retrieval, only the hippocampus (and other parts of the MTL) acted as a hub during both spatial and temporal order processing. The importance of the hippocampus to spatiotemporal memory is consistent with numerous studies using human neuroimaging643, intracranial EEG recordings14, human lesion24, rat electrophysiological studies44, and rat lesion studies45 suggesting its role in both spatial and temporal components of episodic memory. Thus, one possible interpretation of our results demonstrating important roles for the prefrontal cortex, precuneus, and visual cortex in episodic memory retrieval is that these areas likely facilitate and augment memory trace retrieval4647. One proposal, consistent with past work, is that prefrontal cortex and parietal cortex may be playing more auxiliary roles in memory, such as in executive or attentional processes3742, with visual cortex supporting the visually-rich details that often accompany memory retrieval48. These more auxiliary roles are supported by the comparatively lower levels of connectivity they showed in contrast to the hippocampus in our study. By employing graph theory and functional connectivity in combination, future studies explicitly manipulating these variables, or meta-analyses of past studies, will be better able to address these possible specific roles.
