Article

The effects of napping on cognitive functioning

Abstract and Figures

Naps (brief sleeps) are a global and highly prevalent phenomenon, thus warranting consideration for their effects on cognitive functioning. Naps can reduce sleepiness and improve cognitive performance. The benefits of brief (5-15 min) naps are almost immediate after the nap and last a limited period (1-3h). Longer naps (> 30 min) can produce impairment from sleep inertia for a short period after waking but then produce improved cognitive performance for a longer period (up to many hours). Other factors that affect the benefits from the nap are the circadian timing of the nap with early afternoon being the most favourable time. Longer periods of prior wakefulness favour longer naps over brief naps. Those who regularly nap seem to show greater benefits than those who rarely nap. These conclusions, however, need to be accepted cautiously until more comprehensive research programmes are conducted in which all these parameters are varied. Research is also needed to test the benefits of brief naps taken more naturalistically at the time when sleepiness becomes intrusive. The significant benefits of a brief nap, containing virtually no slow wave EEG activity, are not predicted by the present theory of homeostatic sleep drive (Process S). A new biological process (Process O) suggests that sleep onset followed by only 7-10 min of sleep can result in a substantial increase of alertness because it allows the rapid dissipation of inhibition in the 'wake-active' cells associated with the 'sleep-switch' mechanism rather than the dissipation of Process S.
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From Nicole Lovato and Leon Lack, The effects of napping on cognitive functioning. In: Gerard A.
Kerkhof and Hans P.A. van Dongen, editors: Human Sleep and Cognition, Vol 185, Oxford: Elsevier
Science; 2010, p. 155-166.
ISBN:978-0-444-53702-7
© Copyright 2010 Elsevier B.V.
Elsevier Science.
Provided for non-commercial research and educational use only.
Not for reproduction, distribution or commercial use.
CHAPTER 9
The effects of napping on cognitive functioning
Nicole Lovato and Leon Lack
*
School of Psychology, Flinders University, Adelaide, SA, Australia
Abstract: Naps (brief sleeps) are a global and highly prevalent phenomenon, thus warranting consider-
ation for their effects on cognitive functioning. Naps can reduce sleepiness and improve cognitive perfor-
mance. The benefits of brief (515 min) naps are almost immediate after the nap and last a limited period
(13 h). Longer naps (>30 min) can produce impairment from sleep inertia for a short period after waking
but then produce improved cognitive performance for a longer period (up to many hours). Other factors
that affect the benefits from the nap are the circadian timing of the nap with early afternoon being the most
favourable time. Longer periods of prior wakefulness favour longer naps over brief naps. Those who
regularly nap seem to show greater benefits than those who rarely nap. These conclusions, however, need
to be accepted cautiously until more comprehensive research programmes are conducted in which all these
parameters are varied. Research is also needed to test the benefits of brief naps taken more naturalistically
at the time when sleepiness becomes intrusive. The significant benefits of a brief nap, containing virtually no
slow wave EEG activity, are not predicted by the present theory of homeostatic sleep drive (Process S). A
new biological process (Process O) suggests that sleep onset followed by only 710 min of sleep can result in
a substantial increase of alertness because it allows the rapid dissipation of inhibition in the wake-active
cells associated with the sleep-switchmechanism rather than the dissipation of Process S.
Keywords: Naps; cognitive performance benefits; nap length; sleep inertia; sleep homeostasis; Process O
Overview
A nap is commonly referred to as a short sleep,
more specifically a sleep which is distinct from and
substantially shorter than an individuals normal
sleep episode (Dinges, 1989). Dinges et al. (1987)
define a nap in more quantitative terms as any
sleep period with a duration of less than 50% of
the average major sleep period of an individual
(p. 313). The briefest naps may consist of only a few
E-mail: Leon.lack@flinders.edu.au
*
Corresponding author.
Tel.: (+) 618 8201 2391; Fax: (+) 618 8201 3877.
G. A. Kerkhof and H. P. A. Van Dongen (Eds.)
Progress in Brain Research, Vol. 185
ISSN: 0079-6123
Copyright Ó2010 Elsevier B.V. All rights reserved.
DOI:10.1016/B978-0-444-53702-7.00009-9 155
minutes of sleep and the longest up to several
hours of sleep. Most commonly nap lengths range
from 30 to 90 min (Dinges, 1989). Napping is con-
sidered a global phenomenon that occurs during
infancy and persists into adulthood for a large pro-
portion of the worlds population (Stampi, 1992).
Dinges (1989) conducted a comprehensive review
of studies which investigated the prevalence of
napping among the adult population. The preva-
lence of regular napping (at least once per week)
was reported to vary greatly across countries from
33 to 84%, with the greatest prevalence among
countries located close to the equator (Dinges,
1989). More recently, Pilcher et al. (2001) reported
similar rates of napping, indicating that approxi-
mately 74% of young and middle-aged adults liv-
ing in the United States reported napping at least
once per week.
A multitude of research has investigated the
effects of napping and has consistently demon-
strated that naps can counteract the effects of
sleepiness by enhancing subjective and objective
alertness, improving cognition, vigilance and psy-
chomotor ability. This chapter will review the cur-
rent literature investigating the effects of naps,
outline several factors that can affect the recuper-
ative value of a nap, and will discuss potential
applications for napping within industry and health
care. The chapter will also explain how the recu-
perative benefits of brief naps cannot be explained
by the present conceptualization of homeostatic
sleep drive and thus requires a new sleep process
(Process O) in addition to the three-process model
(A
kerstedt and Folkard, 1997).
