Cortical signatures of noun and verb production

doi:10.1073/pnas.0504142103

Cortical signatures of noun and verb production

^†Department of Psychology, Harvard University, 33 Kirkand Street, Cambridge, MA 02138; and ^‡Department of Neurology, Massachusetts General Hospital, 55 Fruit Street, Boston, MA 02114

Edited by Edward E. Smith, Columbia University, New York, NY, and approved December 5, 2005 (received for review May 18, 2005)

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.

Footnotes

↵ § To whom correspondence should be addressed. E-mail: caram{at}wjh.harvard.edu.
Author contributions: K.A.S., L.R.M., and A.C. designed research; K.A.S. and L.R.M. performed research; K.A.S., L.R.M., and A.C. analyzed data; and K.A.S., L.R.M., and A.C. wrote the paper.
Conflict of interest statement: No conflicts declared.
This paper was submitted directly (Track II) to the PNAS office.
Abbreviation: fMRI, functional MRI.
Data deposition: The neuroimaging data have been deposited with the fMRI Data Center, www.fmridc.org (accession no. 2-2006-120NY).
↵ ¶ Noun production was also correlated with decreases in activation of the left superior frontal gyrus and right parahippocampal gyrus. These decreases could reflect task-related inhibition for noun trials, a return to baseline of areas of unsuspected activation in other phases of the experiment (e.g., verb trials, stimulus phrase processing), or some other poorly understood modulation of cortical activity. In any case, we have no pretheoretical notions about the role of these two areas in lexical production. There is some evidence that the right parahippocampal gyrus specifically is involved in processing the spatial location or background context of perceived objects (21), and that damage to this area impairs visual-spatial memory without affecting object recognition (22). If this is true, perhaps right parahippocampal deactivation in noun production reflects an inhibition of context-specific object processing in favor of more “categorical” processes.
↵ ∥ It could be argued that no change trials can be performed by relying on working memory, rather than by truly engaging operations involved in word production. We believe that this is unlikely in the present task, because the context demands syntactic analysis at the phrase level on every trial. However, we are mindful of this objection, and therefore we report any differences in the behavioral or physiologic response to change and no-change trials.
↵ †† A separate analysis was conducted with only the change trials. In this model, there were 12 event types; all other parameters were the same. Patterns of activation for the contrasts (noun - verb) and (verb - noun) were congruent with those obtained in the larger analysis, allowing for some variability attributable to decreased power (increased random error). Because the results of these two analyses were similar, we report only the more powerful model.