Effects of Early Experiences On Behavioral Development: An Experimental Study Based on an "Human-Rat Interaction Paradigm""
Authors: Yin Bin , Wu Xiaorui , Yu Delin 
Published: June 2021

Cultivating the next generation of sound emotional, cognitive and socio-behavioral development is fundamental to human civilization, and the impact of early experiences cannot be ignored from the point of view of probabilistic epigenesis. This study aims to investigate the causal relationship between early experiences and later behavioral development based on a novel experimental model termed the “human-rat interaction paradigm” (HRIP).Thirty-six one-month-old male Sprague-Dawley rats were selected as subjects. Based on the HRIP, three groups (Positive early experiences (PEE) / Negative early experiences (NEE) / Control) were intervened for 3 weeks, and the effects of the manipulation of early experiences on behavioral development were tested through a battery of behavioral paradigms. The results showed that: 1) During the emotional behavior tests, compared with the other two groups, the PEE group was more active in the open arm of the O-maze, more active in the center area of the open field, ate faster in the new and familiar environment, and had less hesitation to adapt to and utilize the new learning device. 2) During the learning behavior tests, the PEE group showed most rule-breaking exploratory behavior in the integrated-learning maze; while the majority of the NEE group learned to open the gate during the early stage of procedural learning, the firmness of their long-term memory was the lowest during the new object recognition task; the control group was overall passive during the whole series of learning behavior tests. 3) During the social behavior tests, the PEE group showed the most interests towards the toy rat, while the NEE group showed the most aversion towards the toy rat. At the same time, while all groups preferred a real rat to a toy rat, only the intervention groups (both PEE and NEE) showed clear preference in interacting with a real stranger rat to a real familiar rat. Moreover, during the empathy and pro-social behavioral tests, when there were no food rewards, all three groups of rats generally would open the gate to rescue the entrapped rat, and after multiple trials their latency to rescue became shorter and shorter; however, when there were food rewards to be shared with the entrapped rat, both the PEE and NEE groups were less likely to open the gate, and after multiple trials, their latency to rescue became longer and longer. When the entrapped rat was unable to reach the food reward without the subject’s active sharing, the NEE group showed much more frequent behavior of feeding interruption and vigilant sniffing, possibly for fear of losing the food to the entrapped rat. 4) During the social competition tests, when there were no food rewards in the tube test, the control group had the highest success rate; when there were food rewards to be competed for, the PEE group had the highest success rate. At the same time, the degree of social rank differentiation was smallest in the control group and largest in the PEE group. The NEE group showed clear differentiation between the high-rank individual and the middle/low-ranked individual. The success rate of the NEE group was overall the lowest during the inter-group social competition tests. We arrived at the following conclusions: 1) On the long run, the early experience intervention based on the HRIP will have sustained and stable effects on the behavioral development. 2) Rich early experiences can improve the sensitivity to learning and social rules. Lack of early experiences can passivate learning and social behavior. 3) Positive early experience can promote the individual to have more interests in exploring "objects", produce more rule-breaking exploratory behavior and maintain the stability of goal behavior; in contrast, negative early experience can cause excessive arousal of negative emotions, inhibit exploration and interfere with the maintenance of goal behavior.