For many individuals, napping offers a practical
solution to reduce sleepiness. Naps taken for this
reason are referred to as replacement or compen-
satory naps. This type of napping strategy is com-
mon among shift workers, individuals suffering
from sleep disorders associated with excessive day-
time sleepiness and those who have a restricted
main sleep episode (Dinges, 1992; Dinges et al.,
1981). However, researchers have acknowledged
that this is not the only reason individuals may nap.
In some circumstances, individuals may choose to
nap in anticipation of sleep loss, or to avoid feelings
of sleepiness later on. This type of napping is
referred to as prophylactic, and is common among
shift workers particularly before beginning
extended shifts (Stampi, 1992). Although the
majority of experimental research has focused on
these types of napping, it has also been reported
that some people nap in the absence of sleep loss,
due to feelings of boredom or for enjoyment.
A
kerstedt et al. (1989) have termed this type of
napping as appetitive or recreational.
Benefits of naps
The high prevalence rates of napping around the
globe alone are suggestive that napping is benefi-
cial (Brooks and Lack, 2006; Dinges, 1989). The
benefits of naps have been supported by a number
of experimental research paradigms (Betrus, 1986;
Bonnet, 1991; Brooks and Lack, 2006; Hayashi and
Hori, 1997; Hayashi et al., 2003; Lovato et al., 2009;
Milner et al., 2006; Takahashi and Arito, 2000;
Tietzel and Lack, 2001, 2003; Tucker and
Fishbein, 2008). Naps have not only been shown
to reduce subjective and objective sleepiness but
can also improve cognitive functioning and psycho-
motor performance and enhance short-term mem-
ory and mood (Brooks and Lack, 2006; Hayashi
and Hori, 1997; Takahashi and Arito, 2000;
Tamaki et al., 2000; Tietzel and Lack, 2003;
Tucker and Fishbein, 2008).
Research has also investigated whether the
effects of napping are comparable to other coun-
termeasures commonly used to reduce sleepiness
and performance impairments, such as caffeine
and stimulant medications. Bonnet et al. (1995)
showed that a prophylactic nap produced improve-
ments to performance, mood and alertness which
were longer lasting and less variable when com-
pared to improvements following caffeine.
Mednick et al. (2008) reported that naps signifi-
cantly improved declarative verbal memory rela-
tive to both caffeine and a placebo. In a similar
study, Reyner and Horne (1997) assessed the
156
efficacy of a 15-min nap, caffeine intake or a com-
bination of both on performance using a driver-
simulator task. Caffeine taken in conjunction with
the nap resulted in a threefold reduction in acci-
dents when compared to caffeine alone.
Limited research has investigated the benefits of
naps relative to currently available stimulant med-
ications such as modafinil. Batejat and Lagarde
(1999) assessed the effects of naps, modafinil or a
combination of both, on cognitive functioning dur-
ing sleep deprivation. The naps were found to
significantly improve psychomotor performance;
however, these benefits were strengthened when
naps were taken in conjunction with modafinil.
The restorative effects of naps have been well
established across a variety of alertness and per-
formance domains, with improvements evident
across a wide range of objective and subjective
sleepiness measures and cognitive performance
measures. Naps are found to have alerting benefits
that are comparable, and often superior, to other
countermeasures against sleepiness and perfor-
mance decrements (Batejat and Lagarde, 1999;
Bonnet et al., 1995; Mednick et al., 2008; Reyner
and Horne, 1997). However, there are a number of
factors to consider when aiming to optimize the
beneficial effects of a nap, including the duration
of the nap and circadian timing of the nap.
Duration of the nap and sleep inertia
Research has demonstrated that the length of a
nap can determine its effect on alertness and cog-
nition (Bonnet, 1991; Kubo et al., 2007; Tietzel and
Lack, 2001). Naps of all durations (from 5 min to
2 h) have been shown to have some benefits to
cognition (Brooks and Lack, 2005). However, it
is the way in which these benefits emerge over
the period following the nap that produces the
most evident differences between different length
naps. The benefits of a brief nap (e.g. 10 min of
sleep) emerge almost immediately following the
nap and can last up to 3 h (Brooks and Lack,
2006). However, immediately following long naps
(e.g. 2 h) performance can actually decline for a
period with eventual improvements that can last
up to 24 h (Achermann et al., 1995; Jewett et al.,
1999; Lumley et al., 1986). Figure 1 illustrates the
tentative conclusions we can draw about the gen-
eral time course of negative and positive effects on
cognition for brief (e.g. 10 min), short (e.g. 30 min)
[(Fig._1)TD$FIG]
Fig. 1. Relative changes in detrimental and beneficial effects of brief, short and long naps following awakening from the nap.
157
and long (e.g. 2 h) naps. Still needed is a systematic
parametric programme of research in which length
of nap, time of nap and amount of prior sleep
restriction are all varied while using a comprehen-
sive set of outcome measures of alertness and cog-
nitive performance administered over at least a 3-h
period following the nap.
