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

Episodic autobiographical memory (EAM) relies on reactivations of cortical regions, originally engaged during event encoding. While reinstatement of auditory and visual regions during retrieval of external signals is well documented, reinstatement of motor regions, reflecting internal self-related signals from the persons body, remains unexplored. Here, we investigated motor reinstatement at both cortical and peripheral levels. 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 further showed, during retrieval, sub-threshold activation of the muscle active during encoding. Together, these results provide evidence for cortical and peripheral motor reinstatement during the re-experiencing of past events, emphasizing the embodied nature of EAM.