The repetition paradigm: enhancement of novel metaphors and suppression of conventional metaphors in the left inferior parietal lobe.

The neural mechanisms underlying the process of understanding novel and conventional metaphoric expressions remain unclear largely because the specific brain regions that support the formation of novel semantic relations are still unknown. A well established way to study distinct cognitive processes specifically associated with an event of interest is to repeatedly present the same stimulus. The aim of the current study is to examine the neural signatures associated with forming new metaphoric concepts by repeatedly presenting novel as well as conventional metaphors. In an fMRI study, 11 subjects read novel and conventional two-word metaphoric expressions and decided whether the expressions were meaningful. Prior to the study, participants were presented with half of the conventional metaphors and half of the novel metaphoric expressions. The present results revealed that whereas repeated exposure to conventional metaphors elicited repetition suppression within the left supramarginal gyrus, no brain areas showed repetition suppression effects during the repeated exposure of novel metaphors. However, repetition enhancement effects for novel metaphors were found in several brain areas including the bilateral inferior parietal gyri. These findings suggest that the left and right supramarginal gyri are both involved in the conceptualization and the storage of novel semantic relations. This study is important to develop theoretical accounts of the formation of conceptual knowledge for both familiar and novel information.