Prosopamnesia is a rare neuropsychological deficit defined by an inability to remember faces. It can be subdivided into two different types, including a 'congenital' and 'acquired' version.

Congenital (developmental) prosopamnesia involves an inborn difficulty in remembering faces, but having intact facial recognition and perception abilities. These abilities can be tested using the Cambridge Face Perception and Cambridge Facial Memory Test, available online. A case report of congenital prosopamnesia demonstrated a subject's inability to neurologically "adapt" to images of faces using functional Magnetic Resonance Imaging (fMRI). The authors relate this deficiency to the brain's inability to maintain a stable perception of the face long enough to encode it into long-term memory.

There is a case report of acquired prosopamnesia in which a subject experienced both retrograde and anterograde facial memory loss after a motorcycle-related head injury.

Prosopamnesia should not be confused with the similar condition prosopagnosia

Prosopagnosia

Prosopagnosia is a disorder of face perception where the ability to recognize faces is impaired, while the ability to recognize other objects may be relatively intact...

, which is characterized by a difficulty perceiving faces. An inability to "see" faces in such a manner will naturally be associated with prosopamnesia, as a facial memory trace cannot be formed without an ability to initially see the face.