Re-membering: spontaneous reactivation of motor cortex during memory re-experiencing

Episodic autobiographical memory (EAM) relies on reactivations of cortical regions engaged during event encoding. While reinstatement of sensory regions is well documented, the role of internal signals from the person's body has received less attention. Here, we investigated whether motor representations from encoding, which are self-generated and ubiquitous in everyday experience, are reinstated at retrieval. Using mixed-reality, participants encoded lifelike episodes involving specific motor actions. The next day, they freely retrieved these episodes while undergoing fMRI (N=30) or EMG (N=23). fMRI results revealed lateralized, effector-specific reactivation in primary and supplementary motor cortices. Moreover, hippocampal-motor connectivity increased during retrieval, and activity in premotor and supplementary motor areas scaled with subjective re-experiencing ratings. EMG recordings extended these findings showing, during retrieval, sub-threshold activation of the muscle active during encoding. These results provide evidence for cortical and peripheral motor reinstatement during the re-experiencing of past events, emphasizing the embodied nature of EAM.