The temporary deterioration of performance
immediately following long naps has been attrib-
uted to sleep inertia. Naitoh and Angus (1989)
describe sleep inertia as inferior task performance
and/or disorientation occurring immediately after
awakening(p. 226). Sleep inertia reflects a transi-
tion from a sleep state to a wake state and is char-
acterized by electroencephalography patterns,
which resemble Stage 1 sleep patterns (Naitoh
and Angus, 1989) rather than wake (Naitoh
et al., 1993).
The magnitude of sleep inertia is dependent on
several factors the most important of which is the
quantity of slow-wave sleep (SWS) contained
within the napping episode (A
kerstedt and
Folkard, 1991). Although the quantity of SWS is
positively correlated with the recuperative value of
a nap, particularly when considering improve-
ments to short-term memory performance
(Schmidt et al., 2006; Tucker et al., 2006), it is also
positively correlated with the intensity and dura-
tion of sleep inertia (A
kerstedt and Folkard, 1991).
Since SWS normally develops gradually over time
asleep, longer naps, at least up to the point of
maximum slow-wave activity (SWA) in a sleep
cycle, are expected to result in longer and more
intense periods of sleep inertia.
The magnitude of sleep inertia is also influenced
by prior sleep debt, circadian time and sleep stage
at awakening (Tassi and Muzet, 2000). Sleep iner-
tia is the most persistent from sleep episodes taken
during the circadian nadir, under conditions of
high sleep debt and waking from SWS (Tassi and
Muzet, 2000). The substantial sleep inertia arising
from these longer naps can be ameliorated to some
extent by consuming caffeine on awakening
(Bonnet and Arand, 1994; Schweitzer et al., 2006;
Van Dongen et al., 2001).
Brief naps (less than 20 min) have been shown to
ameliorate sleepiness and improve performance
after both a restricted nocturnal sleep and a noc-
turnal sleep of normal duration (Hayashi et al.,
2005; Tamaki et al., 2000; Tietzel and Lack, 2002,
2003). A number of researchers have demon-
strated that naps as brief as 10 min in duration
can improve subjective and objective alertness,
increase feelings of vigour and decrease fatigue,
in addition to improving accuracy and speed on a
number of cognitive tasks (Brooks and Lack, 2006;
Horne and Reyner, 1996; Takahashi and Arito,
2000; Tietzel and Lack, 2002). One study has found
that a nap as brief as 7 min is beneficial for restor-
ing alertness (Takahashi et al., 1998). Unlike long
naps, the beneficial effects of brief naps are evident
almost immediately after waking (Tietzel and
Lack, 2002). Brief naps are associated with shorter
periods of sleep inertia, and in some instances, no
sleep inertia (Tietzel and Lack, 2002).
Although research suggests that both brief and
long naps are beneficial for improving alertness,
few studies have used the same protocol and out-
come measures to directly compare the benefits of
brief and long naps. This remains an important
research programme to be pursued. Nevertheless,
it is suggested that for sleep restricted individuals
and individuals who have experienced normal noc-
turnal sleep duration, brief naps and long naps
produce comparable benefits to alertness
(Brooks and Lack, 2006; Takahashi et al., 1998;
Taub et al., 1976; Tietzel and Lack, 2001). It is only
in the case of total sleep deprivation that naps of a
longer duration (12 h) have been demonstrated
to elicit greater alerting benefits than brief naps
(Helmus et al., 1997; Lumley et al., 1986).
Circadian placement of the nap
The recuperative value of a nap is also dependent
on when the nap is taken with respect to the 24-h
circadian rhythm (e.g. as reflected in core body
temperature). The three-process model of alert-
ness (A
kerstedt and Folkard, 1991) proposes that
158
the maximum period of circadian sleepiness occurs
in the early hours of the morning (03000600 h). A
secondary period of sleepiness occurs in the mid-
afternoon (13001600 h), referred to as the post-
lunch dip period (A
kerstedt and Folkard, 1991).
Experimental studies using both continuous wake-
fulness and sleep/wake ultradian routines across
the 24-h day, have also reported peaks in sleepi-
ness and napping at these times (Broughton, 1989;
Lack and Lushington, 1996; Lack et al., 2009;
Lavie, 1989). Since most individuals take their
main sleep nocturnally across the maximum period
of circadian sleepiness, the preferred time to nap is
usually reported to be during the post-lunch dip
period between 1300 and 1600 h (Broughton,
1989).
Research has indicated that naps taken during
the post-lunch dip period have a greater recuper-
ative value than when naps are taken in the early
morning, late morning or evening (Naitoh and
Angus, 1989; Taub et al., 1978). Researchers have
further established the optimum time to nap during
the 3-h post-lunch dip period. Hayashi et al.
(1999a, 1999b) compared a 20-min nap taken at
noon or 1400 h relative to a no-nap control condi-
tion. The 20-min nap scheduled at 1400 h produced
both greater and longer lasting benefits to mood,
fatigue, objective performance, self-rated perfor-
mance and objective alertness, when compared to
the 20-min nap scheduled at noon.
Naps taken during the circadian nadir (approx-
imately 0400 h) produce less recuperative value
when compared to naps taken during the day or
in the early hours of the morning. Sallinen et al.
