| The double-dissociation in verb and noun deficits observed in a broad range of neurological patients (e.g. aphasics) suggests that distinctive neural mechanisms may exist for these word categories. Among the many differences between nouns and verbs, conceptual differences have not been considered in neuroimaging research. Verbs represent processes or events which dynamically occur among entities, so they hold relational information among entities, so-called thematic information. In contrast, nouns refer to the entities, so they hold perceptual information specific for those references. Thus, I hypothesized that verb concepts rely more heavily on Wernicke's area to integrate thematic information while nouns elicit more activation related to perceptual memory in regions such as the fusiform gyrus. To test these hypotheses, semantic priming effects were investigated for relations within and between these word classes by using functional MRI. Behavioral priming effects, indexed by faster response time, were observed differently across relationships. Brain response to a certain category of nouns, i.e. animal names, was observed in the lateral fusiform gyrus. This response was suppressed when an animal name was preceded by another animal name (e.g., scorpion-spider). Importantly, it was also suppressed when the noun was preceded by an action verb (e.g., crawl-spider); additionally the verb-noun pair increased activation in Wernicke's area, indicating an additional process to integrate argument information. On the contrary, animal primes did not result in the suppression of activation for action verb targets (e.g., hamster-jiggle); instead it elicited greater activation in the left anterior inferior frontal gyrus. For action verb targets, action verb primes (e.g., wobble-jiggle) suppressed activation in the motor cortex as well as Wernicke's area. Based on current results, I suggest two things; (i) perceptual information of an object or an action is embodied in sensory-motor cortices, and (ii) relational information embedded in verb concepts elicits an integral process which seems specialized in Wernicke's area. |
