Mirrored-self misidentification
Mirrored-self misidentification is the delusional belief that one's reflection in the mirror is another person – typically a younger or second version of one's self, a stranger, or a relative. This delusion occurs most frequently in patients with dementia and an affected patient maintains the ability to recognize others' reflections in the mirror. It is caused by right hemisphere cranial dysfunction that results from traumatic brain injury, stroke, or general neurological illness. It is an example of a monothematic delusion, a condition in which all abnormal beliefs have one common theme, as opposed to a polythematic delusion, in which a variety of unrelated delusional beliefs exist. This delusion is also classified as one of the delusional misidentification syndromes. A patient with a DMS condition consistently misidentifies places, objects, persons, or events. DMS patients are not aware of their psychological condition, are resistant to correction and their conditions are associated with brain disease – particularly right hemisphere brain damage and dysfunction.
Prevalence
Delusional misidentification syndromes can occur in patients with a wide variety of cranial dysfunctions. Mirrored-self misidentification, a type of DMS, occurs most typically in patients with dementia, especially Alzheimer's disease. Approximately 2% to 10% of all patients with Alzheimer's disease have mirrored-self misidentification. Patients with schizophrenia, right frontal ischemic stroke, and rarely patients with Parkinson's disease have also reported being affected by this delusion. The exact prevalence of patients with this delusion is relatively unknown because the typical patient has many comorbidities; this makes it difficult to separate the symptoms of mirrored-self misidentification from other existing psychological conditions. Furthermore, a standard neurological or neuropsychological workup tends to overlook the existence of this delusion because affected patients have extensive cognitive degeneration that is the main focus of medical attention. As such, it can be incumbent upon the patient's family to recognize symptoms of the delusion, mainly that the patient is unable to recognize him or herself in the mirror but has an intact ability to recognize the reflections of others.Neurological basis
All patients with mirrored-self misidentification have some type of right hemisphere dysfunction. The right hemisphere, particularly frontal right hemisphere circuits, is involved in processing self-related stimuli and helps one recognize a picture or reflection of oneself. An impairment in the right hemisphere, the likely source of the "self" in the brain, can inhibit one's ability to recognize faces, especially one's own.Patients tend to experience a distortion of the right dorsolateral prefrontal cortex, which impairs the patient's belief evaluation system. Patients can no longer logically reject delusional beliefs. Injury to the right frontal lobe is found in 35% of cases and can also inhibit one's ability to reject delusional beliefs on the basis of implausibility. Patients with this delusion also tend to have larger right anterior horns than the typical person. These cranial distortions point to right frontal atrophy and general right hemisphere dysfunction.
While approximately 50% of all patients exhibit left hemisphere damage, all patients with this hemispheric dysfunction also have cranial lesions in the right hemisphere. As no patients with solely left hemisphere damage have been reported to experience this delusion, this points to the delusion being strongly associated with right hemisphere dysfunction.
In a few select case studies, patients with this delusion have such extensive right-hemisphere cranial damage that one is also unable to identify close relatives and others with whom the patient has close association. Such extensive damage in mirrored-self misidentification patients is rare; typically patients retain the ability to recognize others’ reflections in the mirror. When such extensive neurological damage occurs, the affected patient relies on non-facial cues to identify relatives. When looking in a mirror, the patient can only use facial cues to recognize one self. Therefore, in these rare cases, despite damage to the entire facial recognition area of the brain, the patient is still able to recognize relatives but unable to recognize the self in the mirror.
Famous studies
There are two famous case studies of patients with mirrored-self misidentification that have contributed to the overall understanding of this delusion.Case one: patient TH
Patient TH was in the early stages of dementia and was affected by mirror agnosia. While TH was looking into a mirror, the researcher held an object behind TH in such a way so it was reflected in the mirror. Due to his belief that mirrors represent a separate place, TH tried to reach into the mirror to retrieve the object rather than reaching over his shoulder. TH's mirror agnosia accounts for the development of the delusional idea. Because not all patients with mirror agnosia develop the delusion, there needs to be the presence of a second factor that explains why TH does not reject his delusional belief that the object is inside the mirror. Neuropsychological testing showed TH had an impaired right hemisphere. He displayed poor visual memory and visuoconstructional problems but still had basic visuoperceptual skills, a normal intelligence, typical vocabulary, and average semantic ability. These issues are indicative of significant right hemisphere dysfunction, specifically in the right dorsolateral prefrontal cortex. Because of such cranial impairments, TH was unable to use logic to reject his delusional beliefs based on implausibility. From this case study, researchers concluded that while not all patients with mirror agnosia develop mirrored-self misidentification, when mirror agnosia is paired with right hemisphere damage of the belief evaluation system, the delusion will develop.Case two: patient FE
Patient FE was also in early stages of dementia but experienced impaired facial processing rather than mirror agnosia. His distorted perception of his reflection in the mirror made him unable to pair the reflection to a memory of the appearance of his own face. This prompted him to believe that the person in the mirror was someone other than himself. Because not all patients with impaired facial processing develop mirrored-self misidentification, such as patients with prosopagnosia, there needed to be a second factor to explain FE's delusions. Neuropsychological testing showed that FE had extensive cranial damage in his right hemisphere. He had poor visual memory and visuoconstructional problems whilst retaining basic visuoperceptual skills. These impairments made FE unable to use logic to reject his belief that the person in the mirror was someone other than him. From this case study, researchers concluded that while not all patients with impaired facial processing develop mirrored-self misidentification, when the impairment is paired with damage to the belief evaluation system in the right dorsolateral prefrontal cortex, the delusion will develop.Two-factor theory of delusional belief
Mirrored-self misidentification is an example of a monothematic delusion – a delusion restricted to a single topic or theme. The two-factor theory of delusional belief explains why monothematic delusions occur. The two case studies outlined above helped with the development of this theory. The theory states that two separate factors are together responsible for monothematic delusions. The first factor explains the content of the delusion and strives to determine why the delusional idea developed. The second factor identifies why the delusion persists rather than being rejected based on implausibility or bizarreness.Factor 1
Factor 1 is responsible for identifying why the delusional idea developed. In monothematic delusions, some neuropsychological abnormality typically causes the delusion. In mirrored-self misidentification, this abnormality can be either impaired facial processing or mirror agnosia. Patients with impaired facial processing cannot pair the reflected face in the mirror to a memory of one's own face, thus leading to the conclusion that the person in the mirror must be someone other than one's self. Patients with mirror agnosia are unable to understand how mirrors work; they believe the mirror represents a separate space, typically either the other side of a window or another room due to the presence of a hole in the wall. However, not all patients with impaired facial processing or mirror agnosia develop the delusion; there therefore needs to be a second factor that accounts for why some patients with impaired facial processing or mirror agnosia develop the delusion and others with the same conditions do not.Factor 2
Factor 2 is responsible for identifying why the delusion is an accepted belief rather than rejected due to implausibility or bizarreness. Damage to the right hemisphere, specifically the right dorsolateral prefrontal cortex, impairs the patient's belief evaluation system. The patient loses the ability to use logic to reject the delusional belief that the mirrored reflection is another person.Only patients who have both factor 1 and factor 2 will develop the mirrored-self misidentification delusion. Patients with impaired facial processing who do not have mirrored-self misidentification have prosopagnosia. Patients who experience right hemisphere dysfunction but do not have impaired facial processing or mirror agnosia will experience general sensory-motor and cognitive impairment.