Specifying the core network supporting episodic simulation and episodic memory by activation likelihood estimation

Abstract

It has been suggested that the simulation of hypothetical episodes and the recollection of past episodes are supported by fundamentally the same set of brain regions. The present article specifies this core network via Activation Likelihood Estimation (ALE). Specifically, a first meta-analysis revealed joint engagement of expected core-network regions during episodic memory and episodic simulation. These include parts of the medial surface, the hippocampus and parahippocampal cortex within the medial temporal lobes, and the temporal and inferior posterior parietal cortices on the lateral surface. Both capacities also jointly recruited additional regions such as parts of the bilateral dorsolateral prefrontal cortex. All of these core regions overlapped with the default network. Moreover, it has further been suggested that episodic simulation may require a stronger engagement of some of the core network's nodes as well as the recruitment of additional brain regions supporting control functions. A second ALE meta-analysis indeed identified such regions that were consistently more strongly engaged during episodic simulation than episodic memory. These comprised the core-network clusters located in the left dorsolateral prefrontal cortex and posterior inferior parietal lobe and other structures distributed broadly across the default and fronto-parietal control networks. Together, the analyses determine the set of brain regions that allow us to experience past and hypothetical episodes, thus providing an important foundation for studying the regions' specialized contributions and interactions.

Keywords: Core network; Episodic future thinking; Episodic memory; Episodic simulation; Functional MRI; Meta analysis.

Figure 1

Peak coordinates of all contrasts reporting (A) joint activation for episodic simulation and episodic memory and (B) greater activation for episodic simulation than episodic memory. Blue markers identify studies examining simulations of future episodes, orange of fictitious events, and red include counterfactual episodes.

Figure 2

(A) Results of the ALE meta-analysis identifying the core network, i.e., regions showing consistent engagement during both, various forms of episodic simulation and episodic memory, and (B) results of the complementary analysis revealing regions showing consistently greater activation during simulation than during memory retrieval. Thresholded at p < 0.05, cluster-level corrected.

Figure 3

Results of the meta-analyses revealing (A) common activation during episodic simulation and episodic memory and (B) greater activation during simulation than memory. Thresholded at p < 0.05, cluster-level corrected. Black dashed lines indicate the borders of the default network, and white dashed lines of the fronto-parietal control network as demarcated by Yeo et al. (2011).

Figure 4

Conjunction analysis identifying regions that were significant in both meta-analyses, i.e., part of the core network and exhibiting greater activation for episodic simulation than episodic memory.