Prosopagnosia: meaning, symptoms and causes
Prosopagnosia is the inability to recognise faces. In medicine, agnosia is a generic term for a disorder of sensory discrimination, whether visual, tactile, olfactory or acoustic
The sufferer may be unable to recognise and identify a given object, scent, shape, person or any entity.
Severe cases of prosopagnosia affect 2.5% of the population, at least 7 million people in the United States alone.
To these must be added a 10% of the population that is significantly below average in its ability to recognise people’s faces.
What is Prosopagnosia
The term prosopagnosia is derived from the combination of 2 Greek words: prosopon (face) and agnosia (non-knowledge).
Therefore, the literal meaning of prosopagnosia is ‘non-knowledge of the face’, where ‘non-knowledge’ means ‘failure to recognise’.
Those who suffer from prosopagnosia, for example, are unable to appreciate films, television programmes and plays, as they are unable to recognise the faces of actors or TV characters, even the most famous ones.
At what age does one begin to recognise faces
The ability to recognise people by their faces manifests itself, in humans, in the first months of life.
Infants are also able to recognise animals of other species, such as the face of primates, but this ability quickly disappears and around 3 months they specialise in recognising faces that they are exposed to on a daily basis.
This is why, for example, a Chinese sees all Westerners as similar to each other, whereas to us Westerners they all appear similar and difficult to recognise from each other.
According to researchers, the ability to recognise faces is an innate, hereditary quality that specialises in the first two years of life.
The cells responsible for this task in our brain need good training to develop fully.
These cells are thought to be adjacent to those for recognising other things around us: tests have shown that the same areas of the brain for recognising faces are activated when, for example, a car expert has to distinguish different car models.
The forms of prosopagnosia: symptoms and causes
To date, 2 forms of prosopagnosia are recognised:
- developmental prosopagnosia, congenital-connatal;
- acquired prosopagnosia, occurring in adults.
Let us look at them in detail.
Developmental Prosopagnosia
Developmental prosopagnosia, a very rare, congenital-connatal form, was described in 1995 by a British neurologist, Helen McConachie.
This is attributed to a developmental defect in the facial recognition process, without underlying lesions.
Some authors evoke the possible intervention of a genetic factor.
More precisely, these individuals are unable to associate a face with a person.
Even in early childhood, they do not recognise their loved ones, as they do not associate a face with a distinctive, peculiar and unique sign of a person.
Adult Prosopagnosia
The second, more common form, this time of adult or acquired prosopagnosia, is characterised by the loss of the ability to recognise faces and is a consequence of a brain lesion.
The first cause of occurrence of these lesions, which account for 40% of cases, is a stroke in the cerebral territory tributary to the posterior cerebral artery.
Another common cause of injury is head trauma.
Other causes are less frequent: cerebral haematomas, haemorrhagic stroke, infectious causes such as viral encephalitis, dementia and brain tumours.
In recent years, researchers have focused their efforts on the evolution of diagnostic systems: CT scans and later Nuclear Magnetic Resonance Imaging have made it possible to identify the basis of the problem with sufficient precision.
Prosopagnosia is generally caused by damage to the ‘fusiform gyrus’, a portion of the cerebral cortex at the junction of the occipital and temporal lobes.
How prosopagnosia is treated
Although it has been studied for years, the condition is little known, is not always diagnosed and many struggle to understand how difficult it can be for sufferers to manage.
No treatment exists to date.
Those who suffer from prosopagnosia try to compensate for this lack with some small strategies, usually related to remembering certain details.
A voice, a particularly large nose, a full beard, a certain way of dressing or the presence of glasses are details that can help.
Others recognise people by their posture and gait or by the context in which they find themselves.
This process of recognition by alternative routes is often completely unconscious, so that people with mild forms of prosopagnosia may spend their entire lives unaware that they have a cognitive deficit.
Online, there are support groups and forums for those suffering from prosopagnosia: Ken Nakayama, psychologist and founder of the Vision Sciences Laboratory at Harvard, for example, offers advice and support through his website www.faceblind.org and invites everyone to lend a hand: ‘When we meet somewhere, tell me your name. “Simple,” concludes the expert.
A bit of history: the first reports and Oliver Sacks’ contribution
The first reports of the existence of this disorder date back to the mid-1800s by Jean Martin Charcot and John Hughlings Jackson, but it was not until 1947 when a German neurologist, Joachim Bodamer, first used this name in the description of some clinical cases.
In those pages, in fact, he describes the case of 2 soldiers who were no longer able to recognise familiar faces after brain damage due to a gunshot wound.
One of them, a 24-year-old young man who had received a bullet in the back of the skull, had lost the ability to recognise the faces of his family and friends and even his own in the mirror.
He was, however, able to recognise them through other perceptions such as his voice, his walk, the shape of his glasses and other visual elements.
The neurologist and populariser Oliver Sacks, the author of ‘Awakenings’, became famous for his recounting of his clinical experiences with patients suffering from various brain injuries, which caused bizarre and sometimes mysterious behaviour.
In 1985, he published the essay ‘The Man Who mistook His Wife for a Hat’ in the New Yorker where he told of a man who had a severe form of visual agnosia.
He was unable to recognise faces or their expressions. Furthermore, he could not identify or even categorise objects.
After this story was published, he began receiving letters from people who wanted to compare their difficulties in recognising faces and places with his.
Sacks discovered that the problem of prosopagnosia was more common than he had imagined, all over the world.
He decided to further his own studies to understand what compensation techniques individuals with the condition put in place.
Recognising people by their faces is fundamental to humans and most individuals can distinguish and identify thousands of different faces, which they then associate with a name, identity and other information they have gathered over time.
Face recognition is an essentially innate ability, it is universal and also affects other animal species such as primates.
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