SHORT NOTE
http://dx.doi.org/10.5665/sleep.2322
Sleep to Implement an Intention
Susanne Diekelmann, PhD1,3; Ines Wilhelm, PhD1; Ullrich Wagner, PhD2; Jan Born, PhD1,3
1
Department of Neuroendocrinology, University of Lübeck, Lübeck, Germany; 2Division of Mind and Brain Research, Department of Psychiatry and
Psychotherapy, Charité University Medicine Berlin, Berlin, Germany; 3Department of Medical Psychology and Behavioral Neurobiology, University of
Tübingen and Center for Integrative Neuroscience, University of Tübingen, Tübingen, Germany
INTRODUCTION
Planning for the future is a central feature of human cognition.
The ability to form plans for future behavior and to implement
the planned behavior at a specific point in the future represents
an essential prerequisite for meaningful goal-directed behavior.1
Successful implementation of an intention requires a prospective
memory for the intention that allows executing the planned action
at the appropriate time.2 Sleep is well known to benefit the consolidation of memories.3 Subjects who are allowed to sleep after
learning show better memory retention than subjects who spend
an equivalent amount of time awake.4 Sleep thereby actively facilitates the consolidation and reorganization of memories for longterm storage rather than merely passively protecting memories
against decay and interference.5 However, the beneficial effect of
sleep on memory has been shown mainly for memories of past
events, whereas the possible role of sleep for memories of plans
and intentions for the future remained widely neglected.6 Here, we
asked whether sleep supports the implementation of a plan after a
delay of two days in a relatively naturalistic task and whether this
effect depends on slow wave sleep (SWS) or REM sleep.
adults participated in Experiment 1 and Experiment 2, respectively. All subjects reported regular sleep-wake cycles (≥ 6 h
sleep per night); had no history of any neurological, psychiatric,
or endocrine disorder; and did not take any medication at the
time of the experiments. Prior to the experimental night, subjects in the sleep groups spent one adaptation night in the sleep
laboratory. All subjects gave written informed consent and were
paid for participation.
Experimental Task
Plans for future behavior were experimentally induced by
means of a task introduced as a vigilance task (Figure 1A). During the initial “plan induction session,” subjects were required
to rapidly respond to a dot appearing on the left or right side of a
computer screen by pressing the corresponding button. The task
included 40 trials with the dot appearing every 2-10 sec (task
duration approximately 5 min). Importantly, the dot was in a
specific color (e.g., red) throughout the session. Subjects were
then instructed that at the retest session 2 days later they would
be tested again on the task, but on a slightly different version
with the dot in another color (e.g., green). The experimenter
emphasized that the participant should pay attention that the
correct version, with the dot in the new color, would indeed be
presented at retesting, because sometimes, due to a software
problem, the computer would display the wrong version. If
such mistake occurred, the participant should immediately inform the experimenter because otherwise the whole experiment
would have been performed in vain. To reduce possible effects
of experimenter biases to a minimum but at the same time keep
the instruction as naturalistic as possible, the experimenter literally read out a standardized instruction to the subjects. At retesting, without being reminded of the different versions and the
instructed plan, all subjects were presented with the allegedly
wrong version, i.e., with the dot in the same color as during the
plan induction session, and it was recorded whether subjects
METHODS
Participants
A total of 35 (9 females, mean age [± SD] 23.83 ± 3.74 years)
and 21 (6 females, mean age 23.90 ± 4.41 years) healthy young
Submitted for publication February, 2012
Submitted in final revised form June, 2012
Accepted for publication July, 2012
Address correspondence to: Susanne Diekelmann, PhD, Department
of Medical Psychology and Behavioral Neurobiology, University Tübingen, Tübingen, Gergmany; Tel: +49-7071-29-88917; E-mail: susanne.
diekelmann@uni-tuebingen.de
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Study Objectives: Sleep supports the consolidation of new memories. However, this effect has mainly been shown for memories of past events.
Here we investigated the role of sleep for the implementation of intentions for the future.
