A new statistical method and behavioral task to get a deeper insight into the point of transition from awake to asleep has been developed by scientists.
Scientists at Massachusetts General Hospital developed the method to track the dynamic process of falling asleep.
Dr Michael Prerau, Dr Patrick Purdon, and their colleagues used the evolution of brain activity, behaviour, and other physiological signals during the sleep onset process to automatically track the continuous changes in wakefulness experienced as a subject falls asleep.
The study suggested that it was not when one falls asleep, but how one falls asleep that matters. Using these methods, the authors quantified a subset of healthy subjects who behaved as though they were awake even though their brains, by current clinical definitions, were asleep.
The researchers replaced a standard measure, the behavioural response task, which uses sounds that can disturb sleep, with a new task centred on a subject's focused natural breathing, an act which might even promote sleep. They modeled the physiological and behavioural changes occurring during sleep onset as a continuum that can develop gradually over time.
The identification of some subjects who continued to perform the task even though current clinical measures would say they were asleep suggests a natural variation in the way cortical and thalamic networks interact in these people.
Dr Prerau said that ultimately, such methods could greatly improve clinicians' ability to diagnose sleep disorders and to more precisely measure the effects of sleep drugs.
The study is published today in PLOS Computational Biology.