A Neurological Basis for Psychiatric Delusions

Candice Davidoff
University of Pennsylvania

A group led by Dr. Shahar Arzy has serendipitously found a potential neurological basis for severe psychiatric symptoms including own-body perceptions, paranoia, and delusions of alien control.

Their patient, a 22-year-old woman with a normal psychiatric history, was being evaluated for surgery for epilepsy by application of a 10mA current to various brain regions [1]. During the test, focal electric stimulation was applied to a part of the brain called the temporoparietal junction. The pulse induced an eerie sensation that another person was in the room when no one else was present. The woman described the illusory person as a silent and unmoving “shadow”, young and of indeterminate sex, and whose position in space was identical to her own [1]. When she changed positions and the current was reapplied, the shadow had changed positions to match hers. She reported discomfort at the shadow’s proximity and claimed that it was trying to interefere with her activities [1,2]. The illusion disappeared when the stimulation was terminated [1].

The group hypothesized that the false perceptions resulted from a disturbance in the multisensory processing of body and self at the temporoparietal junction [1]. This region is known to be involved in self-processing and self-other distinction [3]. The electrical stimulation may have disrupted the proprioceptive and sensorimotor integration that normally occurs at the temporoparietal junction, causing a manifestation of first-order psychiatric symptoms. Essentially, the strange sensations were a misinterpretation of sensory information about the patient herself [1,2].

This finding could provide the neurological basis for the delusions often experienced in patients with schizophrenia and other psychiatric disorders. If future research confirms that these patients indeed have aberrant activity in the temporoparietal junction, a better understanding of how this region functions could eventually lead more effective treatments for people suffering from such diseases.

References:

[1] Arzy, S. et al. “Induction of an illusory shadow person.” Nature. 443, 287(21 September 2006).

[2] Blakeslee, Sandra. “Out of Body Experience? Your Brain is to Blame” New York Times. 3 October 2006.

[3] Ruby, P. & Decety. “Effect of subjective perspective taking during simulation of action: a PET investigation of agency.” Journal of Nature, Neuroscience. 4, 546–550 (2001).

Image courtesy of intramural.nimh.nih.gov.