Does REM Sleep Improve Memory?
An Argument Paper for College Students
[authors]
Spring 2010
A Paper for Time Magazine
Introduction
Have you ever wondered why you don’t feel like yourself after a night of no sleep?
Simple tasks such as getting ready for the day are difficult, let alone anything that requires you to
think in depth. School becomes painful, and your brain actually hurts from the complex task of
thinking. As college students, all of us have felt these effects at one time or another, pulling that
all-nighter to get in an extra few hours of studying instead of sleep. Because this is helpful, right?
Actually, those precious few hours of sleep sacrificed could be the difference between an A or a
B, but not the way you might think. This is because researchers have discovered that sleep is
necessary for improving memory, and getting a few hours the night before a test may be much
more beneficial to your memory than getting no sleep.
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Although what goes on when you sleep is
Cycles of sleep stages throughout the night
not entirely known, we all know that not getting
enough leaves us grumpy and mentally crippled.
Most of us have heard of REM sleep, and for
those that haven’t, it’s a stage of sleep where there
is rapid eye movement (REM) and nerves are
firing even though our muscles are not
Sleep can be largely separated into two types; REM
(Rapid Eye Movement) sleep and NREM (nonREM)
sleep, which alternate throughout the night in humans
with an average of 90-minute cycles.
contracting. Researchers are just starting to understand sleep and its effects on human function;
specifically, it appears to have an effect on memory capabilities. Researchers have proven that
non-REM (NREM) sleep, or stages other than REM sleep, definitely improves some memory,
but they also think that REM sleep may play a role in this improvement (see text box to right). In
rodents and humans, studies have found that REM sleep increases during specific time intervals
following training tasks, this increase is followed by an improvement on task performance,
suggesting that REM sleep plays a role in the memory improvement of these tasks (Maquet et al.,
2001).
When most people think about memory, they typically associate it with learning and how
people with a good memory can recall all sorts of things. However, this recall of information is
just one part of memory; you also have memory for how to do things, like riding a bike. This is
because memory is actually a huge concept with many complicated subtypes, so when
researchers refer to an “improvement in memory”, it’s not exactly what you might think. Instead,
what researchers view to be an improvement in memory is actually an improvement in
performance on different tasks designed specifically to test isolated parts of memory. This is
because an improvement in memory will directly result in an improvement on task performance,
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which most of the time you don’t consciously think about. Throughout the rest of this paper,
when we say that sleep improved memory we literally mean that there was an improvement in
the performance of the task. Conversely, whenever we say sleep didn’t improve memory, it
means that there was no performance improvement on the task.
Whether or not REM sleep improves memory is a controversial topic in science, and
there is no definite answer at the present moment. Because this area of science is so complicated
and research is still in the beginning stages, concrete conclusions are difficult to draw. These
difficulties are intensified because memory is very complex, and only when it is broken down
and studied in smaller components can it begin to be understood. These factors led us to ask the
question, does REM sleep improve memory?
Oftentimes, studies done in science on the same topic reach completely different
conclusions, even when they use the same general experiments and procedures. The topic of
sleep and memory is no exception. We analyzed eight studies spanning from 1994 to as recent as
2009, and two reviews that looked at eighty studies over the span of thirty years, all of which
address the question of whether or not REM sleep improves memory. We chose these main eight
studies based on the fact that they all had varying characteristics, each one giving a unique
perspective on the topic of sleep and memory. These studies also had a broad range of tasks,
which we categorized into three main types. We will later address why the difference between
these categories is relevant and important, under the Whether or Not REM Sleep Improves
Memory Is Determined By The Type of Task section. Out of the studies we analyzed, four
concluded that REM sleep improved memory, three found no improvement, and one had mixed
results showing both (Figure 1).
Because these eight studies were all done on the topic of sleep and memory, there were
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some basic methods that were used by all of them. The
Man Having an EEG Performed
experiment always took place in a sleep lab, which was
specifically set up to test the researcher’s hypothesis.
The subjects used in the studies were all humans, both
male and female, typically chosen to be in the age
range of 19-35 years old because this is when sleep
patterns are the most normal. They were separated into
different groups, which were randomly assigned to be
either a group getting some kind of sleep (Full night,
only SWS, or only REM), or they were
assigned to the wake group to serve as
a control (see middle right text box).
