In the novel, The Echo Maker, by Richard Powers, the main character, Mark, is recovering from a traumatic brain injury and begins to believe his sister is an imposter. “My sister? You think you’re my sister?” His eyes drilled her. “If you think you’re my sister, there’s something wrong with your head.” The story continues, “Days later Mark was still denying her. He assembled everything else, who he was, where he worked, what had happened to him. But he insisted that Karen was an actress who looks very much like his sister. After many tests, Dr. Hayes gave it a name. “Your brother is manifesting a condition called Capgras syndrome.” 

What is Capgras Syndrome?

Capgras syndrome is a persistent delusion that a familiar person, often a spouse or close family member, has been replaced by an identical imposter. 

Keith A. Josephs, MD, a professor of neurology and neuroscience at the Mayo Clinic in Rochester, MN, saw his first patient with Capgras syndrome early in his career. “I had a patient who would not eat dinner with his wife, because he did not think she was his wife,” he says. Years later, Dr. Joseph had another patient who misidentified her sisters. “When I walked into the room, this woman was sitting on the couch, and her sisters were huddled together, separated from her. They looked scared. As I interviewed the patient, I realized she had Capgras syndrome, and she thought her sisters were imposters. She was very mean to them. She really believed her delusion.” Yet another of his patients believed he was married to two different women. “He contacted his priest and told him he needed forgiveness from God.” 

A few years after his first case, Dr. Josephs researched Capgras syndrome and discovered that most cases were due to neurodegenerative diseases. He examined the medical records of 47 patients diagnosed with Capgras syndrome and found that 38 people had a neurodegenerative disease. More than half of the patients (26) had Lewy body dementia (LBD). LBD includes people with Parkinson's disease who later develop Parkinson's disease dementia. It also includes people with dementia with Lewy bodies, where movement problems, mood changes, and decline in thinking and memory happen together.

In 2025, Dr. Josephs and colleagues revisited the topic. Their study confirmed the original findings and added new insights. They analyzed medical records of 204 patients diagnosed with Capgras syndrome over 28 years and found that 69 percent had neurodegenerative diseases—58 percent alone had LBD. A small set, 10 percent, had Alzheimer’s disease. In 95 percent of cases, the focus of the delusion was the patient’s spouse. In people with a primary psychiatric disorder, the spouse was rarely the focus, and a variety of people were believed to be imposters, related to a more generalized paranoia. This is different from Capgras syndrome.

While delusions are common in people with dementia—believing you are dead and also alive, thinking you are infested with bugs, or believing you are living in the White House—Capras syndrome is oddly specific. “Patients usually say that the person in front of them is an imposter and that the real person is somewhere else,” explains the study co-author, Hiroyuki Watanabe, PhD, an assistant professor of neurology at the Mayo Clinic in Rochester, MN. Although it was first identified more than a century ago, Capgras syndrome is still not fully understood, likely because of how rare it is. 

A Familiar Face You Don’t Accept 

“Neurologically, Capgras syndrome is thought to occur when the brain systems responsible for recognizing faces remain relatively intact, but the emotional sense of familiarity toward that person is disturbed,” explains Dr. Watanabe. Researchers are still learning how the brain is affected. 

“I believe the right frontal lobe plays a key role,” says Dr. Josephs. “The frontal lobe is very complex—it’s not linked to one specific function, like the occipital lobe, an area that specifically deals with vision.” He adds, “The frontal lobe integrates information and is necessary for the logical interpretation of meaning. [In Capgras syndrome], the brain latches onto a new understanding that makes sense to the individual, even if it doesn’t make sense to the rest of us.” 

