By Claire Deckers
Imagine looking in the mirror and not recognizing the face looking back at you, or trying to find a close friend, but not identifying them even when they were right in front of you. These symptoms are consistent with a psychological disorder known as prosopagnosia, commonly referred to as “face blindness”. People with this disorder have trouble recognizing faces, even those of friends, family, and themselves. It is estimated that around 2% of the population, or 1 in fifty people, experiences some sort of prosopagnosia, despite there being just 100 documented cases of the disorder worldwide (Chowhan, 2013). This discrepancy is due to the general difficulty in diagnosing the disorder.
Those who are born with the disorder often develop coping mechanisms that allow them to continue with everyday life without seeking psychological or medical intervention. More uncommonly, others experience an onset of prosopagnosia following a stroke or acute brain damage, in which the disorder may be overlooked in favor of addressing other symptoms associated with neurological injury.
Those with prosopagnosia experience this impaired ability to recognize faces, despite having normal visual processing abilities. Although this non-recognition will obviously have a major impact on an individual’s life, as mentioned earlier, many develop coping strategies that allow them to live a normal life. Common strategies include memorization of non-facial qualities, including hairstyle, voice, or gait. Additionally, those with prosopagnosia often report feeling an unconscious recognition when seeing the face of someone they know, despite not being able to identify them.
In a disorder sometimes referred to as the “inverse” of prosopagnosia, Capgras Syndrome, patients are able to recognize faces of loved ones, but believe that they have been replaced by an imposter who is trying to cause them harm. These delusions are unshakable—even if those with Capgras Syndrome are able to recognize these feelings are irrational, they will find ways to generate explanations for how this replacement has taken place. Capgras Syndrome is slightly more uncommon, with an overall prevalence of 1.3% (Tamam, 2003). It is often reported occurring in the context of schizophrenia or cerebrovascular diseases such as dementia or epilepsy. However, interestingly, and very rarely, some patients are not able to be identified with any other sort of preceding psychological dysfunction. In these cases, researchers believe that the presence of Capgras symptoms is due to some sort of underlying biological factor that has not yet been fully elucidated.
The description of prosopagnosia and Capgras Syndrome as “inverse” disorders is apt, and can be seen within physiological testing. One distinguishing test that is often performed is the skin conductance response, or SCR. Within SCR testing, electrodes that record electric conductance in the skin are placed on the fingers. When individuals experience stimuli that elicit a physiological response, like a frightening picture or, in this case, the face of someone they know, electric conductance is briefly increased by activation of the sympathetic nervous system (i.e. your “fight or flight” response). When patients with prosopagnosia undergo SCR testing while viewing familiar faces, their response will actually be completely intact. This means that even though they do not display conscious facial recognition, they are still able to recognize them on a physiological level (perhaps contributing to the “feeling of familiarity” these individuals report). In contrast, those with Capgras, who do display conscious facial recognition, elevated SCR response is completely absent in the presence of images of friends and family (Brighetti, 2006). Although they know the individuals that these faces belong to, on some level, they do not actually believe that it is that person.
On a neurological level, researchers believe that these differences emerge because of variations in brain dysfunction. In prosopagnosia, inability to recognize faces is thought to stem from damage within the ventral visual pathway, which is responsible for object identification. The dorsal visual pathway, responsible for spatial vision and related behaviors, is unaffected, leading to the correspondingly unaffected visual acuity in these individuals. Conversely, in Capgras patients, it is hypothesized that perhaps symptoms are due to damage within the dorsal stream, further evidencing the inverse nature of the two disorders (Edelstyn, 1999). Additionally, damage within the ventral limbic structure, which is associated with emotional processing of input from sensory systems is often present in these patients (Haxby, 2001).
Emerging data suggests an additional potential mechanism for Capgras. In Horikawa, et al. (2006), researchers examined the brain of a patient who struggled with recurring episodes of Capgras using a technique called “single-photon emission computed tomography” (SPECT). SPECT is a type of brain scan that allows researchers to visualize how blood flows through the vasculature throughout the brain.
SPECT Imaging Results in Capgras Syndrome: Horikawa, et al. (2006). Figure 1. Different SPECT findings
before and after Capgras’ syndrome in interictal psychosis. Epilepsy and Behavior, Vol 9(1): 189-192. DOI: 10.1016/j.yebeh.2006.04.016
In the image above, three different incidences of the patient’s Capgras delusions are shown, with the pre-onset brain image viewed by the side labeled “L”. As you move towards the left in each row, the patient’s brain image during a delusional event, and finally moving into the post-event brain image on the side labeled “R”. The images demonstrate an increased amount of hypoperfusion, or increased blood flow (seen in the darkening of shading), particularly on the right side of the brain. From this, the researchers suggest an additional mechanism for the presence of Capgras, in which dysfunction within this right brain lobe contributes to the disconnect between recognition and belief in that recognition.
Although these potential mechanisms for both prosopagnosia and Capgras have been suggested, due to the relative rarity of the disorders, as well as the limited research into neurobiological basis, researchers are not entirely sure about the exact reason for the presence of these disorders. In either case, these disorders affect parts of human experience and life that most of us take for granted, and thus warrant further exploration and understanding.
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