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 cognit ive defects underlying category-specific disorders for living and non-livin g things. One model assumes that the living/non-living distinction is the b y-product of a more basic dichotomy, contingent upon the different weightin g that visuo-perceptual and functional attributes have in the identificatio n 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 existin g between perceptual and functional features in living and non living thing s may be more important than the weighting of these features. Each of these models makes implicit assumptions about the extent and the lo calization of brain lesions provoking category-specific disorders. However, it must also be considered that these disorders are heterogeneous in natur e, 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 nonliving disorders. Our findings showed that there is a correlation between the loc us of lesion and the patterns of categorical impairment: (a) a bilateral in jury to the antero-mesial and inferior parts of the temporal lobes was foun d in patients with a category-specific semantic impairment for living thing s; (b) a lesion of the infero-mesial parts of the temporo-occipital areas o f the left hemisphere was found in a group of patients showing a specific l exical impairment for members of the 'plants' category; (c) an extensive le sion of the areas lying on the dorso-lateral convexity of the left hemisphe re was found in patients with a category-specific semantic impairment for m an-made artefacts. Taken together, these results seem to show that the cate gory-specific disorder is crucially related to the kind of semantic informa tion processed by the damaged areas.