Effects of noun-verb homonymy on the neural correlates of naming concrete entities and actions.

The neural correlates of naming concrete entities such as tools (with nouns) and naming actions (with verbs) are partially distinct: the former are linked to the left inferotemporal (IT) region, whereas the latter are linked to the left frontal opercular (FO) and left posterior middle temporal (MT) regions. This raises an intriguing question: How would such neural patterns be influenced by noun-verb homonymy, specifically, naming tasks in which the target words denote objects or actions (e.g., "comb")? To explore this, we conducted a PET study in which 10 normal participants named visually presented tools or actions. The factor of homonymy yielded interesting effects: For tools, non-homonymous nouns (e.g., "camera") activated left IT, whereas homonymous nouns (e.g., "comb") activated both left IT and left FO. For actions, non-homonymous (e.g., "juggle") and homonymous (e.g., "comb") verbs activated left FO, MT, and IT, but there was evidence that the FO and MT activations were less widespread for the homonymous verbs. We also found that retrieval of the same exact words (e.g., "comb" and "comb") produced differential activation in left MT-there was greater MT activation when the words were being used to name actions, than when they were being used to name tools. Our results suggest that noun-verb homonymy has an important influence on the patterns of neural activation associated with words denoting objects and actions, and that even when the phonological forms are identical, the patterns of neural activation are different according to the demands of the task.