Pure topographical disorientation--the anatomical basis of landmark agnosia.

We used MRI studies of four patients to investigate the lesions responsible for landmark agnosia. A detailed investigation of the relationship between the symptoms and the lesions suggests that the right posterior part of the parahippocampal gyrus is critical for the acquisition of novel information about buildings and landscapes, and that the same region plus the anterior half of the lingual gyrus and the adjacent fusiform gyrus play an important role in the identification of familiar buildings and landscapes. Furthermore, the lesion responsible for prosopagnosia, which frequently occurs with landmark agnosia, seems to involve the posterior half of the lingual and fusiform gyri. This suggests that the lesions responsible for landmark agnosia and prosopagnosia are close to each other, but distinct.