The neural representation of nouns and verbs: PET studies

Neuropsychological studies of patients with selective deficits for nouns or verbs have been taken as evidence for the neural specialization of differe nt word classes. Noun deficits are associated with lesions in anterior temp oral regions while verb deficits arise from left inferior frontal lesions. However, neuroimaging studies do not unequivocally support this account, wi th only some studies supporting claims for regional specialization. We carr ied out two PET studies to determine whether there is any regional speciali zation for the processing of nouns and verbs. One study used the lexical de cision task and the other used a more semantically demanding task, i.e. sem antic categorization. We found robust activation of a semantic network exte nding from left inferior frontal cortex into the inferior temporal lobe, bu t no differences as a function of word class. We interpret these data withi n the framework of cognitive accounts in which conceptual knowledge is repr esented within a non-differentiated distributed system.