By Jeslyn Kho
Recognising faces is an integral part of everyday social interactions in society and fundamental in building human connection. It is involved in almost all aspects of our lives- from recognising colleagues and clients in the workplace, teachers and schoolmates; more intimately, our family and loved ones. It is also an evolutionary trait.
Studies have shown that neurons tuned to faces have been found in the superior temporal sulcus (STS) of monkeys. (Perrett, Rolls, & Caan, 1982) Another study has also identified a face-sensitive area in the macaque monkey brain that is topographically homologous to the face-sensitive region on the fusiform gyrus in humans (Tsao et al., 2006).Prosopagnosia deriving from the Greek words prósōpon meaning face and agnōsía, meaning “non-knowledge” is more commonly known as face blindness. It is a neurocognitive disorder whereby the ability to recognise the faces of close friends, family and even one’s own face is impaired while all other neurocognitive functions including visual processing of objects remain operational. The term was first coined by a German neurologist (Joachim Bodamer) in the early 19th century and popularised by Oliver Sacks in his book, “The Man Who Mistook His Wife for a Hat”. So how does this elusive disorder arise in individuals and how exactly does it affect the brain?
Prosopagnosia can be found in two forms: developmental or congenital and acquired. The first case is where an individual has the disorder without having brain damage and the latter due to brain damage (often following a stroke or head injury). It was originally thought that prosopagnosia only arose as a result of acute brain damage, however, research has found that more people may have developmental prosopagnosia than originally thought.
In acquired prosopagnosia, individual range of impairments depends on the extent and the location of the damage therefore causing a unique pattern of symptoms in each patient. The widely different patterns of impairment makes it challenging to pinpoint the face-processing brain regions exactly. However, it is believed that the fusiform gyrus is the region of the brain associated with facial recognition (Kanwisher, McDermott & Chun, 1997). Lesions in parts of the inferior occipital areas and anterior temporal cortex have also been shown to be able to cause prosopagnosia (Gainotti G, Marra C, 2011).
In the case of congenital prosopagnosia, it is not uncommon for it to manifest in early childhood and while development begins early in life, many do not realise they have the impairment until later. A hereditary sub-type of developmental prosopagnosia was also found with a prevalence rate of 2.5%. During this study, 689 randomly selected students participated in a survey in which seventeen developmental prosopagnosics were identified. Family members of the fourteen individuals were surveyed and at least one other affected individual family member was found. (Grüter, T., Grüter, M. & Carbon, 2008). Another study carried out supported this and provided epidemiological evidence. Pedigree trees were also analysed and found that the segregation pattern of hereditary prosopagnosia is fully compatible with autosomal dominant inheritance, explaining why it was so commonly found amongst certain families (Kennerknecht et al. 2006).
Diagnosis has proven to be extremely challenging as there is no definitive test which can establish the diagnosis of a face recognition dysfunction. There are only a few neuropsychological tests that can definitively diagnose prosopagnosia. Common tests include the Benton Facial Recognition Test (BFRT), whereby individuals are asked to identify a face out of the six test faces which best suit a target face. Images do not include hair, clothes or any possible cues which may aid in identification outside of facial recognition. However, the reliability of this test has also been criticised as eleven self-reported prosopagnosics were within the normal range (Duchaine B, Nakayama K,2006). Another common test requires individuals to identify famous faces, however, this test is extremely tough to standardise as upbringing and pop-culture exposure varies greatly with culture and socioeconomic class of individuals.
Prosopagnosia is not always obvious and many individuals are not aware of their impairment until later in life (for congenital prosopagnosics) and in Bodamer’s case: the two soldiers never complained of such a condition. It was his observations, prompts and tests which later revealed their condition (Bodamer, 1947). Even Oliver Sacks himself did not realise he had prosopagnosia until he was middle-aged. Though exposure to the condition has become much more widespread, individuals will never be able to definitively determine if they have the impairment without a proper, standardised, reliable test.
We currently do not have a proper diagnostic test established nor do we have any available form of treatment. While there have been miracle cases where prosopagnosics gain their cognitive abilities to recognise faces, we cannot rely on such events alone. As a result, prosopagnosics have been forced to adapt by using secondary clues like clothing styles, hair colour, skin tone, gait, stature and voice to recognise individuals. However, this proves extremely strenuous on their memory.
Unseen debilitating disorders such as prosopagnosia deserve to be recognised and researched as uncovering the links in facial recognition could lead to a greater understanding of other neural networks and a better quality of life for affected individuals. Further exploration and research are needed to further understand this disorder and uncover possible standardised, reliable diagnostic measures as well as forms of therapy or treatment.
References:
Bodamer, J., Die Prosop‐Agnosie, (1947) Archiv für Psychiatrie und Nervenkrankheiten, 179 6 53.
Duchaine B, Nakayama K (2006). “The Cambridge Face Memory Test: results for neurologically intact individuals and an investigation of its validity using inverted face stimuli and prosopagnosic participants”. Neuropsychologia. 44 (4): 576–85. doi:10.1016/j.neuropsychologia.2005.07.001
Gainotti G, Marra C (2011). “Differential contribution of right and left temporo-occipital and anterior temporal lesions to face recognition disorders”. Front Hum Neurosci. 5: 55. doi:10.3389/fnhum.2011.00055.
Grüter, T., Grüter, M. and Carbon, C.‐C. (2008), Neural and genetic foundations of face recognition and prosopagnosia. Journal of Neuropsychology, 2: 79-97. doi:10.1348/174866407X231001
Kanwisher N, McDermott J, Chun MM (1 June 1997). “The fusiform face area: a module in human extrastriate cortex specialized for face perception”. J. Neurosci. 17 (11): 4302–11. doi:10.1523/JNEUROSCI.17-11-04302.1997.
Kennerknecht, I.; Grueter, T.; Welling, B.; Wentzek, S.; Horst, J. R.; Edwards, S.; Grueter, M. (August 2006). “First report of prevalence of non-syndromic hereditary prosopagnosia (HPA)” (PDF). American Journal of Medical Genetics. 140A (15): 1617–1622. doi:10.1002/ajmg.a.31343
Perrett, D. I., Rolls, E. T., Caan, W., (1982). Visual neurons responsive to faces in the monkey temporal cortex, Experimental Brain Research, 47 329 342, 1982.
Tsao, D. Y., Freiwald, W. A., Tootell, R. B. H., Livingstone, M. S., (2006). A cortical region consisting entirely of face‐selective cells, Science, 311, 5761 670 674, 2006.
Imperial Bioscience Review 