What is Prosopagnosia?

By Chris Gabriel

When you think of the person you love most in the world, you might imagine their face, their voice, and the memories you’ve shared together. Now, imagine seeing a photo of that person and, despite the strength of the bond you share, being completely unable to recognize them. This is the reality for people who have “face blindness”, also known as prosopagnosia. Unable to recognize the faces of strangers and loved ones alike, if you have prosopagnosia you may even struggle to recognize yourself in the mirror.

Prosopagnosia is a neurological condition characterized by the inability to recognize familiar faces. You may never have heard of prosopagnosia, but it affects 1-3% of the population, and a recent study suggests that many cases go undiagnosed due to rigid diagnostic criteria (DeGutis et al., 2023). Instead of being a skill you have or don’t, facial recognition exists on a spectrum. Individuals may fail to distinguish faces from other objects, struggle to identify faces they are looking at, or even have the capacity for ‘super’ recognition, an enhanced ability to distinguish faces relative to an average person (Bate et al., 2021). Given their difficulty with recognizing familiar individuals, prosopagnosia patients frequently report having traumatic social experiences, chronic anxiety, and feelings of embarrassment and guilt as a result of their symptoms (Dalrymple et al., 2014; Corrow et al., 2016). Writing about her experiences with prosopagnosia, Sadie Dingfelder described interacting for months with two coworkers she believed were the same person and joking with her husband at the store, only to realize it was a complete stranger with a similar jacket (Dingfelder, 2019). The ability to recognize the faces of people you know is a signal that they are important to you. As such, patients with this disorder can struggle to find and maintain employment and can withdraw from social situations, fearing an awkward explanation for why they can’t recognize someone they know.

The cause of prosopagnosia varies depending on whether you were born with it or developed it. Developmental (or congenital) prosopagnosia is a lifelong disorder with unknown causes that might arise from abnormal development in the brain regions in charge of processing faces (Albonico & Barton, 2019). Though we don’t know how this abnormal development occurs, there is reason to believe genetics are involved—you are more likely to have prosopagnosia if it runs in your family, and facial recognition abilities tend to be more similar among family members than between members of the general public (Zhu et al., 2010). Researchers have proposed two main theories to explain how this disorder occurs. One theory suggests that alterations in brain regions important for processing faces lead to disrupted face recognition (Dinkelacker et al., 2011; Lohse et al., 2016). A second theory posits that face processing areas in the front and back of the brain can become disconnected, and this lack of communication between these areas drives face blindness (Rosenthal et al., 2017). Both theories are based on observations and evidence from patients, but it remains unclear if either (or both) are correct.

Acquired prosopagnosia occurs when a brain injury damages part of the face processing network, resulting in issues with face perception and recognition. These injuries, such as a brain lesion or stroke, disrupt the face perception network and cause different symptoms based on the location and severity of the injury. Acquired prosopagnosia can be especially useful to study, as patients tend to have normal face perception before onset, and the focal nature of these injuries allows researchers to study more precisely how brain activity has changed. Observations from patients with acquired prosopagnosia have shown that face blindness is associated with lesions of the right hemisphere and rarely occurs after lesions of the left hemisphere (Damasio et al., 1982; Landis et al., 1986). Patients with acquired prosopagnosia also tend to have injuries in two main regions: the ventral occipito-temporal/fusiform cortices and the anterior temporal cortex. These injuries can be in one region or the other but can also be in both. Those with occipito-temporal/fusiform lesions tend to have apperceptive prosopagnosia, defined by a complete inability to distinguish faces from non-faces (Barton et al., 2002). Patients with lesions of the anterior temporal cortex tend to have amnestic prosopagnosia, characterized by better perceptual function and the ability to distinguish faces from other objects but inability to identify people from their faces (Barton, 2008).

The nature of prosopagnosia provides unique insights into the way the brain has evolved to support the social lifestyle of humans. The most intuitive explanations for prosopagnosia—that it is caused by a deficit in general vision or memory—have not been supported by research (National Institute of Neurological Disorders & Stroke). At first believing that face blindness would affect object recognition in general, researchers were surprised to find evidence of problems in systems specifically dedicated to processing facial information. Thus, studying prosopagnosia allows researchers to examine how humans recognize objects more broadly. Does the brain have a highly specific system for facial recognition? Or does the ability to recognize faces come from the refinement of general object recognition systems? Our current evaluation of prosopagnosia patients suggests that most, but not all, have some impairment on other object recognition tests (Geskin & Behrmann, 2018). This supports the idea that facial recognition occurs in a distributed network that processes faces alongside other objects. However, more research must be done to fully understand how entangled facial recognition is with other types of objects, particularly given the existence of patients with no additional object recognition deficits.

Unfortunately, there is currently no cure for prosopagnosia. However, patients are often able to compensate for their face blindness by relying on other cues (e.g. haircut style, the sound of a particular voice). Currently, several treatments are aimed at strengthening face recognition in patients with prosopagnosia. These either train a patient’s perception of facial features (e.g. learning to notice the distance between facial features) or develop strategies to enhance the memory of faces, such as the use of mnemonics (Bate & Bennetts, 2014; Davies-Thompson et al., 2017). Though these interventions have had mild success, more research is needed in order to find a cure.

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Written by Chris Gabriel

Illustrated by Federica Raguseo

Edited by Zoe Dobler, Johanna Popp, Shiri Spitz Siddiqi

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References
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