The brain, during both wake and sleep states,
constantly produces electrical wave impulses
as a result of its activity. A measurement tool
used to produce a visual representation of
these wave impulses is known as an
electroencephalogram (EEG), which
measures this activity while a subject sleeps.
The electrodes then transmit the wave type
onto a screen, which the researchers can
interpret to determine the stage of sleep the
person is in.
Controls: When researchers perform an experiment with the
purpose of determining the effect of a single variable of interest (in our
case sleep is the variable) on a particular system (for us it is memory),
they use a scientific control to minimize the unintended influence of
other variables on the same system. These outside variables can
include researcher bias, environmental changes, and biological
variation. Scientific controls ensure that the data is valid.
Of the groups assigned to get some kind of sleep other
than a full night’s sleep (only SWS or only REM), a
Wave Types From an EEG
During Different Sleep Stages
deprivation method was usually used. For example, if a
subject was in a group only getting SWS, then he or she
would be deprived of REM sleep. Any time the EEG
showed waves characteristic of REM the subject would
be woken up (see top and bottom text boxes to right).
This arousal is actually something researchers feel is
controversial, and we will explain the effects of this in
the section labeled Reasons Why Somebody Might Argue
NREM sleep consists of 4 stages, the
deepest being stages 3 and 4 which are
typically referred to as “slow wave sleep”
or SWS because of the large-amplitude,
low-frequency waves these stages display
on the EEG. Conversely, REM sleep as
well as stage 1 & 2 are characterized by
low-amplitude, relatively fast waves on an
EEG.
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REM Sleep Does Not Improve Memory. In addition, in order to be sure the subjects were
accustomed to sleeping in the conditions of the sleep lab, they were acclimated to the
environment by spending a night or two in the lab before any training or testing took place. The
researchers did this to be sure that the results they got were not affected by other factors, such as
stress of a completely new sleep environment. The subjects, after acclimating to the
environment, were typically trained on a task in the evening, allowed to get some type of sleep
(whichever group they were assigned to), and then tested for performance upon waking. When
the researchers observed improvements after sleep, they could only assume that these
improvements came from the sleep itself because that was the only thing that had taken place
between the training and the testing.
Even though these studies have the same basic methodology, when they are looked at in
closer detail, some underlying characteristics become noticeable that seem to predict whether or
not REM sleep will indeed improve memory. Based on this, we decided that the main reason
researchers have found conflicting data on whether REM sleep improves memory is a direct
result of the type of task the study used. Because of this, we will argue that REM sleep improves
memory only if the task has a cognitive aspect; REM sleep will not improve memory if the task
is purely motor.
Whether or Not REM Sleep Improves Memory Is Determined By The Type of Task
The most important reason that determines whether or not REM sleep will improve
memory is the type of task a subject is asked to perform. If you look at Figure 1, you will see that
all of the studies that found that REM sleep does not improve memory used tasks that were
purely motor. On the other hand, all of the studies that found that REM sleep does improve
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memory used tasks that were purely cognitive or a mix of both. There is no other major
difference in the experimental methods or procedures across studies that can account for these
discrepancies in findings. Instead, these differences can be accounted for by the fact that
different studies simply used different types of tasks to test for an improvement in memory.
Purely motor tasks are one type of task some studies used to test if REM sleep improved
memory. This is a task that does not need any help from conscious thought to produce the
movements needed to complete the task. Consider when you move your arm to grab something;
you don’t have to consciously think about the
movements. You just do it. It’s the same in a purely
motor task and three of the studies we looked at used
tasks of this nature (Figure 1). Cai and Rickard
(2009) used a sequential finger-tapping task in their
study, in which the subjects were asked to repeatedly
tap a sequence with their left hand. In order to rule
out any cognitive aspect, this sequence was shown
Map of the movements subjects were
asked to make using the robotic arm in
the study done by Donchin et al. (2002)
on the top of the screen at all times, ensuring that the
task was purely motor. Donchin et al. (2002) also used a purely motor task, in which the subjects
were asked to move a robotic arm from a starting point to an end point, in varying force fields (in
ones that were harder to move, and in ones that were easier). This movement requires no higherlevel cognitive input, and so again, it was purely motor (See right text box). Lastly, Smith and
Macneill (1994) used a task called the pursuit rotor task, which is purely motor in nature. In this
task subjects were asked to follow a light moving in a rectangular shape with the tip of a pointer,
which required no cognitive component to complete. This is because the task had very short-
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duration training sessions and could be explained to the subjects in about two minutes, indicating
to the researchers that there was no need for higher cognitive thought. If it did have a cognitive
component, it would take much longer for the subject to understand it. It is important to note that
these three studies are also the ones that did not see any improvement after REM sleep,
suggesting that REM sleep plays no role in the improvement of memory for a purely motor task.
