Nouns and verbs in the brain: A meta-analysis of 27 fMRI and PET studies

Although the functional independence of noun and verb lexical retrieval has been reliably established, it is not clear whether the processing of these grammatical classes recruits separate neural circuits [1]. Contrasting results might have emerged because different studies used different experimental and baseline tasks. The meta‑analysis described in this study aims at identifying (i) brain regions that are consistently associated with a given grammatical class across different tasks, and (ii) brain areas whose grammatical‑class specificity is modulated by the task used. We considered 620 activation peaks reported in 27 neuroimaging studies on nouns and verbs. A hierarchical cluster algorithm was used in order to automatically segregate groups of coordinates into separate clusters. This procedure produced a set of 52 clusters, which were assessed with a binomial test for specificity for grammatical class and/or task, and with a Fisher test for task‑by‑grammatical class interaction. One cluster was associated with nouns across different tasks in the right superior temporal gyrus; verb‑specific clusters were instead observed in the middle temporal gyrus bilaterally, in the right precuneus and in the left lingual gyrus. Other four clusters – located in the left inferior frontal gyrus, in the left insula, and in the left middle occipital gyrus – showed a task‑by‑grammatical class interaction. The impact of these results on the current neuroanatomical theories of noun and verb processing [2] will be discussed. [1] Berlingeri, M. et al. (2008), Cognitive Neuropsychology, 25, 528‑558. [2] Cappa, S. & Perani, D. (2003), Journal of Neurolinguistics, 16, 183‑189.