ABSTRACT
Category-specific deficits were first reported in individual subjects who had suffered herpes simplex encephalitis (Sartori & Job, 1988; Silveri & Gainotti, 1988; Warrington & Shallice, 1984) and motor vehicle trauma (Riddoch & Humphreys, 1987). Since then similar deficits have been reported in singlecase and group studies of subjects with Alzheimer’s disease (AD). In this chapter, we examine these reports and consider how this phenomenon relates to the disease and what it can tell us about brain organisation of semantic memory. The neuropathology of AD involves the progressive formation of neurofibrillary tangles and neuritic plaques concentrated in the cortical regions involved in the highest order of cognitive function, the associative cortex (lateral temporal, parietal, and frontal lobes), as well as in the limbic system (in particular the hippocampus). Focal brain lesions have the potential of informing us about the functional organisation of cognition by demonstrating that certain brain processes can be dissociated from each other. In contrast, the gradual, progressive, and more diffuse loss seen in AD provides critical clues to the organisation of semantic memory through studies of the dedifferentiation of knowledge systems.
