Prosopagnosia is defined as the inability to recognize known and new faces. It is also known as facial/visual agnosia. Bodamer first used the word prosopagnosia in 1947 in a landmark paper that described the cases of two patients with face recognition deficits. The word comes from Greek prosopon, meaning face and agnosia, meaning lack of knowledge. Normally, an individual can recognize and remember 5000+ faces throughout their lifetime.
There are varying degrees of impairment in prosopagnosia, including:
To compensate for their deficit, patients use their other senses and cues such as voice, shapes, and anomalous contours of the face. These compensatory mechanisms, at times, are not enough to recognize familiar faces. This impairment causes a psychological and social impact leading to functional impairment, unemployment, social isolation, depression, anxiety, and other mood disorders. Peculiarly, patients complain of having trouble following television shows and movies because they cannot visually keep track of characters.
Prosopagnosia can be acquired or hereditary. Acquired cases can resutl from ischemic or hemorrhagic stroke, traumatic brain injury, certain neurodegenerative and neuropsychiatric illnesses (Alzheimer disease, depression, and schizophrenia). Hereditary or development etiologies are a hot area of research, given that they are more common than acquired etiologies. The prevalence can approach 2.5% of the population. The mechanism of inheritance is not totally clear but thought to be autosomal dominant. Patients with juvenile prosopagnosia cannot recognize faces throughout their life, and a strong family history is usually present. It can be present in children with developmental disorders, including autism and Asperger syndrome. The impairment affects social development. Difficulties include lack of fear of strangers, intense separation anxiety, behavioral issues, and refusal to perform tasks that required face recognition.
Variants of prosopagnosia include an apperceptive variant (deficits in facial structure perception), and amnestic or associative variant (unable to remember faces even though they can perceive them; the perceptual information can not access facial memories because of a disconnection or loss of them).
The pathophysiology is still not completely understood and is a prominent area of research. Damage or developmental anomaly in the right or bilateral fusiform-lingual gyrus, with neuron pathways that control facial perception and memory, are thought to be involved. Imaging research shows that deficits in the temporal cortex and amygdala can also be involved. Individuals with fusiform lesions are more likely to have an apperceptive variant, while those with anterior temporal lobe lesions have the amnesia variant. Development prosopagnosia appears to be a result of either a disconnection between the anterior and posterior face networks or reduced functional activation of regions responsible for facial recognition and identification. Advanced imaging studies support these concepts. The hypothesis is that dysfunctional neural migration during development may be the mechanism behind juvenile prosopagnosia.
Neuropsychological Diagnostic Tests
Diagnostic tests can divide into three main types. First, perception tests that can accurately evaluate the patient's ability to discriminate between different visual facial stimuli. Second, recognition tests that can specifically assess short and long term recognition patterns of faces. Third, facial identification tests that involve other auditory or tactile cues (such as naming) to help identify facial stimuli. Examples for face perception tests are the Cambridge Face Perception Test, Glasgow Face Matching Test, Benton Facial Recognition, and the Caledonian Face Test.
Facial memories are testable through imagery. Other tools include self-report questionnaires, including the Cambridge Face Memory Questionnaire, Kennerknecht 15-item questionnaire, and the 20-item Prosopagnosia Index. These instruments of research tend to have low sensitivity and specificity for diagnosing prosopagnosia; therefore, objective measures should be pursued.
Advanced imaging is a research tool that uses properties such as cortical thickness, functional activation, and connectivity to study the networks involved in different types of prosopagnosia. Studies using positron-emission tomography scan and functional magnetic resonance imaging show that facial recognition networks are located in multiple brain regions, including the anterior temporal lobe, prefrontal cortex, inferior and middle temporal cortex, the hippocampus, the amygdala, and most importantly, and the fusiform face area or occipitotemporal gyrus. Activation of the fusiform face area in the non-dominant hemisphere appears to be involved in processing, while activation in the dominant hemisphere is associated with analytic processing. The perirhinal cortex in the medial temporal lobe is also involved in familiarity-based recognition. The different brain regions work synergistically to encode, store, and retrieve memories related to face recognition.
At this time, there is no evidence-based study that guides the creation of an interdisciplinary team for prosopagnosia. However, a neurologist, neuropsychologist, social worker, mental health counselor, psychiatrist, and geneticist should be consulted to provide the best care and quality of life for a patient with familial and acquired prosopagnosia. [Level ]
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