The Depression Circuit

One of the most intriguing developments in the field of neuromodulation in recent years has been the quest to identify the neural circuits involved with mood disorders. As we discuss in our article on page 1 of this issue, deep brain stimulation in general, and DBS for treatment of Parkinson’s disease in particular, has proven to be a powerful tool for neurologists and psychiatrists studying psychiatric disorders. We believe that the results of these efforts will have profound effects on the ease with which new neurotechnology therapies gain regulatory approval and clinician, patient, and insurer acceptance,

The experience of Cyberonics in the years leading up to and the year subsequent to FDA approval of VNS for treatment resistant depression offers a telling example. Despite gaining FDA approval, the company continues to draw criticism from naysayers who question the less than perfect response rate, the lack of understanding of neurological mechanism, and the magnitude of placebo effect. Despite the fact that more than 3000 psychiatrists have shown interest in VNS therapy, Cyberonics is still fighting an uphill battle to get insurance reimbursement.

There seems to be more than a little irony in some of this criticism. If understanding the precise neural mechanism of a psychiatric therapy were a firm requirement, very few antidepressant drugs would be on the market and ECT would be banned. And while response rates of 30 to 50 percent for patients with treatment resistant depression may seem low, let’s not forget that those same patients would respond 0 percent to any of the neuropharmaceuticals currently on the market.

We also think that regulators and the public should not be so quick to dismiss placebo effects of neurostimulation devices, particularly if there is a differential effect between drugs and devices. Some researchers have begun to identify neurological changes that accompany placebo effects, and if a therapy such as VNS can enhance this effect, relative to drugs, then so much the better.

Plus, it’s worth noting that psychiatric surgical interventions such as cingulotomy and capsulotomy have been found by some studies to have a response rate of 30 to 40 percent. Given the reversible nature of neurostimulation, the advent of neuromodulation for highly refractive psychiatric disorders should be seen as an attractive alternative.

Still, the eventual identification of what Helen Mayberg calls the “circuit board for depression” will be a boon for all neuromodulation vendors. Presumably, this increased understanding will enable clinicians to tailor the stimulation regimen to the particular circuit or circuits that are faulty, and in so doing, raise the response rates for all therapies. Unfortunately, it may be difficult to reach this point if regulators and insurers fail to recognize the unique opportunity that neurostimulation offers.

James Cavuoto
Editor and Publisher