A man survives a stroke and his life returns to normal, except he harbors one mysterious belief: He’s convinced his mother is an imposter who happens to look just like the original. This delusion was first described in 1923 by French psychiatrist Joseph Capgras, but its neurological underpinnings are only now being understood, said neuroscientist Vilayanur S. Ramachandran, MD, PhD, director of the Center for Brain and Cognition at the University of California, San Diego.

Some believe the condition — known as the Capgras syndrome — arises from people’s need to suppress subconscious sexual desire for their mothers — if that woman isn’t, in fact, one’s mother, feelings of attraction are OK. Capgras can also occur with people’s spouses, children or other loved ones. Ramachandran saw one Capgras patient who thought his poodle was an imposter. “I don’t know how Freudians would explain that one,” he said.

Research by Ramachandran and others suggests an alternative explanation. It seems that in healthy people, the brain’s visual cortex relays information through two routes, one that goes to the temporal lobe, where face recognition occurs, and one that goes to the limbic system, which registers an emotional reaction. In Capgras patients, the route from the visual cortex to the limbic system is damaged, but the route to the temporal lobe remains unharmed, causing the person to see a woman who looks like his mother, but who sparks no emotional response. The mind explains that discrepancy by insisting that the woman is an imposter, Ramachandran posits.

To test this theory, Ramachandran and his colleague, philosopher William Hirstein, PhD, recorded a Capgras patient’s emotional reaction to photographs of loved ones — via measures of skin conductance — and found his emotional response stayed level while he viewed photographs of loved ones and strangers. In comparison, control group members showed sharp increases in skin conductance when they viewed pictures of their mothers versus strangers.

In addition to thinking that one’s loved ones are imposters, people who experience a visual-emotional disconnect may lose some of their aesthetic appreciation, said Ramachandran.

“Interestingly, Capgras patients also report losing interest in art, in paintings,” he said.

—S. Dingfelder