Prosopagnosia, the inability to recognize human faces

It is very easy to believe that our visual system works by giving us reliable information about the external environment and that the brain it is simply a receptacle for these images that tell us about what is happening in the world. However, the truth is that our nervous system has a very active role in processing this information so that it is coherent and makes sense.

The prosopagnosia it is a phenomenon that serves to remind us of this fact.

What is prosopagnosia?

It is, in short, a failure of our nervous system whose consequence is that, who experiences it, is not able to recognize human faces. That means that despite having perfect eyes and being able to collect all the information visual relative to a person's face, it is not able to detect the patterns that turn that face into something unique. Definitely: we see the face but we do not recognize it.

Prosopagnosia is a type of visual agnosia, since there are several classes of neurological disorders in which what is seen is not recognized in a normal way by the brain. It is also one of the best known types of agnosia thanks to, among other people,

neurologist Oliver Sacks, recently deceased, as he spoke about his experience with visual agnosia patients in one of his most famous books: The man who mistook his wife for a hat.

How do people with prosopagnosia perceive faces?

People with prosopagnosia perceive faces as a blurry image, and are able to notice the existence of the typical organs of a face (eyes, nose, etc.) but not their exact location within the set. However, there are cases in which they can recognize some characteristics of the face of a few people, or the time to roughly perceive the faces of certain groups (people of a certain sex, or with Asian features, etc.).

Prosopagnosia does not make it impossible to recognize someone, since people with this neurological disorder can identify the rest by their way of walking, their clothes, their hair ...

What are the causes of prosopagnosia?

Prosopagnosia can be due to lesions in specific areas of the brain, but it can also be a condition that you are born with. The part of the brain that functions abnormally in people with this disorder is thought to be the fusiform gyrus, an area of ​​the cerebral cortex located in the temporal lobe, near the temples. Thanks to the fusiform turn we are extremely sensitive to all the subtleties that a human face can contain, and also thanks to him we have an unprecedented propensity to see faces in all kinds of things, including inanimate objects (these "illusions" are called pareidolias).

When the fusiform gyrus or the neural networks that connect this area to other parts of the brain function abnormally, this can translate into inability to detect the visual patterns necessary to "see" a face as a whole.

The brain has mechanisms to overcome this condition

However, in a sense, the brain does get visual information about faces, so other areas of the nervous system can process this information subconsciously. This explains why people with prosopagnosia show emotional activation when seeing the faces of close people (their mother, her friends, etc.), even though they do not consciously recognize them. This occurs because, despite the fact that the fusiform gyrus does not work well, part of the visual information is processed in parallel by the limbic system, in charge of causing them to be born. emotional responses.