We investigated the areas of the brain that are involved in the storage of lexical representations of verbs and nouns by localizing the brain lesions causing disproportionate impairment to the retrieval of these lexical categories in a sample of 20 Italian aphasic patients. In the majority of patients, with disproportionate impairment of nouns, the lesion involved the medial part of the middle and inferior left temporal gyri. In contrast, patients with disproportionate impairment of verbs clustered in two major subsets: either left posterior temporal lobe and inferior parietal lesions, or extensive left fronto-temporal lesions.

In a second analysis, an attempt was made to disentangle the effect of imageability from disproportionate verb impairment: in at least two cases, verb damage was found to persist even after the imageability effect was removed. The relationship between imageability and actionality was also investigated: no interaction was found between these variables. A last analysis focused on the mechanisms underlying temporo-parietal damage in verb-impaired patients. Results indicate a critical role of the temporo-parietal area when retrieving verbs, irrespective of their degree of actionality.