Design: Subjects were instructed on a plan that had to be executed after a delay of 2 days. After plan instruction, subjects were either allowed to
sleep or stayed awake for one night (Exp. 1) or had a 3-h sleep period either during the early night (SWS-rich sleep) or late night (REM-rich sleep;
Exp. 2). In both experiments, retesting took place 2 days later after one recovery night.
Setting: Sleep laboratory.
Patients or Participants: A total of 56 healthy young adults participated in the study.
Interventions: N/A.
Measurements and Results: All of the subjects who were allowed to sleep after plan instruction executed the intention 2 days later, whereas only
61% of wake subjects did so (P = 0.004; Exp. 1). Also after early SWS-rich sleep all of the subjects remembered to execute the intention, but only
55% did so after late REM-rich sleep (P = 0.015; Exp. 2).
Conclusions: Sleep, especially SWS, plays an important role for the successful implementation of delayed intentions.
Keywords: Intentional memory, plans, consolidation, sleep, SWS, REM sleep
Citation: Diekelmann S; Wilhelm I; Wagner U; Born J. Sleep to implement an intention. SLEEP 2013;36(1):149-153.
realized the “mistake.” At retesting, a longer version of the vigilance task was used, including 80 trials (task duration approximately 10 min), to allow for more possibilities to detect the
mistake. If subjects recognized the mistake, the experimenter
immediately started the “correct” version of the vigilance task
(including 40 trials again).
somnographic recordings. In the early sleep condition, initial
performance on the task and plan instruction took place between 22:30 and 22:45, and subjects went to bed at 23:00 to
allow a 3-h period of SWS-rich sleep. Subjects were awakened
at ~02:00 and stayed awake in the laboratory until 07:00. After
sleeping at home during the second night, they were retested
the following morning at ~10:00. In the late sleep condition,
subjects first slept for about 3 h between 23:00 and 02:00. To
prevent effects of sleep inertia, subjects were always woken up
from NREM sleep stages 1 or 2, and the initial session including performance on the task and plan induction started only 30
min after awakening. After this session, subjects went to bed
again (~03:30) to spend a 3-h period of REM-rich retention
sleep. After awakening in the morning, they left the laboratory
and returned for the retest at ~14:00 the next day. The retest
was shifted to 14:00 to match between conditions the length of
retention intervals and the amount of wakefulness between plan
instruction and retesting.
Procedures
In Experiment 1, participants were instructed on the task in
the evening before a night of sleep (n = 17) or wakefulness
(n = 18; Figure 1B, upper panel). Subjects in both conditions reported to the laboratory at 21:00, filled in questionnaires, and in
the sleep condition electrodes were attached for standard polysomnographic recordings. Initial performance on the vigilance
task and instruction on the plan took place between 22:30 and
22:45 in both conditions. In the sleep condition, subjects were
allowed to sleep between 23:00 and 07:00. Subjects in the wake
condition stayed awake throughout the night under supervision
of an experimenter, spending the time with standardized activities (reading, watching TV, or playing simple games). Subjects
in both conditions left the laboratory in the next morning. After
spending the day awake and another night of sleep at home,
they returned to the laboratory for the retest session at ~10:00.
This interval allowed subjects in the waking condition to recover from their initial sleep loss.
In Experiment 2, subjects participated either in the early
SWS-rich sleep (n = 10) or late REM-rich sleep condition
(n = 11; Figure 1B, lower panel). As in Experiment 1, subjects
in both conditions reported to the laboratory at 21:00, filled in
questionnaires, and were attached to the electrodes for polySLEEP, Vol. 36, No. 1, 2013
Control Variables
To control for general alertness and sleepiness, before the
initial session and after the retest session subjects rated their
subjective sleepiness on the Stanford Sleepiness Scale ranging from 1 (“feeling active, vital, alert, or wide awake”) to 7
(“no longer fighting sleep, sleep onset soon; having dream-like
thoughts”). Also, reaction times and error rates in the vigilance
task were analyzed. To this end, performance on the vigilance
task in the initial session as well as performance on the “correct” version in the retest session was analyzed, i.e., the task
that was started after subjects recognized the wrong version.
