Uncovering The Mechanistic Differences And Similarities In Episodic Recollection Between Human And Rhesus Macaques

We applied a variant of a classic temporal order judgment paradigm,using a crossspecies comparative approach,to study the retrieval mechanisms of episodic memory in human subjects and rhesus monkeys,uncovering the mechanistic differences and similarities in episodic recollection between human and rhesus macaques.The results support the existence of a hypothetical hierarchy structure of episodic memory during the retrieval stage in both primate species.We observe that if two events happened in two different places,they will be organized in two different and independent segments/groups in the same level of the hierarchy structure.If two events happened in the same place or context,they will be organized linearly in the same segment/group,based on the temporal order of them.When two events which happen in two different places are being distinguished,only the first level in which the segment locates needs to be searched.When two events happening in the same place are being discriminated,the search itself needs to be extended further down to a deeper layer of the organization.These patterns of results highlight that spatial information is the key element in such an organization in both human and rhesus monkeys.In the humans,it is the relative temporal similarity but not the absolute temporal distance between two events that determines the difficulty of discriminating the temporal information between two events.For the rhesus monkeys,although such an organization is also searched,their search efficiency,accuracy and even the mechanism are different from that of the humans.Moreover,during the temporal judgment,not only the temporal information but also the inference based on the external cues of two events are involved in the discrimination.The closer the two events is temporally,the less impact that the inference exerts on the temporal judgment.The results also reveal that the rhesus monkeys may possess a very stable and high volume long-term memory,which may be the key base of the existence of episodic memory ability akin to those in the humans.The circumstantial evidence of the ‘Conscious Recollection' in rhesus monkeys is also gathered in the current study.However due to the differences in the cognitive ability between human beings and rhesus monkeys,the current animal model is yet to be able to fully represent the episodic memory processes in the humans.