Capgras syndrome is a condition where a person thinks that someone they know, like a family member or friend, has been replaced by an imposter or a fake version of themselves. It might feel like the person they know has been copied and the copy is pretending to be them. It's kind of like when you play with stuffed animals and pretend they're real, but in this case, the person thinks the thing they're imagining is really happening.
Capgras syndrome can happen for different reasons, but usually it's because of a problem in the brain. Part of your brain called the amygdala helps you recognize people's faces and emotions when you see them. But if something is wrong with the amygdala, you might still recognize someone's face, but you won't feel like you know them. That's when it can seem like somebody else is pretending to be the person you know.
It can be scary and confusing for the person with Capgras syndrome, and it can be hard for their loved ones to understand why they think those thoughts. But with the help of doctors and therapists, people with Capgras syndrome can learn to manage their feelings and figure out what's happening in their brain.