Disentangling developmental effects of play aspects in rat rough-and-tumble play

Animal play encompasses a variety of aspects, with kinematic and social
aspects being particularly prevalent in mammalian play behaviour. While
the developmental effects of play have been increasingly documented in
recent decades, understanding the specific contributions of different play
aspects remains crucial to understand the function and evolutionary
benefit of animal play. In our study, developing male rats were exposed to
rough-and-tumble (RT) play selectively reduced in either the kinematic or
the social aspect. We then assessed the developmental effects of reduced
play on their appraisal of standardised human-rat play
('tickling') by examining their emission of 50-kHz ultrasonic
vocalisations (USVs). Using a deep learning framework, we efficiently
classified five subtypes of these USV across six behaviour states. Our
results revealed that rats lacking the kinematic aspect in play emitted
fewer USVs during tactile contacts by human and generally produced fewer
USVs of positive valence compared to control rats. Rats lacking the social
aspect did not differ from the control and the kinematically reduced
group. These results indicate aspects of play have different developmental
effects, underscoring the need for researchers to further disentangle how
each aspect affects animals.

动物游戏行为涵盖多个维度，其中运动学（kinematic）与社交维度在哺乳动物的游戏行为中尤为普遍。尽管近数十年来，有关游戏行为对个体发育影响的研究报道日益增多，但明确不同游戏维度的具体贡献，仍是阐明动物游戏行为的功能与进化优势的核心要点。本研究中，我们对幼年雄性大鼠开展了针对性干预：选择性削弱其打闹（rough-and-tumble, RT）游戏的运动学或社交维度。随后，通过检测大鼠发出的50千赫兹超声发声（ultrasonic vocalisations, USVs），我们评估了游戏行为削弱对其感知标准化人-鼠互动游戏（“挠痒”）的发育影响。我们借助深度学习框架，高效完成了六种行为状态下五类超声发声亚型的分类工作。研究结果显示：相较于对照组大鼠，游戏中运动学维度被削弱的大鼠在人类触觉接触期间发出的超声发声更少，且整体产生的正效价超声发声数量也显著更低。而社交维度被削弱的大鼠，其超声发声表现与对照组及运动学维度被削弱的大鼠均无显著差异。上述结果表明，游戏的不同维度对动物发育具有差异化影响，这也凸显了研究者需进一步厘清各维度如何作用于动物个体的必要性。