Adam Lepak looked over at his mother and said, "You're fake."
It was a Tuesday in July, late, and Cindy Lepak could see that her 19-year-old son was exhausted. Long days like this one, with hours of physical therapy and memory drills — I had a motorcycle accident, I hit my head and have trouble remembering new things, I had a motorcycle accident — often left him making these accusations.
"What do you mean 'fake,' Adam?" she said.
He hung his head. "You're not my real mom," he said. His voice changed. "I feel sorry for you, Cindy Lepak. You live in this world. You don't live in the real world."
Doctors have known for nearly 100 years that a small number of psychiatric patients become profoundly suspicious of their closest relationships, often cutting themselves off from those who love them and care for them. They may insist that their spouse is an impostor; that their grown children are body doubles; that a caregiver, a close friend, even their entire family is fake, a duplicate version.
Such delusions are often symptoms of schizophrenia. But in the last decade or so, researchers have documented similar delusions in hundreds of people who are not schizophrenic but have neurological problems including dementia, brain surgery and traumatic blows to the head.
A small group of brain scientists is now investigating misidentification syndromes, as the delusions are called, for clues to one of the most confounding problems in brain science: identity. How and where does the brain maintain the "self"? [...]