The other two types of tasks used by these studies to determine if REM sleep improved
memory were purely cognitive tasks or tasks with a mix of motor and cognitive, both of which
include a cognitive aspect. One that is purely cognitive will rely only on conscious thought to
successfully complete the task, like the one used by Hupbach et al. (2009); this required infants
to recognize an artificial language of three-word strings that mimicked word patterns in the
English language (Figure 1). Because there is no motor component to this, it is purely cognitive.
Lastly, a task that is a combination of both will have two components; one that is the conscious
thought that makes the correct decision to produce the second component, an accurate motor
movement. The study done by Plihal & Born (1997) required subjects to master a mirror-tracing
task. Because this task included both the movement for tracing various shapes and the conscious
effort to make correct mirrored movements, it can be classified as a task involving both motor
and cognitive aspects. In all the remaining studies we analyzed (Maquet et al., 2001; Karni et al.,
1994; and Gais et al., 2000), the type of task used was a visual-motor task in which there was
either a stimulus and a timed response, or the recognition of a specific pattern (texture
discrimination). These tasks were also a mix of cognitive and motor; the visual perception was
the cognitive component, and the response was the motor component. Because all of these
studies used tasks with a cognitive component, it should be noted that they all concluded that
REM sleep did improve memory, with the exception of Gais et al. (2000), which had mixed
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results and only partially concluded that REM sleep improved memory.
The results of the studies using tasks that included a cognitive aspect are not quite as
clear as the ones using a purely motor task. We classified the results of the study done by Gais et
al. (2000) as “mixed results” because their study did find an improvement to memory but the
improvement was conditional. They divided the subjects in their experiment into three main
groups: one group was allowed to get a full night of sleep, one was only allowed to get slow
wave sleep (SWS), and the last group was only allowed to get REM sleep. When they tested the
subjects after their night of full sleep, SWS, or REM sleep, the results they found were
unexpected; the subjects that were allowed to only get REM sleep did not improve on the task at
all, which is opposite of the researcher’s original prediction that REM sleep would cause an
improvement. Subjects that were only allowed SWS improved on the task, but the subjects that
were allowed to get the full night of sleep (both SWS and REM) showed a three times greater
improvement than those that only got SWS. The researchers interpreted these results to suggest a
“two-step consolidation process” in which the improvement began during SWS, and was greatly
improved by REM sleep (Gais et al. 2000). The group that was only allowed REM sleep showed
no improvement because SWS was needed to start this improvement process, and this group
lacked this. However, the fact that the full night of sleep group improved by three times as much
as the only SWS group proves that REM sleep is still crucial for memory improvement.
Although Gais et al. (2000) found conditional results on whether or not REM sleep
improved memory, it is only one out of the five studies that used tasks with a cognitive
component. Four additional studies that also had a cognitive component showed a definite
improvement in memory with REM sleep alone (Maquet et al., 2001; Hupbach et al., 2009;
Plihal and Born 1997). Because of the shear volume of 4 to 1, we still conclude that REM sleep
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plays a role in some aspect of memory improvement.
The Reactivation of Brain Areas is Evidence that REM Sleep Improves Memory When the
Task Has a Cognitive Component
It has also been shown that REM sleep plays a role in the improvement of memory of
tasks with a cognitive component
through the reactivation of brain areas
Regional Cerebral Blood Flow (rCBF) During Wakefulness
and REM Sleep
during REM sleep. In Maquet et al.
(2000), researchers found that brain
areas activated while a subject was
performing a task were then
Figure 2. This image shows that the areas activated during the learning of
the task were reactivated later during REM sleep. This implicates a role for
sleep in memory improvement of a mixed task (both motor and cognitive)
reactivated again during REM sleep
(Figure 2). After the subjects were allowed to have REM sleep, their performance (measured by
reaction times) on the stimulus-response task significantly improved by 24%, which was enough
for the researchers to classify as a significant improvement
(Figure 3). Because the same brain areas were active during
Reaction times during
different testing sessions
the execution of the task as well as during REM sleep, it is an
indicator that some part of the task was being processed
during this stage of sleep. This implies that it is indeed REM
Figure 3. Reaction time of a trained
sleep that is responsible for the improvement in reaction
task improved after REM sleep
(improvement seen in Session C),
indicating REM sleep improves
memory consolidation
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times, and therefore the reason for the improvement in memory for the task.
