Prosopagnosia- A Room Full Of Strangers Everyday!

Moumita Ghosh, Amity University Kolkata

Introduction

Prosopagnosia is an impairment that causes the inability to acknowledge previously known faces and to find out new faces. It is also known as “face-blindness”. It may occur as a developmental variant or after a brain lesion. Humans have acquired the flexibility of recognizing faces effortlessly, rapidly, and accurately due to their social importance. It is estimated that a person can remember and recognize about 5000 faces. However, this may not be true for few people. Subjects with Prosopagnosia cannot identify a well-recognized face or any face recently encountered. They fail to spot people by their faces and thus communicate with other cues like voice, hairstyle, or anomalous facial features. This is not an issue of vision or memory or visual perception. These subjects realize faces but are unable to mention whether or not they have seen this person before or whose face is it.

Types

Prosopagnosia is of two types, acquired and developmental. In acquired Prosopagnosia, brain injury leads to poor face recognition. The first case of acquired Prosopagnosia was reported 150 years ago, impaired face recognition in wounded soldiers. It may also be caused due to various pathologies, stroke, trauma, encephalitis, degenerative atrophy, tumors, or lobe resections.  

Developmental Prosopagnosia has been more recently described and is still not well understood. Subjects with this condition despite having normal vision and memory fail to develop face recognition skills and do not have lesions on brain imaging. It might have a genetic basis that can run in families, with some pedigrees showing as many as ten affected members across two generations. The developmental form is more common than the acquired form which is quite rare. Some suggest that as many as 2.5% of the population has developmental Prosopagnosia.

Diagnosis

The most commonly used test is the Cambridge Face Memory Test (CFMT). This test incorporates high internal reliability. The first version of this test used only adult Caucasian faces but now other versions have also been created. CFMT uses anonymous faces so all subjects taking the test have the identical degree of short-term familiarity with the faces seen during the test as none of them are accustomed to the faces. Famous faces are also used for the test of familiarity, but these tests depend on the person if they have seen those celebrities before. Thus these tests are affected by different ages, education, and cultural background. Therefore these subjects cannot keep track of recent celebrities and characters and ultimately find a lack of interest in films and TV.

Diagnostic tests are of three main types: 

• The first is tests of face perception. This includes detecting different faces in arrays or comparing simultaneously seen faces; 
• The second is tests of face recognition. This includes tests for long-term and short term familiarity; 
• The third is tests of face identification and this includes giving the name or any other information related to the person shown.

Both recognition and identification are impaired in the cases of prosopagnosic subjects. Performing in these tests can help to differentiate between prosopagnosic subjects who have an apperceptive variant, within which there is an under-specification of a facial structure by perceptual processing, or an associative or amnestic variant, within which the person is unable to access facial memories. 

In diagnosing Prosopagnosia self-report questionnaires have become more common nowadays as they are effortless. Also, equipment is not required and need not be done in person thus can be accessed by an oversized number of subjects even at a distance. Among those are the Kennerknecht 15-item questionnaire, the 20-item Prosopagnosia Index, and also the Cambridge Face Memory Questionnaire. Reaching a firm diagnosis of developmental Prosopagnosia has its hurdles so screening for it should be possible with an easy list of 16 “hallmark symptoms” from experiences in day-to-day life, which can be reviewed by anyone.

Neuroimaging

The network of regions that are active during face perception includes a core face network that has the Fusiform face area (FFA), the occipital face area (OFA), and the posterior portion of the superior temporal sulcus. One more extended network that is a part of it is the anterior temporal face area and the inferior frontal gyrus and precuneus. These areas are activated in both hemispheres while face perception but the effect is stronger on the right.

The improved functional and structural capabilities of magnetic resonance imaging (MRI) have helped in studying prosopagnosia at an advanced level. When one considers the cosmopolitan network involved in face processing, a vital fact is that prosopagnosia can be caused by a range of lesions. From the study of acquired Prosopagnosia, one crucial observation is concluded that lesions could either be bilateral or unilateral, and in case of unilateral they are much more likely to be on the right. Some prosopagnosic subjects with left-sided lesions are described, but most are left-handed, raising the prospect that they may have had anomalous hemispheric lateralization to start with. 

Recent studies show that those with fusiform lesions are more likely to possess the apperceptive variant, whereas those with anterior temporal lesions are more likely to have the associative variant. The main conclusion is that acquired Prosopagnosia is not a single disorder, but a family of disorders with different mechanisms and different lesions that ultimately leads to the identical outcome of impaired face recognition.

