Just ran across this poster presented at the Organizing for Brain Mapping's Annual Meeting in 2004. Sahin, Halgren, Ubert, Dale, Schomer, Wu and Pinker looked at the fMRI and EEG changes associated with a number of language tasks, and one of the questions they asked was whether activation characteristics were different for nouns and verbs. This study did not find that they were.
In my sketch of a neurolinguistic theory, verbs are first order modifiers and are distinct from adjectives in that they mediate properties and relationships between nouns. (In this sense, intransitive verbs are more similar to adjectives than to transitive verbs.) I also postulate that nouns and first order modifiers should have identifiably different neural correlates. I have not yet completed a literature search (obviously, if I'm citing posters from 2004.) However, even if such different neural correlates obtain, then I think it the task design here was not necessarily adequate to capture such differences, because the participants were asked to morphologically modify the nouns and verbs in isolation, rather than in situ, in grammatical relation to each other.
Another interesting experiment would be to give the participants nonsense words and new affixing rules (i.e. not revealing the part of speech of the nonsense word, i.e. ("if the word has a t in it, add -pex to the end, otherwise, add -peg"), and look for any difference relative to neural correlates of morphological tasks done in real words.
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