment for Major Depression, may be interested in a Medscape interview with Dr. Helen Mayberg, one of the investigators.  The interview provides some background on the treatment and how it was developed:
Our original hypothesis was that stimulation of the subgenual cingulate region would disrupt activity in the subgenual cingulate cortex and produce secondary remote effects in brain regions functionally linked to this region via adjacent white-matter fibers. On the basis of these known connections, we anticipated potential changes in the brain stem, hypothalamus, nucleus accumbens, and various regions of the orbital, medial, and prefrontal cortex.

We also had previous imaging evidence that the activity in this multinodal depression "circuit" was dysfunctional. We therefore saw DBS as a means to influence the balance between this highly interactive set of brain regions at the level of the subgenual cingulate.
Further in the interview, we learn that six more patients are getting this experimental treatment, in addition to the six already studied.  To me, the most interesting part of the interview was this exchange, in which Dr. Mayberg described the experiences of the patients:

Medscape: One of the major differences between what you're seeing here with DBS and what is observed with other treatments for depression is the acute effects. Can you describe some of the acute effects of stimulation?

Dr. Mayberg: The acute effects in the operating room were unique for each patient, but all shared certain features. In general, patients described a sudden disappearance of something negative, which was more often than not a change in a visceral state: a sudden sense of intense calm and relief, clearing of mental heaviness, lifting of a black cloud, the disappearance of a void, fading of a burrowing dread in the pit of the stomach, are some examples. Of interest, the turning off of these negative sensations was followed almost immediately by a change in attention and interest with objective evidence of increased spontaneous speech and motor speed. Such effects, when present, were contact- and dose-specific and could be reproduced in a blinded fashion with repeated testing. Their time course was quite rapid, occurring approximately 15-20 seconds after initiating stimulation at the specific electrode contact.

Importantly, the mood effects were quite specific. Patients did not experience positive mood effects; rather, their chronic negative mood was attenuated. [...]
The reason this is so important, is that is both highlights and refutes a common misunderstanding about the treatment of depression.  No existing treatment actually elevates mood, or causes euphoria.  When successful, treatment of depression merely eliminates pathological negative mood states.  It does not give the patients anything they did not have to begin with.  

Another interesting aspect of this research is that it may help us understand more about consciousness and emotional experience in general, not just in persons with mental illness.