(1998) found that 30- and 50-min naps taken by
shift workers at 0100 h improved objective alert-
ness; however, when the same naps were taken
closer to the circadian nadir at 0400 h, no alerting
benefits were observed. Purnell et al. (2002)
reported benefits in performance after a 20-min
nap when taken at either 0100 or 0300 h, while
Saito and Sasaki (1996) found that 1-h naps ending
at either 0400 or 0500 h had no alerting benefits for
subjective fatigue. It is still difficult at present to
come to confident conclusions about the effect of
circadian phase on napping effects from the sparse
evidence available from a few studies using differ-
ent measures and methodologies. This strengthens
the earlier point about the need for a comprehen-
sive research programme testing a variety of circa-
dian times with a variety of nap lengths.
Other factors: prior wake time and experience with
napping
Research has also suggested that other factors such
as prior wake time and experience with napping
can contribute to the duration and magnitude of
alerting benefits (Dinges, 1995; Dinges et al., 1987;
Rosa et al., 1983). Several researchers have dem-
onstrated that naps taken after long periods of
wakefulness (e.g. 18 h) are less effective and have
shorter-lasting benefits than naps taken after
shorter periods of wakefulness (Dinges, 1995;
Dinges et al., 1987). Additionally, research has
concluded that the longer an individual has been
awake, the longer a nap needs to be to improve
alertness (Dinges, 1995; Dinges et al., 1987).
A limited amount of research has been con-
ducted on the impact experience with napping
can have on the recuperative effects of a nap.
Taub and colleagues (Taub, 1979; Taub and
Berger, 1973; Taub et al., 1976, 1977, 1978) con-
ducted several studies investigating the alerting
benefits of naps for individuals who habitually
nap (one or more times per week for at least 2
years). Taub and Berger (1973) reported that an
afternoon nap improved the mood and perfor-
mance of habitual nappers. Evans et al. (1977)
extended Taub and Bergers (1973) work to com-
pare the benefits of a nap for habitual nappers and
non-nappers. In this study, participants who regu-
larly napped reported feeling more satisfied and
less sleepy and tired following an afternoon nap
when compared to participants who did not nap
on a regular basis. Recently, Milner et al. (2006)
reported that a short nap improved motor learning
performance for individuals who regularly napped,
but was detrimental for those who were not
159
habitual nappers. Contrary to these findings, other
studies have demonstrated no significant differ-
ences in performance for habitual and non-habit-
ual nappers following an afternoon nap (Daiss
et al., 1986; Keyes, 1989). Further research is
required to clarify the differential effects of naps
for habitual and non-habitual nappers (Milner and
Cote, 2008). Perhaps habitual nappers choose to
nap on a regular basis because they experience a
greater benefit from the nap. Habitual nappers
may be chronically sleep restricted and require
naps to achieve acceptable alertness levels during
the day. Differences between regular nappers and
non-nappers could thus be compared after several
nights of unlimited sleep opportunity in order to
eliminate any residual effects of sleep restriction.
Can experiments capture the naturalistic use of
napping?
There is considerable experimental support for the
ability of brief naps to increase alertness as evi-
denced in measures of subjective feelings, objec-
tive sleep latency and objective measures of cogni-
tive performance. All of these studies administered
nap opportunities at scheduled times in fixed
experimental protocols. They were not self-
selected times that, in a more naturalistic situation,
would usually determine the timing of a nap. In
practice, an individual is likely to take a nap when
sleepiness becomes so intense that it interferes
with ongoing activity and when opportunity or con-
ditions (physical and social) allow. Most of us in
our mildly sleep-restricted lives have experienced
occasional drowsiness and the struggle to remain
awake whether it is during an uninteresting lecture
or meeting, some quiet reading or study in the early
afternoon, or in front of the television in the even-
ing (Johns, 1991). A common anecdotal report is
that a brief nap at that time can remarkably
remove the drowsiness feeling and restore cogni-
tive functioning. The experimental evidence sup-
ports these reports. We predict that an experiment
that allowed a self-selected nap time at the point of
heightened drowsiness would show even more
impressive improvements in subjective alertness
as well as objective cognitive performance.
Theoretical implications of brief nap benefits
The research confirming the benefits of brief naps
not only has applied importance but it can also
contribute to theoretical biological models of sleep
propensity. The apparent rapid reversal of sleepi-
ness following a brief nap suggests the need for a
biological mechanism additional to the presently
accepted three-process model that includes sleep
homeostasis (Process S), circadian phase (Process
C) and sleep inertia (Process W) (A
kerstedt and
Folkard, 1997). The three-process model would
suggest that if the circadian factor was kept rela-
tively constant and any sleep inertia were allowed
to dissipate, any benefits of a brief sleep would be
entirely dependent on the decrease of homeostatic
sleep drive (Process S) following sleep onset. The
original simplified conceptualization of the dissipa-
tion of Process S was represented by an exponen-
tial decaying function in which the rate of decay
was maximal following sleep onset (Daan et al.,
1984). However, the model was then revised to
indicate that the decrease of homeostatic sleep
drive during sleep is entirely dependent of the
amount of SWA that varies across sleep with an
ultradian rhythm of an approximately 90-min
period length (Achermann and Borb
ely, 1990).
Thus, Process S would dissipate most rapidly when
SWA is at a maximum, but this would not occur
immediately at sleep onset. It would increase grad-
ually over 2070 min with the gradual increase in
SWA. The ultradian rhythm of SWA during sleep
and the predicted decrease of Process S is illus-
trated in Fig. 2.
