Neural Correlates of Face Processing in Hereditary Prosopagnosia: A Functional MRI Study

For a long time, congenital prosopagnosia has been described as a low incidence anecdotic entity. Only very recently epidemiologic and genetic studies have indicated that its prevalence may in fact amount to 2% of the population, and an autosomal-dominant inheritance pattern was proposed. In neuropsychological terms, hereditary prosopagnosia is not part of a general visual agnosia but may extend to certain deficits in recognition of other, similarly complex visual stimuli. Here we performed a functional MRI study on a group of 18 hereditary prosopagnosics as compared to 18 matched controls. Neutral and emotional faces as well as houses and visual control stimuli were presented in a blocked design. Our behavioral data show that recognition memory for both faces and houses was significantly reduced in prosopagnosics as compared to controls. This effect was most pronounced for faces with neutral expressions. However, the prosopagnosics showed no memory deficits for faces displaying negative emotions such as anger and fear. In terms of functional imaging, both groups displayed a similar, robust pattern of activation when presented with faces. This comprised the right inferior frontal gyrus, right amygdala, and large inferior temporal regions including the fusiform face area. Preliminary comparative analysis showed increased hemodynamics for controls as compared to prosopagnosics in bilateral inferior temporo-occipital areas. Prosopagnosics, on the other hand, displayed enhanced activation in the left inferior frontal sulcus, left amygdala and bilateral anterior insula, thus indicating language and emotion related compensation for face processing deficits.