How Mental Concepts Shape Sleep: Introducing the Mental Concept Reactivation Hypothesis of Sleep

Sleep problems affect a substantial proportion of individuals, and negative thoughts, rumination, and worry are considered key factors underlying persistence and severity. While extensive research has examined how these states disrupt sleep before falling asleep, much less is known about how mental concepts, including thoughts, expectations, intentions, and emotions, continue to influence sleep during sleep itself. Likewise, the potential benefits of sleep-promoting mental concepts during sleep remain underexplored. Here, we propose the Mental Concept Reactivation (MCR)-Hypothesis of Sleep, suggesting that mental concepts activated before sleep continue to influence sleep by spontaneous reactivations during sleep. Drawing on appraisal theories of emotion and evidence for endogenous memory reactivation, the hypothesis rests on three core premises. First, mental concepts relevant to sleep are activated during the day and particularly before bedtime. Second, these pre-sleep appraisals undergo spontaneous reactivations during sleep, with the intensity depending on their self-relevance. Third, these reactivations affect subjective restoration and objective sleep parameters. We present research supporting our hypothesis, particularly focusing on studies from our lab that began to systematically test key aspects of the MCR-Hypothesis and discuss limitations, alternative explanations, and open questions. Overall, the MCR-Hypothesis offers a testable framework for understanding how cognitive and emotional mental concepts influence sleep during this state. It may help to explain interindividual differences in sleep reactivity to stress, worry, and pre-sleep expectations. It offers a theoretical basis for developing non-pharmacological interventions aimed at reducing maladaptive mental concepts and strengthening beneficial ones, enhancing sleep quality in both clinical and non-clinical populations.