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.