Summary: New research maps the brain networks linked to delusional misidentification syndromes, clarifying why patients may falsely perceive people or places as unfamiliar or impostors.
Source: BIDMC
Researchers identify brain networks associated with delusional misidentification syndromes
Neuroscientists at Beth Israel Deaconess Medical Center (BIDMC) have identified the brain regions and networks most commonly associated with delusional misidentification syndromes (DMS), a set of rare and striking disorders in which patients are convinced that people, animals or places are not what they appear to be. The findings, published in the journal Brain, are led by Michael D. Fox, MD, PhD, Director of the Laboratory for Brain Network Imaging and Modulation and Associate Director of the Berenson-Allen Center for Noninvasive Brain Stimulation at BIDMC, together with colleagues who used lesion network mapping to reveal the neuroanatomical basis of these delusions.
“Understanding how complex psychiatric and neurological symptoms arise from brain injury has been a longstanding challenge,” Fox said. “Our work shows that distinct symptoms can arise when a lesion disrupts the connections of brain regions responsible for familiarity and belief evaluation. When those networks are affected together, a patient can develop the bizarre misidentification beliefs seen in syndromes such as Capgras.”
Delusional misidentification syndromes have long fascinated clinicians. Capgras syndrome, first reported nearly a century ago, involves the patient recognizing a familiar person while simultaneously feeling that person is an impostor. The Fregoli delusion is the opposite: the belief that strangers are actually familiar people disguised as others. These delusions can also apply to pets, objects or the patient’s home, producing distressing and often bewildering behaviors.
In the study, lead author R. Ryan Darby, MD, and colleagues identified 17 patients with documented delusional misidentification syndromes and mapped the locations of their brain lesions onto a standardized brain atlas. Using lesion network mapping — a technique that determines which brain regions are functionally connected to a given lesion site based on normative brain connectivity data — the team found a common pattern. All 17 lesion locations were functionally connected to the retrosplenial cortex, a brain area implicated in the experience of familiarity. Sixteen of the 17 lesions were also connected to a region in the right ventral frontal cortex, a region linked to belief evaluation and monitoring.
To distinguish networks specific to misidentification from those linked to delusions in general, the researchers compared the DMS lesion network data to a control group of 15 lesions that caused other types of delusions. The comparison suggested that belief-evaluation regions are involved broadly in delusional states, whereas the additional involvement of familiarity-processing regions appears to explain the characteristic content of misidentification delusions: abnormal feelings of familiarity or unfamiliarity about known people, places or objects.
“Lesions that lead to delusions in general tend to impact brain areas involved in detecting belief violations, which may underlie the formation or persistence of false beliefs,” Darby said. “But only lesions connected to familiarity-processing regions produced the particular sensation that someone known is somehow not real. In cases like Capgras, a lesion’s connections to both types of regions appear necessary for the full syndrome to develop.”
The authors note that lesion network mapping relies on connectivity data from healthy individuals to infer which regions are normally connected to a lesion site; it does not require functional MRI from each patient with the disorder. This approach has advantages for studying rare syndromes, but it does not by itself prove that the retrosplenial or right ventral frontal regions become dysfunctional in every patient after injury. Confirming dysfunction in those regions would require prospective functional imaging or larger cohorts of patients with these rare conditions.
Beyond the scientific implications, the findings may have practical value for families and clinicians. Misidentification delusions can cause profound distress: some patients repeatedly attempt to return to what they believe is their “real” home, while others withdraw from spouses they mistakenly label as impostors. Knowing that these experiences have identifiable neuroanatomical correlates can provide relief and guide care strategies for affected families.
Study coauthors include Simon Laganiere, MD, and Alvaro Pascual-Leone, MD, PhD, of the Berenson-Allen Center for Noninvasive Brain Stimulation at BIDMC, and Sashank Prasad, MD, of the Department of Neurology at Brigham and Women’s Hospital.
Funding: Support for this work came from the Sidney R. Baer, Jr. Foundation; multiple National Institutes of Health grants (including R01 and R21 mechanisms); the Football Players Health Study at Harvard University; Harvard Catalyst | The Harvard Clinical and Translational Science Center; and the American Brain Foundation.
Source: Jacqueline Mitchell, BIDMC
Original Research: The study appears in the journal Brain.
BIDMC. “The Man Who Mistook His Wife For An Imposter.” NeuroscienceNews. 20 December 2016.