Morphological complexity reveals verb-specific prefrontal engagement

Abstract

Neuropsychological evidence and recent rTMS studies strongly suggest that damage or inhibition of left prefrontal areas may result in specific impairment of verb morphosyntactic processing. However, functional imaging studies have so far failed to identify an area specifically related to grammatical aspects of verb knowledge. To date very few functional studies have been conducted in languages other than English, a language with limited inflectional morphology. In the present study, we make the hypothesis that neuronal responses for verb grammatical processing may be more or less evident depending on the morphological complexity of verbs in a given language. Exploiting the morphologically rich verbal paradigm typical of the Italian language we implemented an event-related functional MRI design to identify cortical regions that were active when subjects produced nouns or verbs in the context of short phrases. Results showed an area of verb-specific activation for real verbs in a small left frontal region corresponding to the intersection of BA10, BA46 and BA 47. We interpret the results as revealing that language-specific morphological properties may modulate the pattern of grammatical specific activations. Specifically, higher degrees of morphophonological complexity may engage a greater variety of morphophonological operations, thus enhancing the possibility of activations specific for a given grammatical class.