Like schizophrenics, the patient did not recognize that she was experiencing an illusion of her own body.
"In that condition she might have understood that [the shadow] was an illusion, but she didn't," said study co-author Stephanie Ortigue, a neuroscientist at Dartmouth College in Hanover, New Hampshire.
Disturbed Sense of Self
Researchers suggest that the electrical stimuli may have disturbed the brain's concept of its own body.
The brain's temporoparietal junction has been linked to self-perception and the processes that distinguish oneself from others.
The region helps humans understand their spatial environment as well as their bodies' positions in that environment.
"It's an area that is known to be involved in the integration of different modalities like visual, auditory, tactileall the modalities that make you realize where your body is in space and what you feel," Ortigue said.
Hyperactivity in the region has been found in schizophrenics who attribute their own actions to other people.
(See National Geographic magazine's "Beyond the Brain.")
Idil Cavus, a professor of psychiatry at Yale University School of Medicine, found the report interesting and promising, but she offered a caveat.
"This is only one subject," Cavus said.
"So the question is whether this is something that can be obtained in other patients or whether it was somehow particular to that patient because [of her epileptic condition]."
Cavus also notes that schizophrenia is a far more complicated condition than that exhibited by the study's female subject. The perception of shadow people is reminicent of, but not necessarily the same as, a host of delusions suffered by schizophrenics.
"They report seeing and hearing things that can be anywhere around [them]," Cavus explained.
"[Delusions] can be sounds or visions of people. Many times it's a sense of being watched, of being tracked, of being talked to.
"People can have very complex delusions about alien control or having things implanted in their brains, or about others watching them, controlling their thoughts, and telling them what to do," she continued.
Schizophrenia affects about one out of every hundred people worldwide.
The recent find could help scientists unravel the brain processes behind such debilitating mental illnesses.
"We understand so little about how the brain makes sense of itself," Cavus said.
"It's very interesting to pursue how those processes can be broken down."
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