Repetitive thinking has been conceptualized as a continuum, ranging from mind wandering to perseverative cognition such as worry and rumination. According to the mind wandering-perseverative cognition continuum hypothesis, mind wandering may be considered as an adaptive brain function that turns into maladaptive (perseverative) when it becomes rigid and inflexible (associated with slower RTs in cognitive control tasks, more effort to inhibit the thought and intrusiveness). Interestingly, behavioral studies show detrimental effects of sleep loss on cognitive control processes. Accordingly, sleep may play a critical role in the pathway from mind wandering to perseverative cognition. Despite this evidence, research conducted so far mostly investigated the effects of repetitive thinking on sleep, and largely ignored the effects of sleep as modulator of repetitive thinking. The aim of this study is to explore the effects of sleep on mind wandering, worry and rumination, their cognitive features (RTs, effort to inhibit the thought and intrusiveness), and their psychophysiological correlates using an experimental sleep deprivation procedure in healthy human beings. 60 participants will be randomly assigned either to a sleep deprivation or a good sleep control condition. The morning after, they will perform a 20-min tracking task with a thought probe. Spontaneous occurrence of mind wandering, worry and rumination episodes during the task will be investigated. Furthermore, psychophysiological measures (electrocardiogram) will be collected during the session. It is hypothesized that participants in the sleep deprivation condition, as compared to those in the good sleep condition will show: 1) lower rates of mind wandering, 2) higher rates of worry and rumination, 3) slower RTs, 4) more effort to inhibit the thought and more intrusiveness of the thought, 5) autonomic rigidity (low heart rate variability).
As briefly shown in the introduction, most of the studies to date explored the relationships between repetitive thinking and sleep under the hypothesis that repetitive thinking had a negative impact on sleep. Instead, the effects of sleep on this kind of cognitions remains unknown. Interestingly, the last two decades of psychophysiological, behavioral, neuropsychological and neuroimaging research suggest that an opposite direction of this relationship (sleep as a modulator of repetitive thinking), is also plausible since sleep is involved in the regulation of cognitive and emotional processing. In fact, experimental studies have shown that sleep modulates the performance on tasks requiring cognitive control abilities such as executive functions (Lim & Dinges, 2010; Ballesio et al. 2018a). Parallel, insufficient sleep has shown to enhance negative and decrease positive emotional experience (Baglioni et al. 2010) and to be associated with poor cognitive strategies of emotion regulation such as cognitive reappraisal (e.g. Mauss et al. 2015). Further indirect evidence supporting a role of sleep in modulating cognitive-emotional processing comes from neuroimaging literature. For example, fMRI studies showed an abnormal functional connectivity between brain areas traditionally associated with emotional reactivity (e.g. the amygdale) and cognitive control processes (e.g. the prefrontal areas) after sleep deprivation (e.g., Yoo et al., 2007). Also, meta-analyses of clinical literature showed the chronic disturbed sleep is longitudinally associated with increased incidence of mood and cognitive disorders such as major depression (Baglioni et al. 2011) and dementia (Shi et al. 2017). Taken together, evidence suggests that in healthy human being, sleep may be involved in modulating the occurrence and intensity of repetitive thinking. To the best of our knowledge, no studies to date examined whether sleep modulates repetitive thinking. Our research represents a first attempt in exploring the influence of sleep in the mind wandering-perseverative cognition pathway. This research encompasses important clinical implications. Disturbed sleep and insomnia are considered predictors of depression (Baglioni et al. 2011). Perseverative cognitions are core maintaining factors of depression. Thus, it is possible that disturbed sleep may lead to depression through enhanced perseverative cognitions. Our study will provide preliminary evidence in this direction. Results of this study may potentially foster interventional studies aiming at improving sleep in at-risk populations with a consequent reduction of perseverative cognition and depression risk. We recently showed preliminary results in this direction. In a pilot randomized controlled trial of cognitive behavioral therapy for insomnia, we showed a significant decrease of ruminative thinking after sleep treatment (Ballesio et al. 2018c).