Derek Morgan:  He said his parents had been replaced .
Emily Prentiss: He just sounds delusional .
Dr. Spencer Reid: You know , he might have Capgras syndrome . It 's a delusional disorder in which one believes that their friends and loved ones have been replaced by imposters .
Derek Morgan: Sort of like Invasion of the Body Snatchers .
Dr. Spencer Reid: It typically involves only one sense , such as sight . Basically , the neural connection between the visual cortex and the emotional center of the brain becomes severed , so that looking at a loved _ one _ does n't elicit the same emotional response one would expect .
Aaron Hotchner: So , you think they 're an imposter .
Dr. Spencer Reid: And the interesting thing is that the auditory connection remains intact , so that if they were to hear a loved one speak and not see them , they 'd think that they were real .