A Neurological Basis for Psychiatric Delusions
11/01/06

Candice Davidoff
University of Pennsylvania

A group lead 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.

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