Prosopagnosia after unilateral right cerebral infarction.

Abstract

Sirs: Recently, there have been substantial contributions of functional imaging methods to the delineation of face responsive regions in the human brain, particularly in the fusiform gyrus (FFA, fusiform face area) [1]. There is, however, still no agreement upon the exact pathoanatomical correlates of prosopagnosia, the acquired inability to recognize familiar persons by the mere sight of their faces [2]. A widely accepted view claims that damage to both hemispheres is its necessary precondition [3]. Reports of prosopagnosia following isolated right-hemispheric lesions are still regarded as controversial.We wish to add two new case observations to this discussion.We argue that unilateral, right temporo-occipital infarction is in fact sufficient to cause the syndrome and will propose a unifying hypothesis. The first patient, a 85-year-old right-handed former manager, was admitted with a slight left hemiparesis, left hemisensory loss and a left homonymous hemianopia which were due to an ischemic infarct in the right posterior cerebral artery territory. Neuropsychological examination two weeks later showed left hemineglect on reading, letter cancellation, line bisection, and object drawing from memory. Oculomotor exploration of the left hemispace was reduced, and the patient’s head was continuously, albeit slightly turned to the right. Visual and tactile identification of real objects was within normal limits, but the patient was severely impaired in the recognition of line drawings, particularly if presented in an unconventional view (8 out of 30 correct in the silhouettes subtest of the “Visual Object and Space Perception Battery (VOSP)” [4]; normal range: ≥15). The patient primarily focused on local object features, while he was hardly able to integrate the single details into a whole. Most striking, however, was his impairment in face recognition. An inability to recognize the hospital staff was noticed on the ward. On formal testing with famous faces, he only recognized two out of ten. A portrait of the German head of government was mistaken for an image of the clinical investigator “at a younger age” (the age relation of the two, in fact, being the converse). When confronted with photographs showing his wife amidst other persons, he failed to identify her. Moreover, out of two photographs of himself he took one as showing his wife and only succeeded in correctly interpreting the second picture because of a peculiar detail of clothing. Although able to identify a face as such, he failed to integrate its features into a whole that represented a specific individual. A striking example was his misinterpretation of a laughing face as sad after the photograph had been inverted. He had focused on the corners of the mouth only and whether they were directed upwards or downwards. Magnetic resonance imaging (MRI) revealed a right-sided infarction that included the occipitotemporal region with the FFA and also affected parts of the thalamus and the internal capsule as well as the splenium. The left hemisphere was spared (Fig. 1). The second patient, retired as a railway engineer eight years previously after myocardial infarction, presented to the emergency room at the age of 57 because of sudden dizziness and the inability to recognize his wife’s face. He had homonymous left upper quadrantanopia and left lower quadrant dyschromatopsia in association with hemianopic dyslexia, corresponding to an acute ischemic infarction in the right posterior cerebral artery territory as delineated on neuroimaging. He was seen for formal neuropsychological examination three days later. There was no hemineglect, no memory disorder or other cognitive deficits. However, the severe impairment in face recognition was confirmed. In spite of his ability to differentiate between faces and non-faces, the patient failed to recognize the staff on the ward. Looking at his own face in a mirror he experienced it as surprisingly alien. He had the same impression of absent familiarity if he saw photographs of his wife or of relatives. Out of 27 photographs of famous faces he identified only 8, all of which were characterized by specific features such as the bushy eyebrows of a certain politician or other characteristic paraphernalia that he used for analysis. His tendency towards a piece meal approach was corroborated by the difficulties he displayed in differentiating the gender, age and emotional expression of the faces presented, particularly if they were inverted. In addition, he had the impression that two photographs depicted two different people, if in fact it was the same person, but with a different facial expression. This patient, just as the first, displayed a substantial deficit in identifying line drawings that were presented in a non-canonical view (VOSP-silhouettes: 6/30). Identification of real objects and phoLETTER TO THE EDITORS