This dissipation function of Process S during
sleep would suggest that the longer the sleep or
the nap, especially the more SWA included in the
sleep, the greater the benefit for alertness or
decrease of sleepiness. However, the data suggest
considerable benefits to alertness from very brief
160
(710 min of sleep) naps. Yet, in terms of satisfying
accumulated homeostatic sleep drive, such a brief
and light sleep with virtually no SWA should result
in virtually no decrease in Process S and thus pro-
vide almost no benefit. For example, Fig. 2 shows
very little decrease of Process S in the first 15 min
of sleep. However, in comparison with longer naps
(2060 min of sleep) containing much more SWA,
the benefits following brief naps are surprisingly
comparable. These benefits are maintained even
after allowing for the dissipation of the negative
effects of sleep inertia immediately following a
longer sleep. This suggests some other mechanism,
apart from homeostatic sleep drive, determines the
improvement of alertness and performance follow-
ing brief naps.
This additional process may incorporate what
Saper et al. (2001) have termed as a sleep-switch
mechanism. This is a bi-stable, flip-flopcircuit
that spends little time in transition and promotes
stability of either sleep or wake. Evidence suggests
the sleep-switch mechanism involves nuclei of
sleep-active neurons and opposing nuclei of
wake-active neurons with mutual inhibitory con-
nections. When the balance is tipped in favour of
sleep, as a result of accumulated homeostatic sleep
drive, high circadian sleep propensity or sleep-
conducive circumstances, the sleep-active nuclei
increase their activity and thus increase their inhi-
bition of the wake-active neurons. With the
decreased activation of the wake-active neurons
there would be less inhibitory feedback to the
[(Fig._2)TD$FIG]
Fig. 2. Revised dissipation of homeostatic sleep drive (Process S) as a function solely of slow-wave activity during the sleep period
illustrating very little decrease of Process S for brief (<15 min of sleep) naps.
161
sleep-active neurons and the switch to sleep would
occur quickly and then tend to be maintained by
strong inhibition of the wake-active neurons. The
process is analogous to the switches that occurs
when breathing (from inspiration to expiration
and the opposite change), these also being con-
trolled by groups of mutually inhibitory neurons.
An additional sleep process (Process O)
We suggest that alertness can be increased a con-
stant amount simply through the process of sleep
onset (or Process O) (Lack and Tietzel, 2000).
What exactly constitutes sleep onset in this sense
and how brief the period of sleep needs to be and
still satisfy this process has already been explored
to some extent. It appears to require more than the
onset of Stage 1 sleep since ultra-brief naps of 30
90 s of sleep produce no measurable benefit
(Tietzel and Lack, 2002). Hayashi et al. (2005)
have suggested that it is not the onset of Stage 2
but the presence of at least 3 min of Stage 2 sleep
following 45 min of Stage 1 sleep that provides the
benefits of a brief nap. More recently, Brooks and
Lack (2006), by comparing different nap lengths
(5, 10, 20 and 30 min sleep), obtained data that
suggested an elapsed amount of sleep (about
10 min) or the onset of some SWA are potential
candidates for the benefits of Process O.
This proposed mechanism may be intrinsic to
the sleep switch itself rather than an external
factor (elsewhere in the brain) playing upon it such
as Process S or C. As Saper et al. (2001) describe,
when the switch flopsto the sleep state, the sleep
nuclei become active and the wake-active nuclei
are inhibited and, as a result, become inactive.
The mechanism we suggest would incorporate a
fatigue or adaptation process that builds up slowly
over the period of activation with a time constant in
the order of hours. This would gradually decrease
the excitability of the active neural centre.
However, with a flip or flop of the sleep switch,
the previously active centre is turned off during
which the accumulated fatigue or satiation
(lowered excitability) dissipates relatively rapidly
with a time constant more in the order of minutes.
Thus, during a brief (e.g. 10 min) sleep, excitability
returns almost entirely to the now inactive wake
centre. If an awakening then occurs, the wake-
active nuclei have regained most of their maximal
excitability and provide a significant increase of
alertness or decrease of the prior sleepiness. This
would account for the relatively rapid improve-
ment in alertness following a brief nap and its ben-
efits lasting in the order of 23 h as fatigue slowly
builds again in the wake-active nuclei.
This return of excitability to the wake-active cen-
tre during a brief nap does not flip the switch back
to awake on its own, since it is still being inhibited
by the still active sleep centre. Therefore, if one
desirestolimitthelengthofanaptoabrief
1015 min it would be advisable, particularly for
inexperienced nappers, to use a timed alarm.
Interestingly, there are anecdotal reports from
experienced brief nappers that they are usually able
to awake spontaneously to ensure a brief nap only.
This is an interesting question that deserves some
research to explore its applied utility.
The existence of differential time constants
between reduction of excitability during activation
and return of excitability at the cessation of activity
is not a novel mechanism in physiology and behav-
iour. There are other analogues of this process
such as sensory adaptation, habituation and reac-
tive inhibition (Hull, 1951). These processes have
similarities with a relatively slow build up of inhi-
bition during activation and a relatively rapid dis-
sipation of this inhibition or return of excitability
following cessation of activity (Duncan, 1956). As
a further example, the time-constants are very dif-
ferent between activation and de-activation of
sodium and potassium voltage-gated channels dur-
ing the generation of an action potential in excit-
able tissues.
