Impairments in the Face-Processing Network in Developmental Prosopagnosia and Semantic Dementia

Abstract

Background: Developmental prosopagnosia (DP) and semantic dementia (SD) may be the two most common neurologic disorders of face processing, but their main clinical and pathophysiologic differences have not been established. To identify those features, we compared patients with DP and SD.

Methods: Five patients with DP, five with right temporal-predominant SD, and ten normal controls underwent cognitive, visual perceptual, and face-processing tasks.

Results: Although the patients with SD were more cognitively impaired than those with DP, the two groups did not differ statistically on the visual perceptual tests. On the face-processing tasks, the DP group had difficulty with configural analysis and they reported relying on serial, feature-by-feature analysis or awareness of salient features to recognize faces. By contrast, the SD group had problems with person knowledge and made semantically related errors. The SD group had better face familiarity scores, suggesting a potentially useful clinical test for distinguishing SD from DP.

Conclusions: These two disorders of face processing represent clinically distinguishable disturbances along a right hemisphere face-processing network: DP, characterized by early configural agnosia for faces, and SD, characterized primarily by a multimodal person knowledge disorder. We discuss these preliminary findings in the context of the current literature on the face-processing network; recent studies suggest an additional right anterior temporal, unimodal face familiarity-memory deficit consistent with an "associative prosopagnosia."

FIGURE 1

Representative brain magnetic resonance images (coronal views) from our study participants. Panel 1: This image, from the only member of the developmental prosopagnosia group who had an available scan, shows a normal anterior temporal region. Panels 2–6: One image is shown from each of the patients with semantic dementia. All have atrophy involving the inferior lateral anterior temporal lobes bilaterally, but more pronounced on the right, consistent with semantic dementia.

FIGURE 2

Example of a display for Face Recognition by Name. The examiner asks the participant, “Which one is Adolph Hitler?” The three faces other than Hitler’s (top right) are a semantically related familiar face (Joseph Stalin, top left), a physically similar but generally unfamiliar face (bottom left), and a familiar but semantically unrelated and only partially similar-looking face (Charlie Chaplin, bottom right). We kept the large details of all the faces at least somewhat similar to avoid presenting a salient difference of cue.