Rate of context change at encoding influences hippocampal autocorrelation and temporal clustering of free recall
Lindsay I. Rait1 (email@example.com), Guo Wanjia1, Zhifang Ye1, Sarah DuBrow1, Brice A. Kuhl1; 1University of Oregon
Retrieved context models posit that when an item is presented during study, it is stamped into a slowly drifting internal context representation. In humans, this context drift is thought to critically determine how memories are organized during recall—in particular, the tendency to recall items according to the temporal order in which they were encoded (i.e., temporal clustering). While the hippocampus is thought to be essential for encoding contextual information, there is surprisingly little evidence linking hippocampal context representations to temporal clustering in free recall. In an fMRI experiment (n=38), we actively manipulated the rate of context change in order to test whether this produced parallel changes in hippocampal ‘drift’ during encoding and temporal clustering during recall. The context change manipulation consisted of switching background scenes at different switch rates during the encoding of a list of words. Afterwards, subjects freely recalled as many words as possible. While context switch rate had no effect on the total number of words that were recalled, it significantly influenced the degree of temporal clustering in recall. Specifically, temporal clustering was inversely related to switch rate, with the least temporal clustering occurring when switch rate was highest. Strikingly, this qualitative pattern of data was mirrored by autocorrelation (drift) in the hippocampus: autocorrelation significantly decreased when switch rate increased. Collectively, these findings suggest that switching between contexts at a high rate disrupts internal context representations in the hippocampus, thereby weakening temporal clustering during subsequent recall.
Topic Area: LONG-TERM MEMORY: Episodic
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