What the locus of brain lesion tells us about the nature of the cognitive defect underlying category-specific disorders: a review.

Different models have been proposed to account for the nature of the cognitive defects underlying category-specific disorders for living and non-living things. One model assumes that the living/non-living distinction is the by-product of a more basic dichotomy, contingent upon the different weighting that visuo-perceptual and functional attributes have in the identification of members of these categories. A second model submits that evolutionary pressure resulted in the elaboration of dedicated neural mechanisms for the domains of living (animals and plants) and non-living (artefacts) things. A third model proposes that the different level of interconnections existing between perceptual and functional features in living and non living things may be more important than the weighting of these features. Each of these models makes implicit assumptions about the extent and the localization of brain lesions provoking category-specific disorders. However, it must also be considered that these disorders are heterogeneous in nature, resulting from defects located at the semantic, lexical or visual level. In the present review of the literature, we kept this distinction in mind in trying to analyze the neuroanatomical correlates of living and non-living disorders. Our findings showed that there is a correlation between the locus of lesion and the patterns of categorical impairment: (a) a bilateral injury to the antero-mesial and inferior parts of the temporal lobes was found in patients with a category-specific semantic impairment for living things; (b) a lesion of the infero-mesial parts of the temporo-occipital areas of the left hemisphere was found in a group of patients showing a specific lexical impairment for members of the 'plants' category; (c) an extensive lesion of the areas lying on the dorso-lateral convexity of the left hemisphere was found in patients with a category-specific semantic impairment for man-made artefacts. Taken together, these results seem to show that the category-specific disorder is crucially related to the kind of semantic information processed by the damaged areas.