Living/non-living dissociation in a case of semantic dementia: a SPECT activation study

A category-specific dissociation with massive deficits in semantic knowledge of animals and preservation of knowledge of objects was observed in a demented patient with a left inferior temporal cortical atrophy responsible for a deficit of visual semantic processing. When the patient successfully processed the semantic feature of aurally presented object names, a SPECT study showed an activation of the left posterior and middle temporal cortex (Wernicke's area). This haemodynamic pattern was not observed during an unsuccessful processing of animal names that was associated with an activation of the left and right inferior frontal regions. Activation in Wernicke's area probably reflects an adequate matching between auditory lexical input and semantic knowledge for entities with multimodal representations, such as man-made objects. Activation in Broca's area and its right homologous region may correspond to an unsuccessful phonological strategy to evoke semantic features of animals, a category that is mainly visually represented.