Human-Like Time-Compressed Forward Replay of Video Episodes in Macaque Monkeys

Humans can perform episodic memory replay dynamically by replaying fragments of fine-grained temporal patterns of events and skipping flexibly across subevents. Here, we demonstrate a similar effect in macaque monkeys. We report evidence that the monkeys apply a time-compressed, forward replay mechanism during their judgement the order of cinematic events. We trained six macaque monkeys with a temporal order judgement (TOJ) task and collected 5000 TOJ trials with naturalistic videos. In each trial, they watched a video of about 10 s comprising two across-context clips, and after a 2-s retention delay, performed a temporal order judgement between two frames extracted from the video. The results show that the monkeys adopt a self-terminating search of ordered frames in their mnemonic representation. The memory replay is forward and temporally compressed, paralleling evidence in humans. Such compression of replay is however not sophisticated enough to allow them to skip over irrelevant information by compressing the encoded video globally. Moreover, we also reveal that the monkeys can segment events using contextual boundaries like humans and such contextual segmentation facilitates their memory recall by an increased rate of information accumulation in a drift diffusion model framework. Memory replay is an elaborate mental process and our demonstration of a time-compressed, forward replay mechanism in the macaque monkeys provides insights into mapping the mechanisms and evolution of episodic memory in our lineage.