Past experience modulates the neural mechanisms of episodic memory formation

Neuroscientists have observed the "birth" of memories, but have not explored how an organism's past experience with materials interacts with the neural mechanisms of episodic memory formation. Using functional neuroimaging, we searched for such an interaction by examining brain activity during memory encoding that predicted participants' subsequent episodic memory for novel and repeated scenes. Memory for both scene types was predicted by a common posterior network in occipital and parietal cortices. Medial temporal memory predictors were modulated by scene repetition: the right anterior hippocampus and right amygdala predicted memory for novel scenes only, whereas posterior hippocampi predicted memory for repeated scenes only. There was also greater functional connectivity between the temporal pole and anterior versus posterior hippocampus, and this link predicted memory for novel but not repeated scenes. In contrast, there was greater functional connectivity between the precuneus and posterior versus anterior hippocampus, and this link predicted memory for repeated but not novel scenes. Together, these results reveal a functional specialization within the hippocampus for the encoding of novel and previously experienced materials, and suggest that the topography of this specialization might be related to local variations in connectivity. Because episodic memory for repeated scenes was superior, our results also support traditional views of encoding emphasizing the role of prior representations, and illuminate one way in which humans use existing memories to help form new ones. In so doing, our results challenge recent novelty-encoding hypotheses.