Episodic memory is based primarily on meaning. This is behaviorally well documented in studies on memory for prose, in which the meaning of novel sentences is typically well remembered but information pertaining to exact wording and syntax is not. The neural basis of this 'verbatim effect' is poorly understood. In the current fMRI study, we manipulated the novelty of sentences at different levels to test whether medial temporal lobe (MTL) regions that are known to play a critical role in verbal episodic encoding would respond preferentially to the novelty of sentence meaning. Fifteen participants were pre-familiarized with auditory sentences describing unique episodes. During scanning, they encountered sentences that were old, that contained a change in (i.e., were novel in terms of) syntactic relationships, that contained a change in semantic relationships, or that described an entirely novel episode. Subsequently, participants performed a recognition memory test for the different types of novel information encountered. Behavioral data confirmed the typical verbatim effect. Analyses of fMRI data revealed differential MTL activation in the left hippocampus and entorhinal cortex with a response profile across conditions that paralleled the behavioral results; the identified region responded selectively to those conditions that contained semantic novelty. Other regions, by contrast, showed a novelty response that did not share this selectivity. Our findings suggest that the verbatim effect can be linked to hippocampally-based novelty-assessment processes that operate based on semantic relationships.
(c) 2008 Wiley-Liss, Inc.