Predicting the loss of responsiveness when falling asleep in humans

Abrupt and gradual changes in neuronal processing upon falling asleep and awakening

“…Beyond neuronal correlates in specific pathways such as the auditory cortex, what do our findings reveal more generally about falling asleep – is it fundamentally a gradual or abrupt process? While extensive evidence shows that many electrical, physiological and behavioral phenomena change gradually in the span of minutes (Eban-Rothschild et al, 2016; Lacaux et al, 2023; Ogilvie, 2001), some EEG phenomena and specific measures of behavioral responsiveness do show fast temporal dynamics (Ogilvie, 2001; Strauss et al, 2022). We find evidence supporting both of these seemingly contradicting themes.…”

“…These changes lead one to consider falling sleep as an inherently gradual and continuous process, which does not necessarily occur at any single moment (Ogilvie, 2001). On the other hand, measures of behavioral responsiveness, and possibly some EEG phenomena, do change rapidly around sleep onset, possibly at the order of a few seconds (Ogilvie, 2001; Strauss et al, 2022). This raises the question of whether there is a functionally-relevant abrupt binary switch within the extended process of falling asleep.…”

Behavioral and brain responses to verbal stimuli reveal transient periods of cognitive integration of external world in all sleep stages

“…Our results provide compelling evidence that sleeping humans present, in all sleep stages, transient windows of sensory connection with the outside world during which they process external information at a high-cognitive level and are able to exhibit a behavioral response. Until now, behavioral responsiveness had only been demonstrated during some light sub-stages of N1 sleep (sleep onset) 4,15,16 or in some unique individuals during lucid REM sleep 14 . Our findings go further by demonstrating the possibility for behavioral responsiveness to external stimuli across all sleep stages in ordinary sleep in a large group of participants.…”

“…Third, the whole-brain connectivity as assessed with wSMI at theta frequency did not differ between responsive and non-responsive trials in any of the sleep stages. A recent study 15 showed that whole-brain connectivity might not be as relevant as fronto-temporal connectivity when predicting responses in N1 sleep. Our small number of electrodes limits the interpretation of this connectivity metric.…”

“…Obtaining behavioral responses that serve as real-time indicators of subjective reports could allow us to analyze brain dynamics associated with sensory integration in a trial-by-trial manner.Potentially because behavioral responses have long been assumed to be possible only during wakefulness, they are either rejected from the analysis 12 or not collected at all in sleep studies. The rare studies which explicitly attempted to measure behavioral responses in sleeping participants discovered manual behavioral responses during N1 sleep (sleep onset) 4,15,16 , but not in deeper sleep stages. However, the loss of limb muscle tone could mask behavioral responses during consolidated sleep.…”