The anecdotal scenario described above, in
which strong drowsiness is alleviated following a
brief nap, could be explained in terms of Process O
which is intrinsic to the sleep-switchmechanism
of Saper et al. (2001). The strong drowsiness
162
feeling would be an indication that the input to the
sleep switch from situational and behavioural vari-
ables was moving the switch closer to the threshold
of sleep or tipping the position of the switch very
close to a flopinto sleep. Then allowing sleep to
occur for the few minutes to maximally satisfy
Process O would return excitability to the wake-
activenuclei and result in noticeably increased
alertness upon awakening.
We are not suggesting that this dissipation of
fatigueor recovery of excitability of the wake-
active nuclei is enough on its own to overcome
Process S, which has decreased very little during
this brief sleep. The maximum effect of this intrin-
sic mechanism, Process O, in comparison with
Process S needs to be investigated by considerably
more research. However, our guess is that it is
significantly weaker than the effect of accumulated
Process S during 16 h of wakefulness in a normal
day. We suggest that this Process O is similar in
operation to Process S but with a much shorter
time scale and smaller maximum intensity. Thus,
although it accumulates fatigue much more slowly
than it dissipates it, the time scale to maximum
fatigue would be in the order of 23 h and dissipa-
tion complete in 815 min. In contrast, Process S
can accumulate sleep pressure over days of total
sleep deprivation and require over 1012 h of sleep
to dissipate entirely.
Parenthetically, the most parsimonious assump-
tion of the operation of this process on the sleep
switch is that it operates symmetrically for brief
awakenings during the major sleep period as it
would for brief sleeps during the major wake
period. That is a brief (510 min) awakening from
the major sleep period should rapidly dissipate
fatigue from the sleep-active nuclei thus facilitating
the re-establishment of sleep when it recurs. Such a
re-establishment of sleep, in conjunction with
Process W, sleep inertia (still potent only after
510 min of wakefulness) and maximal sleepiness
from Process C towards the end of the normal
sleep period, should all help to maintain the conti-
nuity of the major sleep period (Dijk and Czeisler,
1994).
Relative impacts of brief and long naps on
subsequent nocturnal sleep and clinical
implications
The substantial SWS contained in longer naps has
been demonstrated to disturb the duration and
architecture of the subsequent nocturnal sleep
period (A
kerstedt et al., 1989; Dinges, 1989). For
this reason, behavioural treatments of insomnia,
such as stimulus control therapy and bedtime
restriction therapy, that rely upon the increase of
sleep drive in the early stages of treatment, recom-
mend avoiding daytime naps that would lower the
therapeutic benefits of this temporarily raised
sleep pressure. On the other hand, brief afternoon
naps have not been shown to affect the length or
quality of the subsequent night sleep (Purnell et al.,
2002). Therefore, brief naps during the day to tem-
porarily reduce daytime sleepiness that may accu-
mulate during the initial stages of insomnia treat-
ment may be permissible. If successful at relieving
the sleepiness, the use of brief naps may improve
the compliance with these sometimes onerous
therapies. In addition, the adoption of this brief
nap strategy may provide the insomniac with a tool
to counteract the tiredness following a poor night
of sleep. Therefore, this new napping skill could
reduce the negative daytime consequences of poor
sleep and thus help to ameliorate the insomnia.
Applications for napping
The benefits of napping have been well established
and can be utilized in many situations to minimize
sleepiness and regain alertness. Naps of brief dura-
tion are particularly ideal for use within the work-
place as they can be taken during the employees
break time (Anthony and Anthony, 2005; Signal
and Gander, 2002). The minimal sleep inertia pro-
duced by brief naps also allows for maximum pro-
ductivity to resume almost immediately after wak-
ing from the nap. Research has suggested that brief
naps can temporarily relieve the excessive levels of
daytime sleepiness experienced by narcolepsy
163
suffers (Mullington and Broughton, 1993; Roehrs
et al., 1986; Rogers and Aldrich, 1993; Schulz et al.,
1992). Also, sleep apnoea patients with high levels
of daytime sleepiness regularly take naps to allevi-
ate bouts of sleepiness.
The use of napping is also recommended for
trans-meridian travel to allow the biological clock
to adapt en route (Kerkhof, 2009). Kerkhof (2009)
has also recently reported the use of multiple 10-
min naps by a solo sailor during long legs of a
journey when opportunities for longer sleeps were
not possible. Therefore, brief naps (power naps)
have anecdotal and research support for their
effectiveness in relieving sleepiness as well as
becoming a prompt for revising our theoretical
models of sleep.
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... Nap is generally referred to as short sleep, which is distinct from and substantially shorter than an individual's normal sleep episode. 1 People take a nap for a variety of reasons, such as making up for insufficient sleep, preparing for anticipated sleep loss, or taking it for enjoyment. 1,2 The duration of naps can range from a few minutes to several hours, on average 1 h. 1,2 Nap not only relieves sleepiness and enhances alertness, but also affects cognitive function, especially in strengthening short-term memory. ...
... 1,2 The duration of naps can range from a few minutes to several hours, on average 1 h. 1,2 Nap not only relieves sleepiness and enhances alertness, but also affects cognitive function, especially in strengthening short-term memory. [1][2][3] Previous studies on the relationship between nap and cognition have shown controversial results. ...
