Word and picture matching: a PET study of semantic category effects

We report two positron emission tomography (PET) studies of cerebral activa tion during picture and word matching tasks, in which we compared directly the processing of stimuli belonging to different semantic categories (anima te and inanimate) in the visual (pictures) and verbal (words) modality. In the first experiment, brain activation was measured in eleven healthy ad ults during a same/different matching task for textures, meaningless shapes and pictures of animals and artefacts (tools). Activations for meaningless shapes when compared to visual texture discrimination were localized in th e left occipital and inferior temporal cortex. Animal picture identificatio n, either in the comparison with meaningless shapes and in the direct compa rison with non-living pictures, involved primarily activation of occipital regions, namely the lingual gyrus bilaterally and the left fusiform gyrus. For artefact picture identification, in the same comparison with meaningles s shape-baseline and in the direct comparison with living pictures, all act ivations were left hemispheric, through the dorsolateral frontal (Ba 44/6 a nd 45) and temporal (Ba 21, 20) cortex. In the second experiment, brain activation was measured in eight healthy ad ults during a same/different matching task for visually presented words ref erring to animals and manipulable objects (tools); the baseline was a pseud oword discrimination task. When compared with the tool condition, the anima l condition activated posterior left hemispheric areas, namely the fusiform (Ba 37) and the inferior occipital gyrus (Ba 18). The right superior parie tal lobule (Ba 7) and the left thalamus were also activated. The reverse co mparison (tools vs animals) showed left hemispheric activations in the midd le temporal gyrus (Ba 21) and precuneus (Ba 7), as well as bilateral activa tion in the occipital regions. These results are compatible with different brain networks subserving the i dentification of living and non-living entities; in particular, they indica te a crucial role of the left fusiform gyrus in the processing of animate e ntities and of the left middle temporal gyrus for tools, both from words an d pictures. The activation of other areas, such as the dorsolateral frontal cortex, appears to be specific for the semantic access of tools only from pictures. (C) 1999 Elsevier Science Ltd. All rights reserved.