Effects of REM sleep deprivation[edit]
REM deprivation causes a significant increase in the number of attempts to
go into REM stage while asleep. On recovery nights, an individual will most
likely move to stage 3 and REM sleep more quickly and experience an REM
rebound, which refers to a great increase in the time spent in REM stage
over normal levels. These findings are consistent with the idea that REM
sleep is biologically necessary.[62][63]
After the deprivation is complete, mild psychological disturbances, such as
anxiety, irritability, hallucinations, and difficulty concentrating may develop
and appetite may increase. There are also positive consequences of REM
deprivation. Some symptoms of depression are found to be suppressed by
REM deprivation; aggression, and eating behavior may increase. [63][64] Higher
noradrenaline is a possible cause of these results. [11] Whether and how long-
term REM deprivation has psychological effects remains a matter of
controversy. Several reports have indicated that REM deprivation increases
aggressive and sexual behavior in laboratory test animals. [63]
It has been suggested that acute REM sleep deprivation can improve certain
types of depression when depression appears to be related to an imbalance
of certain neurotransmitters. Although sleep deprivation in general annoys
most of the population, it has repeatedly been shown to alleviate depression,
albeit temporarily.[65] More than half the individuals who experience this relief
report it to be rendered ineffective after sleeping the following night. Thus,
researchers have devised methods such as altering the sleep schedule for a
span of days following a REM deprivation period [66] and combining sleep-
schedule alterations with pharmacotherapy[67] to prolong this effect. Though
most antidepressants selectively inhibit REM sleep due to their action on
monoamines, this effect decreases after long-term use. Sleep deprivation
stimulates hippocampal neurogenesis much the same as antidepressants,
but whether this effect is driven by REM sleep in particular is unknown. [68]
Animal studies of REM deprivation are markedly different from human
studies. There is evidence that REM sleep deprivation in animals has more
serious consequences than in humans. This may be because the length of
time animals have been REM deprived for is much longer (up to seventy
days) or because the various experimental protocols used have been more
uncomfortable and painful than those for humans. [64] The “flower pot”
method involves placing a laboratory animal above water on a platform so
small that it falls off upon losing muscle tone. The naturally rude awakening
which results may elicit changes in the organism which necessarily exceed
the simple absence of a sleep phase.[69] Another method involves computer
monitoring of brain waves, complete with automatic mechanized shaking of
the cage when the test animal drifts into REM sleep. [70]
Evidence suggests that REM deprivation in rats impairs learning of new
material, but does not affect existing memory. In one study, rats did not
learn to avoid a painful stimulus after REM deprivation as well as they could
before the deprivation. No learning impairments have been found in humans
undergoing one night of REM deprivation. REM deprivation in rats produces
an increase in attempts to enter REM, and after deprivation, REM rebound. In
rats, as well as cats, REM sleep deprivation increased brain excitability (e.g.
electrical amplification of sensory signals), and which lowered the threshold
for waking seizures threshold. This increase in brain excitability seems to be
similar in humans. One study also found a decrease in hindbrain sensory
excitability. The hindbrain was less receptive overall to information in the
afferent pathway, because of the increase in the amplification of those
pathways that it is receptive to.[64]
REM sleep occurs in all land mammals as well as in birds. Amount of REM
sleep and cycling time vary among animals; predators enjoy more REM sleep
than prey.[11] Larger animals also tend to stay in REM for longer, possibly
because higher thermal inertia of their brains and bodies allows them to
tolerate longer suspension of thermoregulation. [72] The period (full cycle of
REM and non-REM) lasts for about 90 minutes in humans, 22 minutes in cats,
and 12 minutes in rats.[73]
In utero, mammals spend more than half (50–80%) of a 24-hour day in REM
sleep.[1
Hypotheses about the function(s) of REM sleep[edit]
While the function of REM sleep is not well understood, several theories have
been proposed.
Memory[edit]
Sleep in general seems to aid memory. REM sleep may favor the
preservation of certain types of memories: specifically, procedural memory,
spatial memory, and emotional memory. REM sleep seems to increase
following intensive learning in rats, especially several hours after, and
sometimes for multiple nights after. Experimental REM deprivation has
sometimes inhibited memory consolidation, especially regarding complex
processes (e.g., how to escape from an elaborate maze). [74] In humans, the
best evidence for REMS improvement of memory pertains to learning of
procedures—new ways of moving the body (such as trampoline jumping),
and new techniques of problem solving. REM deprivation seemed to impair
declarative (i.e., factual) memory only in more complex cases, such as
memories of longer stories.[75] REM sleep apparently counteracts attempts to
suppress certain thoughts.[51]
