Wiesner Christian D, Davoli Valentia, Schürger David, Prehn-Kristensen Alexander, Baving Lioba
Department of Clinical Psychology and Psychotherapy, Institute of Psychology, Christian-Albrechts-University zu Kiel, Kiel, Germany.
Department of Child and Adolescent Psychiatry and Psychotherapy, School of Medicine, Christian-Albrechts-University zu Kiel, Kiel, Germany.
Front Hum Neurosci. 2018 Jan 10;11:648. doi: 10.3389/fnhum.2017.00648. eCollection 2017.
Sleep helps to protect and renew hippocampus-dependent declarative learning. Less is known about forms of learning that mainly engage the dopaminergic reward system. Animal studies showed that exogenous melatonin modulates the responses of the dopaminergic reward system and acts as a neuroprotectant promoting memory. In humans, melatonin is mainly secreted in darkness during evening hours supporting sleep. In this study, we investigate the effects of a short period of daytime sleep (nap) and endogenous melatonin on reward learning. Twenty-seven healthy, adult students took part in an experiment, either taking a 90-min afternoon nap or watching videos (within-subject design). Before and after the sleep vs. wake interval, saliva melatonin levels and reward learning were measured, and in the nap condition, a polysomnogram was obtained. Reward learning was assessed using a two-alternative probabilistic reinforcement-learning task. Sleep itself and subjective arousal or valence had no significant effects on reward learning. However, this study showed for the first time that an afternoon nap can elicit a small but significant melatonin response in about 41% of the participants and that the magnitude of the melatonin response predicts subsequent reward learning. Only in melatonin responders did a short nap improve reward learning. The difference between melatonin-responders and non-responders occurred very early during learning indicating that melatonin might have improved working memory rather than reward learning. Future studies should use paradigms differentiating working memory and reward learning to clarify which aspect of human feedback learning might profit from melatonin.
睡眠有助于保护和更新依赖海马体的陈述性学习。对于主要涉及多巴胺能奖赏系统的学习形式，人们了解得较少。动物研究表明，外源性褪黑素可调节多巴胺能奖赏系统的反应，并作为一种促进记忆的神经保护剂发挥作用。在人类中，褪黑素主要在夜间黑暗中分泌以支持睡眠。在本研究中，我们调查了短时间的白天睡眠（午睡）和内源性褪黑素对奖赏学习的影响。27名健康的成年学生参与了一项实验，他们要么进行90分钟的午睡，要么观看视频（自身对照设计）。在睡眠与清醒间隔前后，测量唾液褪黑素水平和奖赏学习情况，并且在午睡条件下，获取多导睡眠图。使用二选一概率强化学习任务评估奖赏学习。睡眠本身以及主观唤醒或效价对奖赏学习没有显著影响。然而，本研究首次表明，午睡能在约41%的参与者中引发微小但显著的褪黑素反应，并且褪黑素反应的幅度可预测随后的奖赏学习。只有在褪黑素反应者中，短暂午睡才会改善奖赏学习。褪黑素反应者与非反应者之间的差异在学习过程中很早就出现了，这表明褪黑素可能改善了工作记忆而非奖赏学习。未来的研究应该使用区分工作记忆和奖赏学习的范式，以阐明人类反馈学习的哪个方面可能受益于褪黑素。
