21 September 2006. Paranoia and the sense that others are controlling one’s thoughts and actions are prominent in many people with schizophrenia, but there is little understanding of what underlies these symptoms. A short case report in today’s issue of Nature offers a serendipitous clue about one brain region that may be involved. Olaf Blanke of the École Polytechnique Fédérale of Lausanne, Switzerland, and colleagues report that electrical stimulation at the junction between the temporal and parietal lobes in an awake patient evoked a sensation of a shadow person, who mirrored the patient’s movements.
First author Shahar Arzy and colleagues write that the 22-year-old woman was being evaluated for possible surgery to treat epilepsy when she reported a person mirroring her body position, but just outside it. At that moment, the researchers were stimulating in the border zone of the temporal and parietal lobes, an area that has been found to integrate sensory information to help create accurate perceptions of the body and self (see also Arzy et al., 2006).
When the patient sat up and embraced her knees, the shadow person seemed to embrace her, and it was not a pleasant experience. Even more interesting, when she sorted cards, the authors write, she reported the shadow person interfering with her: “He wants to take the card. He doesn’t want me to read.”
The authors note that Chloe Farrer of Institut des Sciences Cognitives in Lyon, France, and colleagues have linked hyperactivity in temporoparietal cortex with the misattribution of agency in patients with schizophrenia (Farrer et al., 2004). “Although our patient was aware of the similarity between her own postural and positional features and those of the illusory person, she did not recognize that that person was an illusion of her own body, like many deluded schizophrenic patients,” the authors write.—Hakon Heimer.
Arzy S, Seeck M, Ortigue S, Spinelli L, Blanke O. Induction of an illusory shadow person. Nature. 2006; Sep 21. Abstract