The neural substrates of inferential and referential semantic processing.

INTRODUCTION A distinction has been proposed, on theoretical grounds, between referential and inferential semantic abilities. The former account for the relationship of words to the world, the latter for the relationship of words among themselves. The hypothesis of, at least partially, different neurological underpinnings for this distinction has been supported by the presence of double dissociations in neurological patients between tasks that can be considered to tap the cognitive processes involving these two different classes of semantic knowledge, such as, for example, picture naming (referential) and naming to a verbal definition (inferential). METHODS We report here the results of a functional magnetic resonance experiment, contrasting the pattern of brain activity associated with, respectively, "referential" (picture naming, word-to-picture matching) and "inferential" (naming to definition, word-to-word matching) tasks. RESULTS All tasks activate an extensive set of brain areas involving both hemispheres, corresponding to the "common semantic network". In addition, left hemispheric temporal areas are selectively engaged by the inferential tasks. Conversely, a specific activation of the right fusiform gyrus is associated with the referential tasks. CONCLUSIONS These findings suggest that while inferential tasks, as compared with referential tasks, engage additional processing resources subserved by left hemispheric language areas involved in lexical retrieval, referential tasks (as compared with inferential tasks) recruit right hemispheric areas generally associated with nonverbal conceptual and structural object processing. These findings are compatible with the double dissociations reported in neurological patients.