How can we tell when someone has fallen asleep? When do we actually transition from awake to asleep? A new study titled “Tracking the Sleep Onset Process: An Empirical Model of Behavioral and Physiological Dynamics” by scientists at Massachusetts General Hospital suggests that it is not when one falls asleep, but how one falls asleep that matters.
Dr Michael Prerau, Dr Patrick Purdon, and their colleagues combined information from brainwaves, muscle activity and behavior during the sleep onset process (SOP) to track the continuous changes in wakefulness experienced as we fall asleep.
In analyzing the SOP with a subset of healthy subjects the researchers replaced the standard behavioral response task (using sounds that can disturb sleep) with an alternate physiological task (focusing on natural breathing that promotes sleep).
The results turn out to be interesting. By integrating information from both behavioral and physiological changes and modeling them as a continuum over time, the study identified subjects who behaved as though they were awake even though their brains, by current clinical definitions, were asleep. This seems to suggest a natural variation in the way cortical and thalamic networks interact in such people.
Understanding the way we fall asleep is an important problem in sleep medicine, since sleep disorders can impact the process of falling asleep. Ultimately, says Dr Prerau, such methods could greatly improve clinicians’ ability to diagnose sleep disorders and to more precisely measure the effects of sleep drugs.