In response to Larsen's laughter, a staff member in the operating room asked him what he was feeling. Larsen said, "I don't know why, but I feel happy. I feel like laughing."
Doctors continued probing his brain for hours, figuring out what areas -- and what level of stimulation -- might work weeks later, when Larsen would have his device turned on for good.
In the weeks after surgery, the residual swelling in his brain kept those good feelings going. For the first time in years, Larsen and his mother had hope for normalcy.
"I know that Brett has a lot of normal in him, even though this disease eats him up at times," said Michele Larsen. "There are moments when he's free enough of anxiety that he can express that. But it's only moments. It's not days. It's not hours. It's not enough."
Turning it on
In January, Larsen had his device activated. Almost immediately, he felt a swell of happiness reminiscent of what he had felt in the OR weeks earlier.
But that feeling would be fleeting -- the process for getting him to an optimal level would take months. Every few weeks doctors increased the electrical current.
"Each time I go back it feels better," Larsen said. "I'm more calm every time they turn it up."
With time, some of his compulsive behaviors became less pronounced. In May, several weeks after his device was activated, he could put on his shoes with ease. He no longer spun them around in an incessant circle to allay his anxiety.
But other behaviors -- such as turning on and shutting off the faucet -- continued. Today, things are better, but not completely normal.
Normal, by society's definition, is not the outcome Larsen should expect, experts say. Patients with an intractable disease who undergo deep brain stimulation should expect to have manageable OCD.
Lately, Larsen feels less trapped by his mind. He is able to make the once interminable trek outside his home within minutes, not hours. He has been to Disneyland with friends twice. He takes long rides along the beach to relax.
In his mind, the future looks bright.
"I feel like I'm getting better every day," said Larsen, adding that things like going back to school or working now feel within his grasp. "I feel like I'm more able to achieve the things I want to do since I had the surgery."