The two began with a single volt. Not much happened. The patient’s well-being or “happiness level” was down around two, while his anxiety was up at eight. With another volt, his happiness level crawled up to three, and his anxiety fell to six. That was better but still nothing to write home about. At four volts, on the other hand, the picture was entirely different. The patient now described a feeling of happiness all the way up to the maximum of 10 and a total absence of anxiety.

“It’s like being high on drugs,” he told Synofzik. The neurologist turned up the voltage one more notch for the sake of the experiment, but at five volts the patient said that the feeling was “fantastic but a bit too much.” He had a feeling of ecstasy that was almost out of control, which made his sense of anxiety shoot up to seven.

The two agreed to set the stimulator at three volts, which left the patient at a “normal” level of happiness and anxiety, and would not exhaust the $5,000 battery too quickly. But the next day, when the patient was to be discharged, he went to Synofzik and asked whether they might not turn the voltage up anyway before he went home. He felt fine, but he also felt that he needed to be a “little happier” in the weeks to come. The neurologist refused. The patient finally gave in and went home in his median state with an agreement to return for regular checkups.

“It is clear that doctors are not obligated to set parameters beyond established therapeutic levels just because the patient wants it,” Synofzik and his two colleagues wrote in their article. After all, patients “don’t decide how to calibrate a heart pacemaker.”

It seems the unknown young man with accumbens electrodes didn’t buy the argument because, after a short time, he stopped coming in for checkups and vanished without a trace. Maybe he found another doctor who was willing to make him happy.

In 2005, the American neurologist Helen Mayberg and the Canadian surgeon Andres Lozano published the first study of deep-brain stimulation for the treatment of severe chronic depression—the kind of depression that does not respond to anything: not medicine, not combinations of medicine and psychotherapy, not electric shock. Yet six patients on whom everyone had given up suddenly got better.

“It’s not my job as a neurologist to make people happy.” Helen Mayberg let her statement hang in the air between us before she continued. “I liberate my patients from pain and counteract the progress of disease. I pull them up out of a hole and bring them from minus 10 to zero, but from there the responsibility is their own. They wake up to their own lives and to the question: Who am I?”

Mayberg focused on a little area of the cerebral cortex with a gnarly name, the area subgenualis or Brodmann area 25. It is located near the base of the brain almost exactly behind the eye sockets. Here, it is connected not only to other parts of the cortex, but to parts of the reward system and of the limbic system, brain regions involved with our motivation, our experience of fear, our learning abilities and memory, libido, regulation of sleep, appetite—everything that is affected when you are clinically depressed.