Contemporary models of episodic memory posit that remembering involves the reenactment of encoding processes. Although encoding-retrieval similarity (ERS) has been consistently reported and linked to memory success, the nature of neural pattern reinstatement is poorly understood. Using high-resolution fMRI on human subjects, our results obtained clear evidence for item-specific pattern reinstatement in the frontoparietal cortex (FPC), even when the encoding-retrieval pairs shared no perceptual similarity. No item-specific pattern reinstatement was found in the ventral visual cortex (VVC). Importantly, the brain regions and voxels carrying item-specific representation differed significantly between encoding and retrieval, and the item-specificity for ERS was smaller than that for encoding or retrieval, suggesting different nature of representations between encoding and retrieval. Moreover, cross-region representational similarity analysis suggests that the encoded representation in the VVC was reinstated in the FPC during retrieval. Taken together, these results suggest that in addition to reinstatement of the originally encoded pattern in the brain regions that perform encoding processes, retrieval may also involve the reinstatement of a transformed representation of the encoded information. These results emphasize the constructive nature of memory retrieval that helps to serve important adaptive functions.
Episodic memory enables humans to vividly re-experience past events, yet how this is achieved at the neural level is barely understood. A long-standing hypothesis posits that memory retrieval involves the faithful reinstatement of encoding-related activity. We tested this hypothesis by comparing the neural representations during encoding and retrieval. We found strong pattern reinstatement in the frontoparietal cortex, but not in the ventral visual cortex that represents visual details. Critically, even within the same brain regions, the nature of representation during retrieval was qualitatively different than that during encoding. These results suggest that memory retrieval is not a faithful replay of past event, but rather involves additional constructive processes to serve adaptive functions.
The authors declare no competing financial interests.
We would like to thank Tianyi Tian and Dingxin Wang for developing the fMRI acquisition sequence. This work was sponsored by the National Natural Science Foundation of China (31130025), the 973 Program (2014CB846102), the 111 Project (B07008), and the NSFC project (31521063).