Research in patients with brain lesions, such as those caused by stroke, may help explain this syndrome. In a 2017 study, researchers analyzed 17 individuals with Capgras syndrome and related syndromes who had focal brain damage. In all 17 patients, the damage was connected to the left retrosplenial cortex, “your familiarity detector,” explains Michael D. Fox, MD, PhD, director of the Center for Brain Circuit Therapeutics at Brigham Women’s Hospital in Boston, MA. “With healthy people, when they see something that is familiar, that area will light up.” But 16 of the 17 also had damage to the right frontal cortex, “your reality monitor,” says Dr. Fox. “If I showed you, for example, a cat with a hammer growing out of its head, you would know that doesn’t make a lot of sense—and it’s that area that will light up.” 

Dr. Fox believes the combination of the two dysfunctional areas can lead to a Capgras delusion. You recognize your loved one’s face, yet it feels unfamiliar, and your “reality monitor” fails to help you know if your interpretation makes sense. This combination of problems allows you to believe your loved one is an imposter. 

Other studies, Dr. Fox notes, have found that brain lesions that cause behavioral changes are similar to those seen in neurodegenerative disorders. He believes that mapping brain pathways may lead to new treatments for Capgras syndrome, such as deep brain stimulation used in Parkinson’s disease or transcranial magnetic stimulation used for depression that does not improve with standard treatment. 

Helping Families Understand Capgras Syndrome

While the scientific investigations are fascinating, neurologists who have treated patients with Capgras syndrome emphasize that it is a challenging condition, both for the patient and the loved one. It can be very isolating. That’s one reason why researchers want the public to become more familiar with Capgras syndrome. 

Because the delusion tends to emerge fairly early in LBD, researchers believe identifying it may help with early diagnosis and treatment. “If you have friends or family members with this condition, it’s important to bring it to the attention of your physician, because we can help with either pharmacological medicines or behavioral interventions or a combination,” says Dr. Josephs. “In certain communities, certain cultures, this could be perceived as embarrassing, even demonic, so there’s fear to bring it to the physician. But there should be no embarrassment. The patient has no control. It’s part of the degenerative process of the brain. There is a lot of distress to the family—you can imagine how distressful this would be. Sometimes, even if you can’t treat it, just acknowledging it and explaining it to the caregivers, what it is and why it’s happening, can make a world of difference.”  

LBD is often treated with cholinesterase inhibitors—a group of medications that slow the breakdown of a brain chemical that helps with memory and thinking. In 2025, Dr. Josephs and the research team found that about 15 percent of people who took cholinesterase inhibitors had improvements in their Capgras syndrome symptoms. Low doses of certain antipsychotic medications may help, such as pimavanserin—a medication approved for treatment of delusions in Parkinson’s disease and is often prescribed for LBD.

Psychological counseling is important. People who care for a loved one with Capras syndrome are encouraged not to argue with the delusion or try to prove that you really are the spouse. “It’s a false belief and you can’t convince them otherwise,” says James E. Galvin, MD, MPH, professor of neurology and principal investigator for the Lewy Body Dementia Research Center of Excellence at the University of Miami. “Arguing can lead to agitation, aggression, irritability.” Instead, he says, “We teach the spouse skills to distract and redirect.” 

Research has found that anxiety plays a key role in the expression of Capgras delusions. Dr. Galvin hypothesizes that people with LBD begin to experience hallucinations, which leads to anxiety, and causes them to distrust what they see. “Then they focus their delusion on the person they see the most: the spouse.” In Dr. Josephs’ 2025 study, 55 percent of patients with Capgras syndrome experienced depression or anxiety. According to Dr. Watanabe, “We often see these psychiatric symptoms of Capgras syndrome get worse in the evening. I believe this is related to negative emotions, so reducing stressful or frightening stimuli—like horror movies—may help.”

Capgras syndrome can be very stressful for the spouse, but Dr. Watanabe believes that, ironically, the delusion may stem from the strength of the marital relationship. The individual isn’t rejecting the spouse but rather is attempting to maintain the relationship, he explains. “The patient doesn’t say the spouse is dead or ill, just away—he or she exists somewhere. I think this reflects a feeling of love.”