Are semantic systems separately represented in the brain? The case of living category impairment.

Following herpes encephalitis, a patient showed impaired knowledge of animals, fruits and vegetables, flowers and food (so called living things categories), whatever the modality in which stimuli were presented and responses were given. A series of experiments showed that the deficit specifically affected the ability to retrieve the perceptual features of the living stimuli defining their shape, while knowledge of their functional-encyclopedic properties was preserved. The patient had no problems with man-made objects, except when the recall of their colour, or the identification of their sound was requested. It is argued that the retrieval of the perceptual features was potentially disrupted for every type of category, but that the block was compensated for man-made objects, because the close correspondence between shape and function that characterises them provided an alternative route to access their structured form representations. On this account, the selective deficit for living categories seems contingent on the interaction between an overall cognitive impairment--the deficit in retrieving perceptual features--and some intrinsic properties of the stimulus--the factors that have modelled its form--and cannot be taken as evidence that semantic systems are allotted to separate cerebral areas.