Prosopagnosia, the inability to recognize human faces.

We explain the causes and symptoms of this strange condition.

It is very easy to believe that our visual system works by giving us reliable information from the external environment and that the brain 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 plays a very active role in processing this information so that it is coherent and makes sense.

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

What is prosopagnosia?

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

Prosopagnosia is a type of visual agnosiaprosopagnosia, as there are several kinds 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 others, the recently deceased neurologist Oliver Sacks, who 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 blur-like 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 whole. However, there are cases in which they can recognize some characteristics of the face of a few people, or be better at perceiving in an approximate way the faces of certain groups (people of a certain sex, or with Asian features, etc.).

Prosopagnosia does not make the task of recognizing someone impossible.People with this neurological disorder can identify others by the way they walk, their clothes, their hair...

What are the causes of prosopagnosia?

Prosopagnosia may be due to lesions in specific areas of the brain, but it can also be a condition with which one is born. It is believed that the part of the brain that functions abnormally in people with this disorder is that of the fusiform gyrusThe fusiform gyrus, an area of the cerebral cortex located in the temporal lobe, near the temples. Thanks to the fusiform gyrus we are extremely sensitive to all the subtleties that a human face may contain, and also thanks to it we have an unheard-of 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 with other parts of the brain function abnormally, this can result in an inability to see faces in all kinds of things, including inanimate objects, this can result in an 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 receive 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 they see the faces of people close to them (their mother, their friends, etc.), even though they do not consciously recognize them. This occurs because, although the fusiform gyrus does not function well, part of the visual information is processed in parallel by the limbic system, which is responsible for eliciting emotional responses.