Over the past few years, deep brain stimulation (DBS) has emerged as a promising treatment for severe psychiatric disorders that haven't responded to conventional approaches. A new paper from the University of Florida reports on a trial of DBS in obsessive-compulsive disorder (OCD), and unlike most DBS studies, it was placebo-controlled: Deep Brain Stimulation for Intractable Obsessive Compulsive Disorder.
Six patients were implanted with electrodes in the "ventral capsule/ventral striatum" (VC/VS). This area has previously been used as a DBS target for OCD. The original reason for choosing to implant electrodes in this region was that it's long been known that destroying the anterior limb of the internal capsule (capsulotomy) alleviates OCD symptoms in many cases, especially if the ventral (lower) part is removed.
Did it work? Yes, but not for everyone. Out of the 6 patients who entered the trial, all of whom were extremely ill despite having tried multiple medications and psychotherapy, 4 (66%) eventually responded well. The other 2 unfortunately got little or no benefit over the 12 month trial period.
The study had a double-blind, placebo-controlled phase: the patients weren't told when the DBS electrodes were going to be switched on. As the graphs show, in the 3 patients who were randomly selected to have them switched on early, 2 responded pretty much immediately, while in the 3 patients whose electrodes were left off, none responded until they were turned on 30 days later, although the response at this point was fairly gradual.
One person (S1), who responded very well initially, suddenly relapsed about a year later. Upon investigation, it turned out that the battery powering their electrodes had worn out, although no-one knew this until the OCD symptoms returned, so this can't have been a placebo effect. They recovered after getting a new battery.
Overall there are few surprises here. These results confirm what we already knew about DBS: it works in many people, but not all, with response rates of around 60%; When it works, it works very well; but sometimes the effects take weeks or months to become fully apparent. This could be either because DBS starts some gradual process of change in the brain which takes time to work; or it could be that it often takes a long time to find the right stimulation parameters (voltage, frequency, etc.) which provide a good response, since this has to be done by trial-and-error. Most likely, it's a bit of both.
What I found most interesting was that the VC/VS stimulation didn't just treat people's obsessions and compulsions. It also had a mood-improving effect, and crucially, it sounds as though mood was the first thing to improve, with OCD symptoms following days or weeks later:
and mood was the first thing that got worse when the DBS was accidentally turned off for whatever reason:
Finding the optimal settings for an individual subject proved challenging...unlike other experiences with DBS, there is not a clear positive symptom (e.g., tremor improvement) to gauge settings. In this study... the goal was to select parameters that produced some benefit in mood or anxiety symptoms acutely, with minimal side effects.
And in fact, four people experienced temporary hypomania, i.e. abnormally elevated mood, which is usually seen in bipolar disorder, although none of the patients in this study had a history of bipolar. People also commonly reported increased alertness, motivation, and difficulty falling asleep.
Worsening in mood or increased anxiety were typically the first symptoms reported following battery depletion or inadvertent inactivation by metal detectors. Other signs of depression, such as diminished energy or interest, also emerged within days of device interruption... Exacerbation of OCD symptoms generally lagged the emergence of affective or anxiety symptoms.
This all fits with the fact that VC/VS stimulation has been used as a DBS target for clinical depression, as well as for OCD. Indeed, this suggests that DBS probably works in essentially the same way in both conditions. The drugs that are used to treat OCD are all antidepressants - specifically serotonin-based ones - so this makes sense too.
With luck, research on DBS in animals and humans will finally allow us to understand the neural basis of mood states like depression, and mania - something which, despite decades of research on drugs like antidepressants and mood stabilizers, is still deeply mysterious...
Goodman, W., Foote, K., Greenberg, B., Ricciuti, N., Bauer, R., Ward, H., Shapira, N., Wu, S., Hill, C., & Rasmussen, S. (2010). Deep Brain Stimulation for Intractable Obsessive Compulsive Disorder: Pilot Study Using a Blinded, Staggered-Onset Design Biological Psychiatry, 67 (6), 535-542 DOI: 10.1016/j.biopsych.2009.11.028