A new study provides a novel theory for how delusions arise and why they persist (Devinsky O. Delusional misidentifications and duplications: right brain lesions, left brain delusions. Neurology. Jan 2009;72:80-87). Orrin Devinsky, MD, a researcher at the New York University (NYU) Langone Medical Center, performed an in-depth analysis of patients with certain delusions and brain disorders and observed a consistent pattern of injury to the frontal lobe and right hemisphere of the brain.
The cognitive deficits caused by injuries to the right hemisphere lead to overcompensation by the left hemisphere, which results in delusions.
"Problems caused by these brain injuries include impairment in monitoring of self, awareness of errors, and incorrectly identifying what is familiar and what is a work of fiction," says Devinsky, professor of neurology, psychiatry and neurosurgery and director of the NYU Epilepsy Center. "However, delusions result from the loss of these functions, as well as the overactivation of the left hemisphere and its language structures, that 'create a story', a story which cannot be edited and modified to account for reality. Delusions result from right hemisphere lesions, but it is the left hemisphere that is deluded."
Delusions are pathologic beliefs that remain fixed, despite clear evidence that they're incorrect. "Delusions are common problems in a variety of psychiatric and neurological disorders," says Devinsky. Psychiatric disorders with delusions, such as schizophrenia, have been proven to have functional and structural brain pathology, he adds. But now, improved diagnostic techniques are allowing clinicians to be able to identify neurologic disorders among other patient populations with delusions.
In the study, most neurologic patients with delusions had lesions in the right hemisphere and bifrontal areas. For example, the neurologic disorders of confabulation, capgras and prosopagnosia result from right-sided lesions. Confabulation is incorrect or distorted statements that are made without conscious effort to deceive; capgras is the ability to consciously recognize familiar faces, but not emotionally connect with them; and with prosopagnosia, patients may fail to recognize spouses or their own face but generate an unconscious response to familiar faces.
The right hemisphere of the brain dominates self-recognition, emotional familiarity and ego boundaries. After injury, the left hemisphere tends to have a creative narrator that leads to excessive, false explanations. The resistance of delusions to change, despite clear evidence that they are wrong, likely reflects frontal dysfunction of the brain. This dysfunction impairs a person's ability to monitor himself and to recognize and correct inaccurate memories and familiarity assessments. Thus, right hemisphere lesions may cause delusions by disrupting the relationship between and the monitoring of psychic, emotional and physical self to people, places and body parts.
"Our knowledge of delusions is limited by our ability to comprehend the patient's irrational thought process," says Devinsky. "The pathogenesis of delusions likely includes many mechanisms that span overlapping psychological, cognitive and neurological disorders. Future research should explore the psychological, cognitive and pyschologic-anatomic systems that change during the emergence and resolution of delusions, as well as strategies to treat delusions."
Other studies have looked at delusions related to brain injuries. In one study, nine patients with right-hemisphere infarctions at a stroke rehabilitation unit had frequent delusion. While stroke size didn't correlate when compared with the control group, the presence of brain atrophy was a significant predictor of delusions. When delusions occurred, it was usually caused by a right-hemisphere lesion.
Other research has shown that reduplicative paramnesia and capgras syndrome cases with unilateral brain lesions implicate the right hemisphere, usually the frontal lobe of the brain. Among 69 patients with reduplicative paramnesia, lesions were primarily in the right hemisphere in 36 cases (52%), bilateral in 28 (41%) and left hemisphere in 5 (7%). Also, in 26 capras patients, lesions were primarily in the right hemisphere in 8 (32%), bilateral in 16 (62%) and left sided in 2 (7%). For both delusional syndromes, many bilaterial cases had maximal damage in the right hemisphere.
--Source: NYU Langone Medical Center
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