Types of Sleep Deprivation

Slow Wave Sleep (SWS) Deprivation

    Stage 4 sleep deprivation in humans did not result in an increase number of attempts to enter stage 4.  However, it did result in a significant rebound of stage 4 on a recovery night.  The amount of stage 3 sleep in the above study doubled during nights of stage 4 deprivation.  Stage 4 sleep deprivation has also been shown to produce significant increases in the percentage of stage 2 sleep during the deprivation period, while the percentage of REM remains constant.  These same experimenters observed REM rebound on the second and third night of the recovery period for stage 4 deprivation.

     There is one important confounding variable when depriving human participants of stage 4 or all of slow wave sleep.  These stages of sleep are defined by the presence of delta frequency brain waves (which are very slow, 1-3 Hertz, and of high voltage).  Stage 3 sleep is said to occur when a 30-second EEG epoch consists of 20-50% delta waves.  Stage 4 sleep is said to occur when one EEG epoch is greater than 50% delta waves.  Stages 3 and 4 together are said to constitute slow wave sleep.  The problem with depriving a subject of stages 3, 4 or all of slow wave sleep is that the person is still producing delta waves.  An individual in this situation is not awakened until the delta waves constitute 20% of any given epoch, which means that one can still produce a significant amount of these low frequency, high amplitude brain waves and be said to not have experienced slow wave sleep.  For slow wave sleep deprivation to be effective, the constituents of slow wave sleep (i.e. delta waves) must be eradicated.  In the studies of slow wave sleep deprivation in humans, this has not been achieved to any significant extent due to the definitions of stage 3 and 4 sleep.

    This point is extremely relevant in the study above.  The findings were that during stage 4 sleep deprivation stage 3 sleep increased.  This occurred because the division of stages 3 and 4 sleep is arbitrary.  There was probably not more attempts to enter stage 4 sleep during the deprivation period because the requirement for slow wave sleep as a whole had been met through an increase in stage 3 sleep.  The same effect is likely to occur when slow wave sleep as a whole is removed, because there is still that portion of sleep in which the EEG shows 0-20% delta waves, that is not classified as stage 3 sleep, but shows the one defining characteristic of slow wave sleep.

    Keeping in mind this important potential confound, there has been more research on slow wave sleep deprivation.  One experiment reported no significant changes in mood during SWS deprivation.  All complaints tended to be physical in nature.  These included being “physically uncomfortable…, less aggressive and manifesting concern over vague physical complaints and changes in body feeling."  Another study confirmed these results, and added that the overall impression of a person deprived of stage 4 sleep was that of depression and hypochondriacal feeling.

    Animals deprived of slow wave sleep showed more significant consequences than did humans.  Rats died after several weeks of high-amplitude non-REM sleep deprivation (believed to be analogous to slow wave sleep in humans).  Rats that were deprived of this sleep, but not until death, showed increases in delta and theta waves during rebound sleep, and also a decrease in sleep spindle.


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