At a different institution, DBS failed to help another man with obesity. Yet he experienced a surprising side effect as soon as the electrodes were turned on. Suddenly, he was overtaken by vivid memories from 30 years prior, and when the stimulation was increased his recollections became more intense. This man did not lose any weight (in part because he turned the device off at night to binge), but his experience made investigators curious about how stimulation might enhance memory. Now a larger experiment is under way to see if DBS can help reverse the effects of Alzheimer's disease. In this case, one man's unsuccessful surgery opened up a new avenue of research, but one could imagine a scenario in which the retrieval of painful memories brings back old trauma. Such potential risks underscore the uncertainty inherent to DBS today.
Cause for Caution
Indeed, some bioethicists contend that not enough is known about DBS to broaden its use so quickly, and they call for further studies in animal models and in better-understood conditions first. The selection of some stimulation sites, as in the Alzheimer's and addiction trials, has been driven not by theory so much as happenstance. Even the fundamental mechanisms of DBS remain elusive. Initially researchers thought that it produced the equivalent of a lesion by deactivating brain areas, but it is now clear that the effects are more complicated.
The quality of the trials themselves has also come into question. Recently single-person case reports have proliferated, which are less useful than larger, placebo-controlled clinical studies. The device maker Medtronic contributed to this trend when it obtained a “Humanitarian Device Exemption” from the Food and Drug Administration, which permits the company to apply DBS to obsessive-compulsive disorder. In doing so, Medtronic sidestepped the FDA's usual channels, which would have required more rigorous experiments to establish DBS's effectiveness for this illness.
A leading concern with this piecemeal approach is that it is not clear which patients are best suited to psychiatric DBS. In several cases, patients chose to receive a stimulator before they had tried all other treatments that might have assuaged their conditions. For example, the obese man who turned off his implant so that he could binge had declined bariatric surgery—in fact, he had justified his decision by arguing that he would continue to overeat after the procedure—so perhaps it is no surprise that he went on to fiddle with his device.
Ultimately the reason we do experiments at all is because questions remain about whether new techniques and technologies truly work. Case reports may not seem dangerous, especially when the procedure seems effective. Yet using DBS outside of careful clinical trials might obscure unknown risks or side effects, such as more subtle changes to someone's thinking or behavior. Further, successful trials are more likely to be published while unknown numbers of failed attempts go unreported, skewing our scientific understanding. The incentive to develop new psychiatric treatments is enormous—approximately 50 percent of people will meet criteria for a psychiatric disorder at some point in their life—but sound science must counterbalance this drive to expand DBS.
One last example: Spanish investigators recently used DBS in six people with intellectual disabilities to curtail their out-of-control aggressiveness. The intention was to prevent harmful behavior. Yet conducting brain surgery on individuals with mental disabilities will very likely alarm the public no matter the circumstances. The promise of psychiatric DBS is immense, but considering psychosurgery's dubious past, today's practitioners must proceed with caution.