Prosopamnesia (Greek: προσωπον = "face", αμνησια = forgetfulness) is a selective neurological impairment in the ability to learn new faces. There is a special neural circuit for the processing of faces as opposed to other non-face objects. Prosopamnesia is a deficit in the part of this circuit responsible for encoding perceptions as memories.
Overview
Prosopamnesia presents itself in patients as an inability to recognize people they have previously encountered based on their faces. In this way, it is very easily mistaken as prosopagnosia, which is an inability to perceive or recognize faces. Prosopagnosia is a deficit that occurs earlier in the neural circuit while the facial stimuli is being processed, whereas prosopamnesia takes effect when the brain attempts to encode the processed facial stimuli into memory. Because the distinction between prosopamnesia and prosopagnosia is so close in the neurological circuit, the only phenotypic difference between the two is in the breadth of faces to which a patient's symptoms apply. Prosopagnosics cannot recognize faces, even of people within their own families over the span of a lifetime. Prosopamnesiacs show a memory for facial stimuli that they learned prior to the onset of their condition (in the case of acquired prosopamnesia) or for facial stimuli that they have encountered repeatedly for long periods of time (in the case of congenital prosopamnesia).
There are currently only two diagnosed cases of prosopamnesia. This is likely due to the fact that it can easily be misdiagnosed as prosopagnosia based on symptoms. Some doctors have even recognized distinctions in deficits of facial perception and facial memory encoding and classified them as subfamilies of prosopagnosia. This lack of consistency within the scientific community for classifying patients with facial memory encoding deficits is one reason that prosopamnesia has such rare diagnosis. Most of the current knowledge about how prosopamnesia works within the brain is hypothesized, but not proven, due to lack of case studies. As doctors become aware of the distinction between prosopagnosia and prosopamnesia, proper and more frequent diagnosis of prosopamnesia may occur.
Symptoms
Symptoms of prosopamnesia may include: Difficulty recognizing people, especially when encountered outside any previous or familiar context Use of non-facial cues such as hair, gait or glasses to identify people Need to meet people many times before being able to remember their names Trouble keeping track of characters in movies or TV shows Social anxiety Having a memory for the faces of people encountered before the brain damage occurred (acquired case only)
Cause
Prosopamnesia can be either genetically inherited (developmental) or acquired as a result of incidental brain damage. The exact cause of prosopamnesia is unverified, because there are only two known cases. Each group of doctors that studied the currently diagnosed prosopamnesiacs proposed slightly different explanations for the cause. Dr. Tippett's group described its cause as a "disconnection between learning mechanisms and domain-specific representations". In other words, a general dysfunction in the brain's ability to encode a representation of facial stimuli into memory. Dr. Williams's group hypothesized that prosopamnesia is caused by an inability of the FFA to maintain a stable representation of new faces long enough for them to be encoded into memory. This conclusion is partially based on the patient's differing responses to familiar and unfamiliar faces within the FFA as seen in blood-oxygen-level dependent (BOLD) responses recorded during functional magnetic resonance imaging (fMRI) tests.