The neural architecture of discourse compression

Re-telling a story is thought to produce a progressive refinement in the mental representation of the discourse. A neuroanatomical substrate for this compression effect, however, has yet to be identified. We used a discourse re-listening task and functional magnetic resonance imaging (fMRI) to identify brain regions responsive to repeated discourse in twenty healthy volunteers. We found a striking difference in the pattern of activation associated with the first and subsequent presentations of the same story relative to rest. The first presentation was associated with a highly significant increase in blood oxygen level dependent (BOLD) signal in a bilateral perisylvian distribution, including auditory cortex. Listening to the same story on subsequent occasions revealed a wider network with activation extending into frontal, parietal, and subcortical structures. When the first and final presentations of the same story were directly compared, significant increments in activation were found in the middle frontal gyrus bilaterally, and the right inferior parietal lobule, suggesting that the spread of activation with re-listening reflected an active neural process over and above that required for comprehension of the text. Within the right inferior parietal region the change in BOLD signal was highly correlated with a behavioural index of discourse compression based in re-telling, providing converging evidence for the role of the right inferior parietal region in the representation of discourse. Our findings demonstrate, for the first time, the existence of a neural network underlying discourse compression, showing that parts of this network are common to re-telling and re-listening effects.