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05/01/2018

Deep Brain Stimulation: the New Mood Modifier?

A patient of mine recently had a deep brain stimulator (DBS) placed to reduce her severe tremors. The stimulator has worked very well to almost eliminate her tremor but has resulted in a side effect that causes her personality to be more impulsive. Her husband notices this more than the patient. Both agree that the reduction in the tremor outweigh the change in her personality though her husband has indicated that her personality change has been more than he imagined when they were initially considering the surgery. He has commented that if her new impulsivity were any stronger, he might be inclined to reverse the process. As one might imagine, the patient sees no problem with the impulsivity and remains extremely pleased with her newfound lack of tremor.

I share the preceding clinical vignette as backdrop to a recent article in Nature describing research funded by the US military’s research agency, The Defense Advance Research Projects Agency (DARPA – the same group that sponsored the early development of the Internet), where they are looking into modifying neural activity with the goal to alter mood, and eventually cure mental health disorders. Using patients that already have DBS stimulators in place for treatment of epilepsy or movement disorders such as Parkinson’s Disease, scientists are developing algorithms that “decode” a person’s changing mood. Edward Chang, a neuroscientist at the University of California, San Francisco (UCSF) believe they have a preliminary “mood map” and further believe that they can use the DBS stimulators to stimulate the brain and modify the local brain activity to alter the patient’s mood. The UCSF group describes this as a “closed-loop” (using the stimulator to both receive and then stimulate the brain). Chang further admits that they have already “tested some closed-loop stimulation in people, but declined to provide details because the work is preliminary.”

If scientists are on the verge of changing your mood, might they not also be on the verge of creating your urges? Professor Laura Cabrera, a neuroethicist, and Professor Jennifer Carter-Johnson, a lawyer, both at Michigan State University, argue we need to begin worrying about that possibility and further that we need to begin considering who is responsible for those new urges, particularly if those urges result in actions that cause harm against other people. The article does a masterful job of the ethical-legal ramifications of just what happens when your DBS causes you to swerve your car into a crowd of people – Is it your fault or did your DBS make you do it?

Returning to my patient, the alteration in her behavior is an unwanted but not a completely surprising result of her DBS to treat her movement disorder. Despite the informed consent, her husband was not prepared for the change in her personality. The treatment to correct my patient’s movement disorder (a good thing) has altered my patient’s personality (a not-so-good thing). My patient’s husband might even argue that his wife is almost a different person post DBS.

When we modify the brain in these experiments, we are intentionally modifying behavior but also risk modifying the person’s actual identity – the “who we are”. As the DARPA experiments proceed and cascade into spin-off research arms, we need to be very clear with patient-subjects in current and future informed consents that the patient who signs the consent may end up very different from the patient who completes the experiment. How much difference in behavior or urges should we tolerate? Could the changes be significant enough that they are considered a new person by their family and friends?

And if that is true, who should consent to the experiment?

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