The role of the two hemispheres in processing metaphoric language is controversial. While some studies have reported a special role of the right hemisphere (RH) in processing metaphors, others indicate no difference in laterality relative to literal language. Some studies have found a role of the RH for novel/unfamiliar metaphors, but not
conventional/familiar metaphors. It is not clear, however, whether the role of the RH
is specific to metaphor novelty, or whether it reflects processing, reinterpretation or
reanalysis of novel/unfamiliar language in general. Here we used functional magnetic
resonance imaging (fMRI) to examine the effects of familiarity in both metaphoric and
non-metaphoric sentences. A left lateralized network containing the middle and inferior
frontal gyri, posterior temporal regions in the left hemisphere (LH), and inferior frontal
regions in the RH, was engaged across both metaphoric and non-metaphoric sentences;
engagement of this network decreased as familiarity decreased. No region was engaged
selectively for greater metaphoric unfamiliarity. An analysis of laterality, however, showed that the contribution of the RH relative to that of LH does increase in a metaphorspecific manner as familiarity decreases. These results show that RH regions, taken by themselves, including commonly reported regions such as the right inferior frontal gyrus (IFG), are responsive to increased cognitive demands of processing unfamiliar stimuli, rather than being metaphor-selective. The division of labor between the two hemispheres, however, does shift towards the right for metaphoric processing. The shift results not because the RH contributes more to metaphoric processing. Rather, relative to
its contribution for processing literals, the LH contributes less.