Category-specific knowledge deficit for animals in a patient with herpes simplex encephalitis.

A large number of brain-damaged patients with heterogeneous category-specific deficits have been reported in literature. This has given rise to different theories concerning the processing of semantic knowledge. In this paper we report the case of K.C. who, after a bout of herpes simplex encephalitis, displayed a category-specific impairment restricted to the knowledge of animals, irrespective of input modality. K.C.'s magnetic resonance imaging (MRI) showed multiple bilateral antero-mesial and inferior temporal lesions. Although she was impaired for both the perceptual (visual and auditory) and functional/associative attributes of animals, she performed normally in an object-reality decision task involving pictures of animals and nonanimals. The dissociation between K.C.'s intact structural description system and her impaired semantic knowledge is interpreted according to hierarchical interactive theory (HIT), which assumes that conceptual knowledge is hierarchically organized in separate but interactive multiple knowledge substores. K.C.'s results indicate that her access to a presemantic structural description system was intact so that her impairment on animal semantic knowledge arose later at a conceptual stage of the object recognition system. Furthermore, K.C.'s deficits indicate selective disruption of a special class of animate concepts within the broad category of living things, which seems best explained by the "domain-specific knowledge theory" proposed by Caramazza and Shelton.