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Zusammenfassung:
The occurrence of a contextually novel event elicits a cascade of neural responses that results in orienting of attention and enhanced memory encoding (the “von Restorff effect”). Here we used fMRI to identify the neural mechanisms of the von Restorff effect during encoding and retrieval. During the encoding phase, subjects made pleasantness judgments on pictures of faces and houses. In each encoding block, the majority of items were of one stimulus type (standard; e.g. house), and a minority of items were of the other stimulus type (novel; e.g. face). Across blocks, an equivalent number of faces and houses were shown as novels and as standards. Each encoding block was followed by a test block in which subjects were shown equal numbers of studied pictures from the novel and standard categories, as well as previously unseen houses and faces. Subjects were required to decide whether each item was old or new, and for items judged old, to decide whether it was recollected or recognized on the basis of familiarity. Behavioral results showed a robust von Restorff effect, as evidenced by increased recollection of novels relative to standards. Analyses of fMRI responses during encoding showed that, relative to standards, contextually novel items elicited enhanced activation in a distributed cortical network including anterior and posterior cingulate, retrosplenial, ventrolateral and dorsolateral prefrontal, and medial and lateral parietal cortices. For novel items, encoding activation in the amygdala, hippocampus, anterior cingulate, and ventrolateral prefrontal cortex was predictive of subsequent recollection. In contrast, for standard items, encoding activation in ventrolateral and dorsolateral prefrontal and inferior temporal cortex was predictive of subsequent recollection. These results suggest that processing within a limbic network including the amygdala, hippocampus, and anterior cingulate cortex mediates enhanced encoding of contextually novel events.
