Navigating our memories: how episodes and space combine in the hippocampal formation

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Spatial and episodic memory are two core forms of memory. Spatial memory allows the formation of a map-like representation of our environment, whereas episodic memory allows remembering specific events of our life. Interestingly, these seemingly different functions rely on the same brain structure: the hippocampal formation. So far, it remains unclear what the relationship between these two forms of memory is and how the hippocampal formation can supports both of these functions. We tested the opposing hypotheses that the hippocampal formation underlies these two systems either via a common coding mechanism or via a parallel processing mechanism. To this end, we combined virtual reality and a life-simulation game with high-resolution fMRI. Our results support different predictions of both hypotheses. On the one hand, our results show that spatial and episodic memory are processed in different modules of the hippocampal formation, as is in line with a parallel processing mechanism. Episodic effects were found in the left, anterior hippocampal formation and spatial effects were found in the right, posterior hippocampal formation. On the other hand, our results point to an interaction between spatial and episodic memory (especially) in the right, intermediate hippocampal formation, in line with a common coding mechanism. We conclude, that spatial and episodic memories are integrated through a pattern completion effect, while features within spatial and within episodic memory become more distinguishable through a pattern separation effect.
Faculteit der Sociale Wetenschappen