The structural correlation of developmental Prosopagnosia is still not cleared. There are no obvious structural lesions. Abnormal activation of the core face network when studied and examined has produced mixed results- some reporting normal activation and the other one reporting activation for faces which was not different from activation for other object types. With the help of advanced imaging methods both structural and functional anomalies in developmental Prosopagnosia have begun to unveil, but again there are differences in arguments. Some recommended that there are anatomical or functional abnormalities within the FFA and localized differences in the substantia alba around the right FFA. While others believe that the core face network is normal and that abnormalities lie in the anterior temporal cortex, other regions of the extended face network, or the white matter tracts which is a connection for the core regions in the occipitotemporal cortex to the anterior temporal face area, and the inferior longitudinal fasciculus. Both groups claim that the grade of altered white matter connectivity in their results corresponded to behavioral measures of impaired face recognition. It is yet to be determined if these discrepancies in the least reflect a real heterogeneity that exists in developmental Prosopagnosia.

Treatment:

Spontaneous resolution of acquired Prosopagnosia is rare and developmental Prosopagnosia is a lifelong disorder. Thus it is the clinical interest of that population that may improve the face recognition skills. But can it be done? It is seen during the process of neuroimaging that regions of both hemispheres like occipitotemporal, superior temporal, anterior temporal, and inferior frontal regions are activated during face processing. Now the question is whether or not a selected prosopagnosic subject will have the capacity to improve the face recognition ability through functional reorganization or modulation by the assistance of a rehabilitative approach.

A fascinating report of transient improvement of developmental Prosopagnosia includes the intranasal inhalation of oxytocin. Compensatory strategies have been taken which aim to achieve a person’s recognition by circumventing the face processing impairment and remediation, this aims to boost that impairment. Numerous advances have been seen in trials of perceptual learning in groups over single cases of prosopagnosia. In one such study of 24 subjects with developmental Prosopagnosia, over 2 weeks, subjects learned to discriminate the distances between the facial expressions. These “spatial relations” act as indices of the complex geometry of faces. This trial found improved face perception but with a limitation that as long as the test faces had an analogous frontal view and if encountered regular faces. 

10 subjects with acquired prosopagnosia were used for the second study where morphed faces were used to train subjects for 11 weeks to perceive finer and finer differences in facial shape. Simultaneously, irrelevant variations in the expression and viewpoint of the face were introduced in the study. These subjects showed a 21% absolute increase in perceptual sensitivity to facial shape after training, which generalized over new views and expressions compared with a sway condition. These subjects showed improvement in not only learning the identical faces but could also perceive new faces. 

Conclusion:

Even though these rehabilitative studies and training methods represent a start line, they do not represent a “cure”. They supply evidence that face processing can be changed in prosopagnosia and there could also be individual differences in training potential. There is yet enough work to be done to know if better learning and training with the employment of additional techniques helps in perceptual gain.  

Also read: Novel brain cells named “Gorditas” and “OPC” discovered

References:

1. Corrow, S. L., Dalrymple, K. A., & Barton, J. J. (2016). Prosopagnosia: current perspectives. Eye and brain, 8, 165.https://doi.org/10.12688/f1000research.18492.1

2. Della Sala, S., & Young, A. W. (2003). Quaglino’s 1867 case of prosopagnosia. Cortex, 39(3), 533-540.https://doi.org/10.2147/EB.S92838

3. Jenkins, R., Dowsett, A. J., & Burton, A. M. (2018). How many faces do people know?. Proceedings of the Royal Society B, 285(1888), 20181319. https://doi.org/10.1098/rspb.2018.1319

4. Quaglino, A., & Borelli, G. (1867). Emiplegia sinistra con amaurosi–guarigione–perdita totale della percezione dei colori e della memoria della configurazione degli oggetti. Giornale d’Oftalmologia Italiano, 10, 106-117. http://dx.doi.org/10.1016/j.neuroimage.2007.10.047

5. Yardley, L., McDermott, L., Pisarski, S., Duchaine, B., & Nakayama, K. (2008). Psychosocial consequences of developmental prosopagnosia: A problem of recognition. Journal of psychosomatic research, 65(5), 445-451. https://doi.org/10.1016/j.jpsychores.2008.03.013

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