REM Sleep Helps People Learn a New Task, But Not One They Already Know How to Do
Yet another study that used a task that was mixed motor and cognitive also supports the
idea that REM sleep is necessary to see an improvement in memory. In the study done by Karni
et al. (1994) subjects were tested on two tasks; one was a newly learned task, like those used in
our other studies, and one was a previously learned task, which served as a control. When tested
on the new task, the researchers found that the subject’s performance improved after a night of
normal sleep, but when they were deprived of REM sleep (REMD), no improvement was seen.
Before the researchers could be sure that the improvement on the task was due to REM sleep
they had to rule out SWS as being the part of sleep responsible for the improvement because the
subjects went through both SWS and REM during their night of normal sleep. When the subjects
were deprived of SWS they still showed significant improvements on new task performance,
which strongly implicated REM sleep as being responsible for this improvement. Because if
SWS was responsible they would not of observed task improvement in the subjects after they
were deprived of SWS. Lastly the researchers tested the subject’s performance on the previously
learned control task after a night of REMD, which resulted in no effect on their performance.
REM sleep only improved the new task because it was still in a “fragile” state of learning
whereas the control task was fully protected from the disruptions of REMD. From all of this they
concluded that SWS was not responsible for task improvement but that REM sleep improved
performance (and improved memory) on a novel task.
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Reasons Why Somebody Might Argue REM Sleep Does Not Improve Memory
Although the type of task appears to be the defining factor in whether or not REM
sleep will improve memory, this has not been proven. From the classifications of the tasks our
studies use, all tasks that had a cognitive aspect showed an improvement in memory, and those
that were purely motor, showed no improvement. However, these studies are not perfect, and
there may have been factors such as circadian rhythm and the use of REM deprivation (REMD)
that unexpectedly affected the results, wrongly leading us to our conclusion.
Researchers are starting to consider the importance of circadian rhythm in relation to
learning and memory, and now believe that it may affect how a subject performs on a task. Have
you ever noticed that maybe you study better in the morning than at night? This is due to a
circadian rhythm, the body’s natural sleep and alertness cycle. Many researchers have stressed its
importance, and claimed that without this control, a study’s results may be affected. This is
because if a subject is trained in the morning when they are most alert and tested the next night
(after a REM sleep cycle), the subject could show no improvement even if their memory
improved, merely because they were less alert during the testing. The same goes if training and
testing times are switched, which could show a false improvement. Within the eight studies we
looked at, five did not control for circadian rhythm (Donchin et al., 2002; Maquet et al., 2001;
Plihal and Born, 1997; and Smith and Macneill, Experiment 2, 1994), and four did include this as
a control (Karni et al., 1994; Cai and Rickard, 2009; Hupbach et al., 2009; and Smith and
Macneill, Experiment 1, 1994). Because the majority of the studies did not control for this
variable, it is possible that circadian influences could have affected the results enough to change
the outcome of the study, in which case not all studies that had a cognitive aspect would have
shown an improvement after REM sleep.
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However, this is not likely. When we looked at all the studies, no matter whether or not
circadian rhythm was controlled for, all studies that fell into the category of “yes, REM sleep
improves memory” had tasks with a cognitive aspect, and all those that fell into the category of
‘no, REM sleep does not improve memory’ had tasks that were purely motor (Figure 4). This
shows that the influence of circadian rhythm was not significant enough to trump the major
effect that the type of task had on the outcome of the results.
