Alarm threshold

In medicine, the wake-up threshold is the strength of a certain stimulus (for example an acoustic signal) that is necessary to wake a sleeper up.

Awakening threshold and stage of sleep

During non-REM sleep , the ability to react decreases from sleep stage N1 via N2 to N3, deep sleep. In the phasic part of REM sleep , external sensory stimuli are suppressed, so that the wake-up threshold is higher than the tonic part of REM sleep. In the first sleep cycle , the proportion of deep sleep is highest compared to later cycles, but the REM proportion increases towards morning. The wake-up threshold typically rises in the first hour of sleep and then falls. After sleep deprivation, the wake-up threshold increases for one night up to the 6th hour and then decreases again.

Awakening threshold and stimulus

The height of the wake-up threshold is individually different. It depends not only on the stage of sleep, but also on the type of stimulus and associations associated with it. Even complex stimulus patterns are “recognized” and “evaluated” during sleep.

Wake-up stimulus method in sleep research

In sleep research , the term wake-up threshold is associated with attempts to determine the “depth of sleep” from the beginning of research into sleep. The wake-up stimulus method according to Ernst Kohlschütter from 1862 chose the strength of the stimulus, which leads to awakening and is known as the wake-up threshold, as a measure of the depth of sleep. The threshold stimulus strength was equated with the depth of sleep. The strength of the stimuli and thus also the depth of sleep had such an energetic content and was thus precisely defined and quantified.

Kohlschütter's wake-up stimulus method uses a pendulum hammer that hits a thick slate of slate as an acoustic wake-up stimulus. The angle when the pendulum hammer is released and the distance to the ear of the sleeping test person are noted as the signal strength and reactions of the test person are registered according to the observation. At that time, the interval between measurements was chosen to be 30 minutes. The “sleep depth curve” developed by Kohlschütter showed an increasing sleep depth at the beginning of sleep over the period, which, according to the more recent view, corresponds to the first sleep cycle , and a decrease in sleep depth towards morning.

The method was used for decades, although there were drawbacks. A single value is only found by approaching a series of stimuli. Above-threshold stimuli lead to the awakening, although it remains unclear by what amount the stimulus was above-threshold. Subliminal stimuli in quick succession lower the wake-up threshold for the following stimuli. The wake-up stimulus thus changes the process to be measured. Different types of stimulus strength (sound, light, touch) cannot be compared with one another.

In addition, it was also recognized that it is not only a question of the “energy content”, but also the type of stimulus. There was talk of "wet nurse sleep" and "miller sleep". Wet nurse sleep is a temporary change in the sleep behavior of a caregiver of an infant, in which signals emanating from the child, even of weak intensity, wake up the caregiver, while much stronger stimuli from other sources do not yet. In this context, the term miller's sleep alludes to the working conditions of the millers, who were able to sleep when the noise of the working grinder could be heard from afar, but woke up alarmed when this noise ceased. Consequently, the absence of a stimulus can also lead to arousal. In examinations, one cannot be sure that the stimulus used is indifferent to the individual; the same stimulus may have previously had meaning.

The values found by Kohlschütter with relatively few measurements for his sleep depth curves for the wake-up threshold in the typical course of night sleep have meanwhile been analyzed and compared with results from corresponding polysomnographic examinations and largely confirmed.

literature

Ernst Otto Heinrich Kohlschütter: Measurement of the firmness of sleep . In: Journal for rational medicine . Third row, no. 17 , 1863, p. 209-253 . , here online (PDF file, 5.88 MB), accessed on January 29, 2013

Individual evidence

↑ ^a ^b Niels Birbaumer et al .: Biological Psychology . Springer, Heidelberg 2006, ISBN 978-3-540-25460-7 , pp. 560 . , here online , accessed on January 29, 2013.
↑ Johannes Werner: A method for continuous sleep depth measurement in humans with the help of electrencephalo-, electrooculo- and electrocardiography (EEG, EOG and EKG) . In: Journal for all of experimental medicine . Vol. 134, No. 2 , 1961, p. 187-209 , doi : 10.1007 / BF02046290 .
^ Mathias Basner: Arousal threshold determination in 1862: Kohlschütter's Measurements on the Firmness of Sleep . In: Sleep Medicine . Vol. 11, No. 4 , 2010, p. 417-422 , doi : 10.1016 / j.sleep.2009.10.002 (English).

[bir-1] Niels Birbaumer et al .: Biological Psychology . Springer, Heidelberg 2006, ISBN 978-3-540-25460-7 , pp. 560 . , here online , accessed on January 29, 2013.

[Werner1961-2] Johannes Werner: A method for continuous sleep depth measurement in humans with the help of electrencephalo-, electrooculo- and electrocardiography (EEG, EOG and EKG) . In: Journal for all of experimental medicine . Vol. 134, No. 2 , 1961, p. 187-209 , doi : 10.1007 / BF02046290 .

[Basner2010-3] Mathias Basner: Arousal threshold determination in 1862: Kohlschütter's Measurements on the Firmness of Sleep . In: Sleep Medicine . Vol. 11, No. 4 , 2010, p. 417-422 , doi : 10.1016 / j.sleep.2009.10.002 (English).