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Purpose Current evidence of whether napping promotes or declines cognitive functions among older adults is contradictory. The aim of this study was to determine the association between nap duration and cognitive functions among Saudi older adults. Methods Old adults (> 60 years) were identified from the Covid-19 vaccine center at Imam Abdulrahman Bin Faisal University, Dammam, Saudi Arabia between May and August 2021. Face-to-face interviews were conducted by a geriatrician or family physicians. Data collected for each participant included sociodemographic, sleep patterns, health status and cognitive functions. St. Louis University mental status (SLUMS) was used to assess the cognitive functions. A multi-Linear regression model was used to determine the association between cognitive functions and nap duration. Results Two-hundred participants (58 females) aged 66 ± 5 years were recruited. Participants were categorized according to their nap duration into non-nappers (0 min), short nappers (> 0- ≤ 30 min), moderate nappers (> 30–≤ 90 min), and extended nappers (> 90 min). The mean duration of the nap was 49.1 ± 58.4 min. The mean SLUMS score was 24.1 ± 4.7 units. Using the multi-linear regression model, the mean total SLUMS score for extended nappers was, on average, significantly lower than non-nappers [−2.16 units; 95% CI (−3.66, −0.66), p = < 0.01] after controlling for the covariates (age, sex, education level, sleep hours, diabetes mellitus, hypertension, pain). Conclusions Extended napping was associated with deterioration in cognitive function among Saudi older adults.
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Aim: The effect of sleep duration on cognitive function has been reported. However, the studies about the combined effects of total sleep duration and midday napping on cognition in elders were limited and inconclusive. We aimed to investigate the associations between total sleep duration, midday napping and cognitive function among middle-aged and older Chinese adults. Methods: Based on the 3rd wave of the China Health and Retirement Longitudinal Study (CHARLS) in 2015, a total of 9218 participants aged ≥45 years with completed cognition measurements were included. Cognitive functions were assessed by a combined global cognition score of episodic memory and mental status. Information about sleep-related variables, demographic characteristics, and health status were collected by validated questionnaires. Multivariate linear regression models were performed to evaluate the associations between total sleep duration, midday napping, and cognitive function. Stratified analyses were used to explore the potential effect modifier. Results: Overall, the global cognition score was 10.38 ± 4.30 among the participants (mean age: 61.5 ± 8.7 years). For sleep duration, both short sleep and long sleep duration were significantly associated with the increased risk of cognitive impairment after controlling for demographics and other confounders. Compared with sleeping for 7h per day, the adjusted β-coefficient and 95% CI of the risk of cognitive impairment was -0.967 (95% CIs: -1.191, -0.742) for ≤5h, -0.257 (-0.498, -0.016) for 6h, -0.424 (-0.650, -0.198) for 8h and -0.664 (-0.876, -0.452) for ≥9h. The combined effect analysis indicated that subjects with extended or without naps had a significantly higher risk of cognitive impairment in the ≤5h sleep time group (ref: 7h) and in extended nappers or without naps group (ref: short nappers). Subjects with extended naps or without naps might increase the risk of cognitive impairment, especially those having ≤5h total sleep time. Stratified analysis showed that participants aged ≥60 years without social activity increased the risk of cognitive decline. Conclusion: An inverted U-shaped association was observed between total sleep duration and cognitive function in Chinese elders, especially in those aged ≥60 years or without social activity. Short midday naps could mitigate the deleterious effects of poor sleep quality and shorter sleep duration on cognitive function. The findings could help us identify the vulnerable population and decrease the burden of cognitive impairment.
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Naps are increasingly considered a means to boost cognitive performance. We quantified the cognitive effects of napping in 60 samples from 54 studies. 52 samples evaluated memory. We first evaluated effect sizes for all tests together, before separately assessing their effects on memory, vigilance, speed of processing and executive function. We next examined whether nap effects were moderated by study features of age, nap length, nap start time, habituality and prior sleep restriction. Naps showed significant benefits for the total aggregate of cognitive tests (Cohen's d = 0.379, CI95 = 0.296–0.462). Significant domain specific effects were present for declarative (Cohen's d = 0.376, CI95 = 0.269–0.482) and procedural memory (Cohen's d = 0.494, CI95 = 0.301–0.686), vigilance (Cohen's d = 0.610, CI95 = 0.291–0.929) and speed of processing (Cohen's d = 0.211, CI95 = 0.052–0.369). There were no significant moderation effects of any of the study features. Nap effects were of comparable magnitude across subgroups of each of the 5 moderators (Q values = 0.009 to 8.572, p values > 0.116). Afternoon naps have a small to medium benefit over multiple cognitive tests. These effects transcend age, nap duration and tentatively, habituality and prior nocturnal sleep.
