What is prosopagnosia?

Prosopagnosia (also known as face blindness or facial agnosia) is a neurological disorder characterized by the inability to recognize faces. The term comes from the Greek words for “face” and “lack of knowledge.”

Depending upon the degree of impairment, some people with prosopagnosia may only have difficulty recognizing familiar faces, while others will be unable to discriminate between unknown faces. Other people may not be able to distinguish a face as being different from an object. Some people are unable to recognize their own faces. 

Prosopagnosia is not related to memory dysfunction, memory loss, impaired vision, or learning disabilities. The disorder is thought to be the result of congenital influence, damage, or impairment in a fold in the brain that appears to coordinate the neural systems controlling facial perception and memory (right fusiform gyrus). 

Prosopagnosia can result from stroke, traumatic brain injury (TBI), or certain neurodegenerative diseases. Some cases are congenital or present at birth, in the absence of any brain damage. Congenital prosopagnosia appears to run in families, which makes it likely to be the result of a genetic mutation or deletion. Some degree of prosopagnosia is often present in children with autism and Asperger's syndrome and may be the cause of impaired social development.

Treatment is aimed at helping individuals develop ways to compensate. Adults who have the condition as a result of stroke or brain trauma can be retrained to use other clues to identify individuals.

Prosopagnosia can be socially debilitating as individuals with the disorder often have difficulty recognizing family members and close friends. They often use other ways to identify people, such as relying on voice, clothing, or unique physical attributes.

How can I or my loved one help improve care for people with prosopagnosia?

Consider participating in a clinical trial so clinicians and scientists can learn more about prosopagnosia and related disorders. Clinical research uses human volunteers to help researchers learn more about a disorder and perhaps find better ways to safely detect, treat, or prevent disease.

All types of volunteers are needed—those who are healthy or may have an illness or disease—of all different ages, sexes, races, and ethnicities to ensure that study results apply to as many people as possible, and that treatments will be safe and effective for everyone who will use them.

A hereditary form of prosopagnosia, or inability to recognize someone by face alone in the absence of sensory or intellectual impairment. It appears to exhibit autosomal dominant inheritance and may affect 0.75-2% of different populations. 

Agnosia has been found to have many causes. For several types of agnosia, including prosopagnosia (an inability to recognize faces) and color agnosia, articles in the medical literature describe families in which multiple relatives have similar symptoms. The authors of these articles suggest this is evidence of a genetic factor contributing to agnosia in these families. However, a specific gene has not yet been found to cause this condition.

Cortical Processing

As described earlier, many of the sensory axons are positioned in the same way as their corresponding receptor cells in the body. This allows identification of the position of a stimulus on the basis of which receptor cells are sending information. The cerebral cortex also maintains this sensory topography in the particular areas of the cortex that correspond to the position of the receptor cells. The somatosensory cortex provides an example in which, in essence, the locations of the somatosensory receptors in the body are mapped onto the somatosensory cortex. This mapping is often depicted using a sensory homunculus (image).

The term homunculus comes from the Latin word for “little man” and refers to a map of the human body that is laid across a portion of the cerebral cortex. In the somatosensory cortex, the external genitals, feet, and lower legs are represented on the medial face of the gyrus within the longitudinal fissure. As the gyrus curves out of the fissure and along the surface of the parietal lobe, the body map continues through the thighs, hips, trunk, shoulders, arms, and hands. The head and face are just lateral to the fingers as the gyrus approaches the lateral sulcus. The representation of the body in this topographical map is medial to lateral from the lower to upper body. It is a continuation of the topographical arrangement seen in the dorsal column system, where axons from the lower body are carried in the fasciculus gracilis, whereas axons from the upper body are carried in the fasciculus cuneatus. As the dorsal column system continues into the medial lemniscus, these relationships are maintained. Also, the head and neck axons running from the trigeminal nuclei to the thalamus run adjacent to the upper body fibers. The connections through the thalamus maintain topography such that the anatomic information is preserved. Note that this correspondence does not result in a perfectly miniature scale version of the body, but rather exaggerates the more sensitive areas of the body, such as the fingers and lower face. Less sensitive areas of the body, such as the shoulders and back, are mapped to smaller areas on the cortex.

Likewise, the topographic relationship between the retina and the visual cortex is maintained throughout the visual pathway. The visual field is projected onto the two retinae, as described above, with sorting at the optic chiasm. The right peripheral visual field falls on the medial portion of the right retina and the lateral portion of the left retina. The right medial retina then projects across the midline through the optic chiasm. This results in the right visual field being processed in the left visual cortex. Likewise, the left visual field is processed in the right visual cortex (see image). Though the chiasm is helping to sort right and left visual information, superior and inferior visual information is maintained topographically in the visual pathway. Light from the superior visual field falls on the inferior retina, and light from the inferior visual field falls on the superior retina. This topography is maintained such that the superior region of the visual cortex processes the inferior visual field and vice versa. Therefore, the visual field information is inverted and reversed as it enters the visual cortex—up is down, and left is right. However, the cortex processes the visual information such that the final conscious perception of the visual field is correct. The topographic relationship is evident in that information from the foveal region of the retina is processed in the center of the primary visual cortex. Information from the peripheral regions of the retina are correspondingly processed toward the edges of the visual cortex. Similar to the exaggerations in the sensory homunculus of the somatosensory cortex, the foveal-processing area of the visual cortex is disproportionately larger than the areas processing peripheral vision.

In an experiment performed in the 1960s, subjects wore prism glasses so that the visual field was inverted before reaching the eye. On the first day of the experiment, subjects would duck when walking up to a table, thinking it was suspended from the ceiling. However, after a few days of acclimation, the subjects behaved as if everything were represented correctly. Therefore, the visual cortex is somewhat flexible in adapting to the information it receives from our eyes (image).

