Pathways to lexical ambiguity: fMRI evidence for bilateral fronto-parietal involvement in language processing

• Event-related fMRI investigated the contribution of the right hemisphere in linguistic tasks.
• Bilateral involvement of the pars opercularis (Brodmann’s area 44).
• Bilateral involvement of the supramarginal gyrus of the inferior parietal lobule.
• Strong connections between areas 44 and 40 through SLF III.
• Delineate anterior-posterior language processing system bilaterally.
• Increased right hemisphere involvement during metaphorical interpretations.

Numerous functional neuroimaging studies reported increased activity in the pars opercularis and the pars triangularis (Brodmann’s areas 44 and 45) of the left hemisphere during the performance of linguistic tasks. The role of these areas in the right hemisphere in language processing is not understood and, although there is evidence from lesion studies that the right hemisphere is involved in the appreciation of semantic relations, no specific anatomical substrate has yet been identified. This event-related functional magnetic resonance imaging study compared brain activity during the performance of language processing trials in which either dominant or subordinate meaning activation of ambiguous words was required. The results show that the ventral part of the pars opercularis both in the left and the right hemisphere is centrally involved in language processing. In addition, they highlight the bilateral co-activation of this region with the supramarginal gyrus of the inferior parietal lobule during the processing of this type of linguistic material. This study, thus, provides the first evidence of co-activation of Broca’s region and the inferior parietal lobule, succeeding in further specifying the relative contribution of these cortical areas to language processing.