Mashal, N. 1 & Subramaniam, K. 2
1 School of Education.Bar-Ilan University.Ramat-Gan.Israel
2 Department of Psychiatry. University of California. San Francisco.USA
Previous studies have shown that understanding novel and conventional metaphoric expressions relies on dissociable brain mechanisms. This is not surprising given that the cognitive processes associated with comprehending novel and conventional metaphors are distinct: understanding conventional metaphors requires meaning retrieval whereas understanding novel metaphors require the formation of distant semantic relations between the words.
A well established way to study the distinct cognitive processes is to repeatedly present the same stimulus. The repeated exposure to a stimulus has been found to be associated with a reduced neural response, called repetition suppression. However, recent findings have also shown that presenting the same stimulus induces enhanced activation in other brain regions called repetition/semantic enhancement. The aim of the current study is to compare the neural correlates associated with the formation of novel semantic meanings with those observed during meaning retrieval of repeated stimuli in order to investigate which brain regions show repetition suppression.
In an fMRI study, 11 subjects read novel and conventional two-word metaphoric expressions and decided whether the expression is meaningful or meaningless. Prior to the study, participants were presented with half of the conventional and half of the novel metaphoric expressions. We found repetition enhancement (for both novel and conventional metaphoric expressions) in the precuneus, left middle temporal gyrus, and left middle frontal gyrus, indicating that these regions were associated with recognition of the previously presented items. More importantly, we found that repeated exposure to novel metaphoric expressions resulted in enhanced brain activation in right supramarginal gyrus and, at the same time, this region demonstrated reduced brain activation for repeatedly presented conventional metaphors. These findings suggest that the right supramarginal area is involved in the formation and the storage of novel semantic relations. This study is important to develop theoretical accounts of the formation of novel conceptual knowledge.