Free-running sleep

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Free-running in scientific investigation

Free-running sleep experiments can involve any organism which sleeps. Freerunning sleep is sleep which is not adjusted, entrained, to the 24-hour cycle in nature or to any artificial cycle. Such experiments are used in the study of circadian and other rhythms in biology. Subjects are shielded from all time cues, often by a constant light protocol, by a constant dark protokol or by the use of light/dark conditions to which the organism cannot entrain such as the ultrashort protocol of one hour dark and two hours light. Too, limited amounts of food can be made available at short intervals so as to avoid entrainment to mealtimes. Subjects are thus forced to live by their internal circadian "clocks".

The researcher can determine, by observation, the resulting cycles of sleep, activity/alertness, gene-activity, body temperature, blood pressure and/or hormone secretion, for example. The individual's or animal's circadian phase can be known only by the monitoring of some kind of output of the circadian system, the internal "body clock".

When animals or people freerun, experiments can be done to see what sort of signals are effective in entrainment. Also, much work has been done to see how long or short a circadian cycle the different organisms can be entrained to. For example, some animals can be entrained to a 22-hour day, but they can not be entrained to a 20-hour day. In recent studies funded by the U.S. space industry, it has been shown that most humans can be entrained to a 23.5 hour day and to a 24.65 hour day.

The effect of unintended time cues is called masking. If morning rush traffic can be heard from outside, if researchers or maintenance staff appear at the same time each day, an experiment can be ruined by masking.

Intentional free-running

Free-running sleep is sleep that is not regulated in time, used as a form of chronotherapy that can help to cure some sleep disorders^{[citation needed]} in humans. Some people in the industrialised world believe that sleeping naturally involves what they call free-running, but that they cannot afford it due to conflicts with the schedules demanded by work and family. The most typical violations of the principles of intentional free-running sleep are the use of alarm clocks and staying awake past one's accustomed bedtime in spite of drowsiness.

This is different from the way scientists use the term. People who try to free run are generally influenced by daylight and dark and will normally be entrained to the 24-hour cycle in nature.

Free-running sleep as an intention is largely derived from observing non-hibernationary animals, as Max Scheler (GER) and Matthew Fowler (AUST) have both discussed at length in their works. Scheler's references pertain to sleep being used less as a coping necessity, and more as an escape in life of increasing self-awareness. His hypothesis is that a monophasic block of sleep within a certain time-frame, defined by the external environment, so as to allow for specialization in senses, gives evolutionary advantage. An example of this is the adaptation of fruit bats to two sleep blocks of pre-dawn and dusk, to allow for the specialization of their senses, mainly sight and hearing to cope with feeding in their environment.

Fowler’s references to the benefits and costs of free-running sleep on and to society largely centre around the weight the individual holds against that of society. Scheler and Fowler reach contrasting opinions, with Scheler taking a what can be described as a realistic view against Fowler’s impractical, ‘utopian’ mindset.