Using Imagination to Understand the Neural Basis of Episodic Memory

TLDR

Functional MRI studies of episodic memory recall and future thinking have identified a consistent brain network, yet little is known about how individual regions contribute to recollection, including roles in self‑schema, familiarity, and distinguishing real from imagined memories. The study used a novel fMRI paradigm in which participants imagined fictitious experiences to investigate neural contributions to episodic memory. The authors employed this paradigm, which elicits experiences that are less temporally oriented and less self‑referential than future‑thinking tasks. They found that scene construction—generating, maintaining, and visualizing complex spatial contexts—underlies both episodic memory and imagination of fictitious experiences, engaging a distributed network including hippocampus, parahippocampal gyrus, and retrosplenial cortex, while episodic‑memory‑specific activity was localized to anterior medial prefrontal, posterior cingulate, and precuneus regions, suggesting that additional task‑specific regions augment the core network for episodic memory.

Abstract

Functional MRI (fMRI) studies investigating the neural basis of episodic memory recall, and the related task of thinking about plausible personal future events, have revealed a consistent network of associated brain regions. Surprisingly little, however, is understood about the contributions individual brain areas make to the overall recollective experience. To examine this, we used a novel fMRI paradigm in which subjects had to imagine fictitious experiences. In contrast to future thinking, this results in experiences that are not explicitly temporal in nature or as reliant on self-processing. By using previously imagined fictitious experiences as a comparison for episodic memories, we identified the neural basis of a key process engaged in common, namely scene construction, involving the generation, maintenance and visualization of complex spatial contexts. This was associated with activations in a distributed network, including hippocampus, parahippocampal gyrus, and retrosplenial cortex. Importantly, we disambiguated these common effects from episodic memory-specific responses in anterior medial prefrontal cortex, posterior cingulate cortex and precuneus. These latter regions may support self-schema and familiarity processes, and contribute to the brain's ability to distinguish real from imaginary memories. We conclude that scene construction constitutes a common process underlying episodic memory and imagination of fictitious experiences, and suggest it may partially account for the similar brain networks implicated in navigation, episodic future thinking, and the default mode. We suggest that additional brain regions are co-opted into this core network in a task-specific manner to support functions such as episodic memory that may have additional requirements.