Involvement of default and dorsal attention networks in the episodic remembrance of self-generated thoughts and external elements from real-life events

Episodic memories typically involve records of both external events derived from perceptual processes and internal representations, such as one’s own thoughts and mental states during prior episodes. To date, however, research has mostly focused on the remembrance of stimuli from the external environment, such that little is known about how internal mentation is represented within episodic memory. In the present functional MRI study, we examined the neural correlates of memory for internal thoughts vs external stimuli using a novel method of cuing episodic retrieval from photographs taken by a lifelogging camera during a walk on a university campus. Memories for internal thoughts and external elements were both associated with neural activity in brain areas supporting episodic memory and scene construction processes. Most importantly, however, the two kinds of memories also showed differential activations in large-scale brain networks, with the remembrance of external elements being associated with greater activity in the dorsal attention network, whereas memories of internal thoughts mainly recruited default network areas. Furthermore, functional connectivity analyses revealed that the posterior cingulate cortex can flexibly couple its activity with either dorsal attention or default network areas depending on the kind of memory retrieved. These results provide evidence that focusing on internal or external aspects of prior experience modulates the activity and interaction between large-scale brain networks. They further suggest that the default network contributes to the reinstatement of thoughts experienced during past events, whereas the dorsal attention network supports the allocation of attention to visuo-spatial features within episodic memory representations.