A neural basis for the retrieval of conceptual knowledge.

Both clinical reports and systematic neuropsychological studies have shown that patients with damage to selected brain sites develop defects in the retrieval of conceptual knowledge for various concrete entities, leading to the hypothesis that the retrieval of knowledge for entities from different conceptual categories depends on partially segregated large-scale neural systems. To test this hypothesis, 116 subjects with focal, unilateral lesions to various sectors of the telencephalon, and 55 matched controls, were studied with a procedure which required the visual recognition of entities from three categories--unique persons, non-unique animals and non-unique tools. Defective recognition of persons was associated with maximal lesion overlap in right temporal polar region; defective recognition of animals was associated with maximal lesion overlap in right mesial occipital/ventral temporal region and also in left mesial occipital region; and defective recognition of tools was associated with maximal lesion overlap in the occipital-temporal-parietal junction of the left hemisphere. The findings support the hypothesis that the normal retrieval of knowledge for concrete entities from different conceptual domains depends on partially segregated neural systems. These sites may operate as catalysts for the retrieval of the multidimensional aspects of knowledge which are necessary and sufficient for the mental representation of a concept of a given entity.