The cortex has been described as having specific regions that are responsible for processing specific information; there is the visual cortex, somatosensory cortex, gustatory cortex, etc. However, our experience of these senses is not divided. Instead, we experience what can be referred to as a seamless percept. Our perceptions of the various sensory modalities—though distinct in their content—are integrated by the brain so that we experience the world as a continuous whole.

In the cerebral cortex, sensory processing begins at the primary sensory cortex, then proceeds to an association area, and finally, into a multimodal integration area. For example, the visual pathway projects from the retinae through the thalamus to the primary visual cortex in the occipital lobe. This area is primarily in the medial wall within the longitudinal fissure. Here, visual stimuli begin to be recognized as basic shapes. Edges of objects are recognized and built into more complex shapes. Also, inputs from both eyes are compared to extract depth information. Because of the overlapping field of view between the two eyes, the brain can begin to estimate the distance of stimuli based on binocular depth cues.

Everyday Connections

Depth Perception, 3-D Movies, and Optical Illusions
The visual field is projected onto the retinal surface, where photoreceptors transduce light energy into neural signals for the brain to interpret. The retina is a two-dimensional surface, so it does not encode three-dimensional information. However, we can perceive depth. How is that accomplished?

Two ways in which we can extract depth information from the two-dimensional retinal signal are based on monocular cues and binocular cues, respectively. Monocular depth cues are those that are the result of information within the two-dimensional visual field. One object that overlaps another object has to be in front. Relative size differences are also a cue. For example, if a basketball appears larger than the basket, then the basket must be further away. On the basis of experience, we can estimate how far away the basket is. Binocular depth cues compare information represented in the two retinae because they do not see the visual field exactly the same.

The centers of the two eyes are separated by a small distance, which is approximately 6 to 6.5 cm in most people. Because of this offset, visual stimuli do not fall on exactly the same spot on both retinae unless we are fixated directly on them and they fall on the fovea of each retina. All other objects in the visual field, either closer or farther away than the fixated object, will fall on different spots on the retina. When vision is fixed on an object in space, closer objects will fall on the lateral retina of each eye, and more distant objects will fall on the medial retina of either eye (image). This is easily observed by holding a finger up in front of your face as you look at a more distant object. You will see two images of your finger that represent the two disparate images that are falling on either retina.

These depth cues, both monocular and binocular, can be exploited to make the brain think there are three dimensions in two-dimensional information. This is the basis of 3-D movies. The projected image on the screen is two dimensional, but it has disparate information embedded in it. The 3-D glasses that are available at the theater filter the information so that only one eye sees one version of what is on the screen, and the other eye sees the other version. If you take the glasses off, the image on the screen will have varying amounts of blur because both eyes are seeing both layers of information, and the third dimension will not be evident. Some optical illusions can take advantage of depth cues as well, though those are more often using monocular cues to fool the brain into seeing different parts of the scene as being at different depths.

There are two main regions that surround the primary cortex that are usually referred to as areas V2 and V3 (the primary visual cortex is area V1). These surrounding areas are the visual association cortex. The visual association regions develop more complex visual perceptions by adding color and motion information. The information processed in these areas is then sent to regions of the temporal and parietal lobes. Visual processing has two separate streams of processing: one into the temporal lobe and one into the parietal lobe. These are the ventral and dorsal streams, respectively (image). The ventral stream identifies visual stimuli and their significance. Because the ventral stream uses temporal lobe structures, it begins to interact with the non-visual cortex and may be important in visual stimuli becoming part of memories. The dorsal stream locates objects in space and helps in guiding movements of the body in response to visual inputs. The dorsal stream enters the parietal lobe, where it interacts with somatosensory cortical areas that are important for our perception of the body and its movements. The dorsal stream can then influence frontal lobe activity where motor functions originate.

Disorders of the…

Brain: Prosopagnosia
The failures of sensory perception can be unusual and debilitating. A particular sensory deficit that inhibits an important social function of humans is prosopagnosia, or face blindness. The word comes from the Greek words prosopa, that means “faces,” and agnosia, that means “not knowing.” Some people may feel that they cannot recognize people easily by their faces. However, a person with prosopagnosia cannot recognize the most recognizable people in their respective cultures. They would not recognize the face of a celebrity, an important historical figure, or even a family member like their mother. They may not even recognize their own face.

Prosopagnosia can be caused by trauma to the brain, or it can be present from birth. The exact cause of proposagnosia and the reason that it happens to some people is unclear. A study of the brains of people born with the deficit found that a specific region of the brain, the anterior fusiform gyrus of the temporal lobe, is often underdeveloped. This region of the brain is concerned with the recognition of visual stimuli and its possible association with memories. Though the evidence is not yet definitive, this region is likely to be where facial recognition occurs.

Though this can be a devastating condition, people who suffer from it can get by—often by using other cues to recognize the people they see. Often, the sound of a person’s voice, or the presence of unique cues such as distinct facial features (a mole, for example) or hair color can help the sufferer recognize a familiar person. In the video on prosopagnosia provided in this section, a woman is shown having trouble recognizing celebrities, family members, and herself. In some situations, she can use other cues to help her recognize faces.

Definition/Introduction

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.

Issues of Concern

There are varying degrees of impairment in prosopagnosia, including:

• The inability to recognize

• Discriminate

• Identify different or own faces

• Discern differences between faces and surrounding objects.

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.

Clinical Significance

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).

Localization/Pathophysiology

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.

Imaging

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.

Nursing, Allied Health, and Interprofessional Team Interventions

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.