Neuroethics of deep brain stimulation for mental disorders: brain stimulation reward in humans

The theoretical basis of some deep brain stimulation (DBS) trials undertaken in the early years was the phenomenon of "brain stimulation reward (BSR)," which was first identified in rats. The animals appeared to be rewarded by pleasure caused by the stimulation of certain brain regions (reward system), such as the septal area. "Self-stimulation" experiments, in which rats were allowed to stimulate their own brain by pressing a freely accessible lever, they quickly learned lever pressing and sometimes continued to stimulate until they exhausted themselves. BSR was also observed with DBS of the septal area in humans. DBS trials in later years were undertaken on other theoretical bases, but unexpected BSR was sometimes induced by stimulation of some areas, such as the locus coeruleus complex. When BSR was induced, the subjects experienced feelings that were described as "cheerful," "alert," "good," "well-being," "comfort," "relaxation," "joy," or "satisfaction." Since the DBS procedure is equivalent to a "self-stimulation" experiment, they could become "addicted to the stimulation itself" or "compulsive about the stimulation," and stimulate themselves "for the entire day," "at maximum amplitude" and, in some instances, "into convulsions." DBS of the reward system has recently been applied to alleviate anhedonia in patients with refractory major depression. Although this approach appears promising, there remains a difficult problem: who can adjust their feelings and reward-oriented behavior within the normal range? With a self-stimulation procedure, the BSR may become uncontrollable. To develop DBS to the level of a standard therapy for mental disorders, we need to discuss "Who has the right to control the mental condition?" and "Who makes decisions" on "How much control is appropriate?" in daily life.