No abstract

Categories like ''noun'' and ''verb'' represent the basic units of grammar in all human languages, and the retrieval of categorical information associated with words is an essential step in the production of grammatical speech. Studies of brain-damaged patients suggest that knowledge of nouns and verbs can be spared or impaired selectively; however, the neuroanatomical correlates of this dissociation are not well understood. We used event-related functional MRI to identify cortical regions that were active when English-speaking subjects produced nouns or verbs in the context of short phrases. Two regions, in the left prefrontal cortex and left superior parietal lobule, were selectively activated for verb trials compared with noun trials; one region in the left inferior temporal lobe was more active during noun production than verb production. We propose that these regions are involved in representing core conceptual properties of nouns and verbs.actions ͉ cortex ͉ language ͉ objects L inguists since antiquity have classified words into two basic parts of speech, noun and verb (or equivalents thereof) (1, 2). These categories are universal across languages (3) and represent elemental building blocks for grammatical rules that combine single words into phrases and sentences, allowing us to distinguish, for example, well formed sentences (the birds are singing) from ungrammatical sentences (*the sings are birding). Prototypically the class of nouns includes words that denote concrete objects, whereas verbs refer to imageable actions, but this semantic association is hardly restrictive: abstract concepts (the idea) and action words (the kick) can also be named by nouns, and not all verbs name actions (to enjoy) (4). Indeed, beginning at age 4 or 5 normal speakers can even assign grammatical categories to meaningless pseudowords, like the wugs and he zibs (5).What cognitive and neural mechanisms underlie this extraordinary productivity? Some clues have come from the study of brain-damaged patients who appear to have selective difficulties in producing either nouns or verbs (6, 7). Patients with lesions in the left temporal cortex often present with deficits in noun production; left frontal lesions, on the other hand, are associated with impairments in producing verbs (8-11). However, the demonstration of such lesion-deficit patterns has relied, in most cases, on patients' abilities to name pictureable items of different types (objects and actions). This limitation has made it hard to ascertain whether such impairments are truly grammatical in nature, or more reflective of problems in accessing particular aspects of word meaning, like perceptual properties of objects or sensorimotor contingencies associated with actions.Prior functional imaging studies of noun and verb processing (12-16) have been bedeviled by similar confounds. Although some of these experiments have used abstract as well as concrete word stimuli, thereby avoiding the simple conflation of semantic and grammatical categories, they have all nevertheles...

IENF loss at the distal leg is associated with increased neuropathic pain, lower CD4 counts, and higher plasma viral load in HIV-SN. The robustness of the longitudinal measurement of IENF density supports its use in future longitudinal studies and clinical trials.