Researchers have also questioned the use of REMD (REM deprivation) in studies
because it has the potential to show that REM sleep improves memory when it actually does not
(Vertes and Eastman, 2000). Depending on the way a subject is woken up during REM sleep
(REMD), these methods can actually be physically tolling to the point where it affects a subject’s
performance on a task. For example, in a study that showed REM sleep improved memory, and
that REMD blocked this improvement, it is possible that no improvements in memory were seen
in the REMD group because of the way the subject was deprived of REM. If the way of
depriving a subject of REM sleep is highly stressful (i.e. a rodent subject is placed on a small
floating device- when it enters REM sleep it loses muscle tone, falls in, and is abruptly woken
up), the stress can cause the subject not to perform as well when tested the next day because of
physical exhaustion. Because of this, it would appear that without REM sleep, memory would
not improve. However, if this improvement was blocked because of the methods of deprivation,
then it is possible that both the REM and REMD groups would have shown an improvement to
memory. This would mean that REM sleep is not responsible, and that it would actually be some
other stage of sleep that improves memory.
Although five out of our eight studies (Donchin et al., 2002; Smith and Macneill, 1994;
Gais et al., 2000; Karni et al., 1994; Plihal and Born, 1997) used REMD, this argument usually
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refers to methods used on animals, and not on humans. Humans are typically woken up by an
electronic bell (like an alarm) or gently by a researcher, neither of which is something that would
cause enough physical or mental stress to affect performance on a task. Because all of the studies
we analyzed used human subjects, and the methods of REMD were not highly stressful, it is
possible but not probable that the use of REMD affected the results enough to alter the
conclusion.
Conclusion
As of now, research in the area of learning and memory is limited, and more studies
need to be done in order to gather additional information as new advancements are made in this
field. One such aspect that needs to still be explored is the type of task in relation to the
improvement of memory. Current studies show conflicting conclusions on whether or not REM
sleep will improve memory; however, these studies have not taken into account this factor of the
types of tasks being used. When we sort the studies by the type of task, patterns show that only
studies that are purely motor do not improve memory, and those that have any sort of cognitive
aspect, do improve memory. This conclusion is also supported by the fact that during a mixed
motor and cognitive task, the brain areas active during the performance of the task are also
reactivated during REM sleep. So next time you are debating whether to pull an all-nighter or to
get a few hours of sleep, consider the fact that getting even a little bit of REM sleep could
improve your memory, and give you an A on that exam.
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FIGURES (not in text)
Figure 1. Studies That Show Whether or Not REM Sleep Improves Memory, and the Type
of Task Used in Each
Study
Maquet et al.
Does
REM
Sleep
Improve
Memory?
Yes
Hupbach et al.
Yes
Plihal & Born
Yes
Karni et al.
Yes
Gais et al.
Yes/No
Cai & Rickard No
Donchin et al.
No
Smith &
Macneill
(Experiment
1&2)
No
Task
Visual-Motor
(StimulusResponse)
Recognition of
an Unfamiliar
vs. Familiar
Artificial
Language
Mirror Tracing
Task
Visual-Motor
(Texture
Discrimination)
Visual-Motor
(Texture
Discrimination)
Finger-Tapping
Pattern
Robotic Arm
Moved Through
Varying ForceFields
Pursuit Rotor
Cognitive
Component
Motor
Component
-
-
-
Figure 1. All studies that found that REM sleep doesn’t improve memory used tasks that were
purely motor. Conversely, all studies that found that REM sleep improved or had mixed findings
used tasks that were both purely cognitive or a mix of cognitive and motor.
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Figure 4. Studies that support or refute our conclusion and whether or not
they controlled for circadian rhythms
REM Sleep DOES Improve Memory
REM Sleep Does NOT Improve Memory
Controlled for Circadian Rhythm (2)
Hupbach et al. (Experiment 1 & 2)
Purely Cognitive
Karni et al.
Cognitive & Motor
Controlled for Circadian Rhythm (2)
Cai & Rickard
Purely Motor
Smith & Macneill (Experiment 1)
Purely Motor
No Control for Circadian Rhythm (2)
Maquet et al.
Cognitive & Motor
Plihal & Born
Cognitive & Motor
No Control for Circadian Rhythm (2)
Donchin et al.
Purely Motor
Smith & Macneill (Experiment 2)
Purely Motor
Figure 4. Regardless of whether or not circadian rhythm was controlled for, all studies that show
that REM sleep improves memory have tasks that are either cognitive, or a mix of motor and
cognitive, and all those that show that REM sleep does not improve memory are all purely
motor. Because of this, it is clear that circadian rhythm did not alter the results of the studies
enough to make them stray from the classification of type of task. We removed the study with
mixed findings (Gais et al.) in this figure because it makes the separation of studies more clear.
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