Mind-wandering and Predictive Processes in Narcolepsy: a Putative Mechanism Through Covert REM Intrusions

Mind-wandering and Predictive Processes in Narcolepsy: a Putative Mechanism Through Covert REM Intrusions, the NarcoWandering Study

Mind wandering is a state in which attention turns away from the external environment or current task to focus on internal thoughts (past experiences, future events, planned actions...). Humans are thought to spend at least one third of their waking lives in this state. Mind wandering can be assessed experimentally by investigating mental content during well-controlled tasks. In this case, task-unrelated thoughts likely to arise during tasks of varying cognitive demand are studied. Mind wandering (=task-unrelated thoughts) has a deleterious effect on cognitive performance in most paradigms, particularly those requiring sustained attention and executive control. However, this phenomenon could also have cognitive benefits, although knowledge on this issue remains limited. For example, it has been suggested that mind wandering could promote creativity, anticipation of future scenarios and prospective memory. In a recent behavioural study, we investigated the cost and benefit of mind wandering in an implicit visual-motor probabilistic learning task (ASRT - Alternating Serial Reaction Time Task). ASRT distinguishes between two fundamental processes: visuomotor performance and implicit statistical learning. While the former reflects visuo-spatial discrimination efficiency, the latter refers to the unintentional acquisition of probabilistic regularities of external inputs. Reduced visuo-spatial accuracy and faster but less accurate responses have been observed during periods of mind-wandering. On the other hand, mind-wandering was associated with enhanced statistical learning reflecting improved predictive processing.

Whereas the study of the neural correlates of mind-wandering is constantly growing, the mechanisms triggering mind-wandering are far from being unravelled, but may involve sleep pressure. Thus, the frequency of mind wandering tends to increase after sleep deprivation or during attention-demanding cognitive tasks, during which neurophysiological markers of local sleep appear. These markers of sleep during wakefulness are frequently observed in hypersomnolence disorders. They are generally defined by the appearance of slow waves (typical of slow wave sleep, SWS). Nevertheless, sleep intrusions during wakefulness may not be limited to non-rapid-eye-movement (NREM) sleep but also concern REM sleep. REM sleep is the sleep state when the most intense forms of dreaming occur, and could therefore be phenomenologically similar to the reverie of mind wandering. Thus, daytime mental wandering could be triggered by intrusions of REM sleep during wakefulness.

Patients with narcolepsy type 1 (NT1) exhibit frequent REM sleep onset during daytime wakefulness. The study of ASRT in this population therefore offers a unique opportunity to investigate the role of REM sleep intrusions in mind wandering. The hypothesis is that mind wandering would be observed more frequently during the ASRT task in NT1 patients (with REM sleep intrusions during wakefulness) than in patients with idiopathic hypersomnia (IH) (with NREM sleep intrusions during wakefulness) and patients with subjective hypersomnolence (little or no sleep intrusion). Furthermore, it could be possible that REM sleep-related mind wandering would be associated with impaired visuomotor performance in terms of accuracy, but improved predictive processing (probabilistic learning) compared to NREM sleep intrusions or no sleep intrusion during the task.

Inclusion Criteria:

• Patients with NT1 or IH diagnosis according to ICSD3-TR criteria (American Academy of Sleep, 2023)
• For patient with IH: with abnormal Mean Sleep Latency Test (MSLT) (mean latency ≤ 8 min, ≤ 1 SOREMp)
• Patients with subjective hypersomnolence without underlying cause (negative extensive work-up including actigraphy, PSG, MSLT, 24h bedrest, biological tests, MRI, psychiatric consultation; this allows to rule out sleep deprivation, irregular sleep/wake schedule, sleep apnea or other sleep disorders associated with sleep fragmentation, somatic/psychiatric causes of hypersomnolence, sedative substance intake). This type of "controls" have already been used in studies on hypersomnolence disorders.

Exclusion Criteria:

• Cognitive impairment not compatible with the task
• Treatment with antidepressant
• Other cause of hypersomnolence: untreated severe obstructive sleep apnea, sleep-wake circadian rhythm disorders, sleep deprivation, somatic/psychiatric causes of hypersomnolence, sedative substance intake
• Unstable medical or psychiatric condition
• Refusal to participate