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Background Daytime napping on match-day is a strategy used by athletes to alleviate sleep debt or to avoid boredom. However, the utilization of pre-match napping and its effect on self-rated performance has not been evaluated in professional Rugby athletes. Methods Over a 17-match season, 30 professional Rugby Union athletes (mean ± SD: 23 ± 3 y) completed a weekly questionnaire on their daytime napping practices on match day. Questions included whether they took a nap, the duration of nap, their mood state upon waking and, their perceived performance during the subsequent match. Additionally, three team coaches evaluated the match performance of each participant. Finally, each participant was asked a questionnaire focusing on their napping preferences and individual habits of match-day napping at the conclusion of the season. Results Pre-match naps were used by 86% of athletes, with an average nap duration of 32 ± 19 min. A significantly greater number of naps were taken during away matches compared to home matches (60% vs. 40%, p < 0.01). Of the athletes who napped, 86% chose to nap less than 4 h before kick-off. Furthermore, 87% of athletes who napped on match day reported believing naps helped their match performance. Additionally, the odds of an athlete rating their performance as “good” was increased 6.7 times if they napped and won the match. Conclusion This study highlights that match-day naps are commonly used amongst professional Rugby Union athletes. The results suggest that taking naps before away matches may support self-rated performance amongst Rugby Union athletes.
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The discrepancies in the effects of napping on sleep quality may be due to differences in methodologies, napping behaviours, and daytime activity levels across studies. We determined whether napping behaviours and daytime activity levels are associated with night‐time sleep fragmentation and sleep quality in young adults. A total of 62 healthy adults (mean [SD] age 23.5 [4.2] years) completed screening questionnaires for sleep habits, physical activity, medical and psychological history. Actigraphy was used to record sleep including naps. The fragmentation algorithm (KRA) was applied to the actigraphic data to measure night‐time sleep fragmentation. We classified participants’ nap frequency as “non‐nappers” (0 naps/8 days), “moderate nappers” (1–2 naps/8 days) or “frequent nappers” (≥3 naps/8 days) naps. Nap duration was defined as “short” (≤60 min) or “long” (>60 min). Naps’ proximity to the night sleep episode was defined as “early” (≥7 h) and “late” (<7 h) naps. Outcome variables were night‐time KRA and actigraphic sleep variables. Frequent nappers had a significantly higher KRA than moderate nappers (p < 0.01) and non‐nappers (p < 0.02). Late naps were associated with poorer measures of night sleep quality versus early naps (all p ≤ 0.02). Nap duration and daytime activity were not associated with significant differences in the outcome variables (all p > 0.05). KRA correlated with sleep duration, sleep efficiency, and awakenings (r = −0.32, −0.32, and 0.53, respectively; all p < 0.05). Frequent napping and late naps may be associated with increased sleep fragmentation and poorer sleep quality, reflected in longer sleep onsets and increased awakenings. These findings have implications for public health sleep hygiene recommendations.
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Background: Identification of cognition status and its associated factors permit targeted interventions. This study aimed to: (i) investigate cognitive function of Chinese older adults using a large, nationally representative cohort; and (ii) explore its associated factors from aspects of socio-demographic, health behaviour, physical and mental health. Methods: Data on 2665 adults aged 65 and older from the China Health and Retirement Longitudinal Study wave 4 in 2018 were analyzed. Information on self-reported cognition status, socio-demographic characteristics, health behaviour, physical and mental health status were obtained. Hierarchical regression analyses were conducted to explore associated factors. Results: The cognition score was 24.8, with 41.1% of Chinese older adults identified as cognitively impaired. Better cognition was associated with being married, more education, living in a city/town or urban-rural integration zone, moderate night-time sleep (5-9 h) and post-lunch napping (less than 90 min), moderate/light physical activity for 30 min to 2 h every day, socially active and good health status; while worse cognition was associated with older age, intensive physical activity every day and more than 4 h a day, greater dependency in activities of daily living and depression. Conclusions: Cognitive impairment is a common health problem in Chinese older adults. Its associated factors are multifaceted, including socio-demographic characteristics, health behaviour and physical and mental health status. Developing interventions focused on these factors may be an important part of optimising cognition in these populations.
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In one of the first studies that examined the rest-activity behavior in a variety of animal species, Szymanski (1920) reported that several mammalian species exhibit numerous cycles (up to 10–12) of activity per day. Szymanski was the first to apply the term polyphasic to this fundamental and ubiquitous behavioral pattern, typical of most mammals, in which bouts of activity and rest alternate several times per day. Recent studies estimate that the majority (over 86%) of mammalian genera show typical polyphasic rest-activity patterns (Campbell and Tobler, 1984; see also Ball, Chapter 3, this volume).
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The aim of the present study was to examine the effects of short naps (less than 20 min) at noon for five consecutive days. Seven young adults (21-24 yrs) who had normal sleep-wake habits without habitual daytime napping participated in both the Nap and the No-nap conditions. During the Nap week between Monday and Friday, the subjects went to bed at 12:40 and were awakened at 13:00. During the No-nap week, they read a newspaper, sitting on a semi-reclining chair during that time. Subjective sleepiness and fatigue were evaluated immediately before and after napping and twice in the mid-afternoon (14:40 and 16:30). A visual detection task was also performed in the mid-afternoon. The subjects took a nap for approximately 12 min every five days. Sleep inertia occurred even after such a short nap. However, it was reduced as a function of days and became similar to the No-nap week on the fourth day. In the mid-afternoon, sleepiness was suppressed by not only taking a nap, but also taking it continuously for three days or more. These findings suggest that even a short nap of less than 20 min would cause sleep inertia, however, it would have positive effects upon mid-afternoon sleepiness. Furthermore, the effects of a short nap are enhanced by taking it for more than three consecutive days.