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Figure 1—Illustration of the experimental setup and results. (A) Experimental task. In the initial plan induction session, subjects performed on the vigilance
task first, before the experimental plan was induced. At retesting after 2 days, it was recorded whether or not subjects executed the plan (i.e., to inform the
experimenter about the wrong version). (B) Experimental design of Exp. 1 (sleep vs. wakefulness, upper panel) and Exp. 2 (SWS-rich early nocturnal sleep
vs. REM-rich late nocturnal sleep, lower panel). PI (Plan induction), R (Retest). (C-D) Percentage of subjects executing the plan in Exp. 1 and Exp. 2. (E)
Time spent in SWS and REM sleep in Exp. 2. Means ± SEM are shown. *P < 0.05, **P < 0.01, ***P < 0.001.
Experiment 2—SWS-rich vs. REM-rich Sleep
To answer the question whether the beneficial effect of sleep
on the implementation of intentions depends on SWS or REM
sleep, in a second experiment subjects performed the same task
as in Experiment 1, receiving exactly the same instructions, but
slept thereafter for 3 h either during the early night (dominated
by SWS) or during the late night (dominated by REM sleep).
After SWS-rich early sleep, all subjects (100%) remembered
the experimental plan to inform the experimenter about the
allegedly wrong task version, whereas only half the subjects
(55%) did so after late REM-rich sleep (χ2 = 5.97, P = 0.015,
Figure 1D). As in Experiment 1, most subjects recognized the
mistake in the first (n = 6), second (n = 6), third (n = 1), or
fourth trial (n = 2). One subject of the REM-rich group recognized the wrong task version only after 57 trials. Again, there
was no difference in the time point of recognizing the mistake
between groups (P > 0.30).
Polysomnographic recordings confirmed that the amount
of SWS during the experimental night was 5-fold higher during SWS-rich early than during REM-rich late retention sleep,
whereas the amount of REM sleep was about twice as high during late sleep as early retention sleep (P < 0.001, Figure 1E).
Time spent in other sleep stages did not differ between the sleep
periods (all P > 0.40; S1: 4.0 ± 0.9 vs. 5.0 ± 0.8 min, S2: 98.2
± 11.2 vs. 108.2 ± 8.2 min, for the SWS-rich and REM-rich
group, respectively). However, subjects in the late sleep condition displayed an overall shorter total sleep time than subjects
in the early sleep condition (182.1 ± 8.4 vs. 213.6 ± 6.4 min in
the REM-rich and SWS-rich group, respectively, P < 0.01). To
exclude the possibility that the improved ability to implement
the intention after the early period of sleep simply resulted from
a longer total sleep time, we omitted the 3 subjects who displayed the longest sleep times in the SWS-rich group as well
as the 3 subjects with the shortest sleep times in the REM-rich
group from analysis, resulting in comparable total sleep time in
both groups (194.9 ± 5.0 vs. 203.7 ± 1.9 min in the REM-rich
and SWS-rich group, respectively, P > 0.10). In this subsample, again all of the subjects with high amounts of SWS during
the retention interval remembered to execute the plan (100%),
whereas only 50% of subjects with predominant REM sleep remembered to do so (χ2 = 4.77, P = 0.029). As in Experiment 1,
both the SWS-rich and the REM-rich groups spent the second
night at home and sleep time and sleep quality were assessed
by self-report. Sleep time and sleep quality did not significantly
Statistical Analysis
The number of subjects who remembered to execute the plan
and informed the experimenter about the wrong task version
was analyzed using χ2-tests. Control variables were analyzed
using analyses of variance (ANOVA) and post hoc t-tests. Level
of significance was set to P = 0.05. Greenhouse-Geisser correction for degrees of freedom was applied where appropriate.
RESULTS
Experiment 1—Sleep vs. Wakefulness
All subjects (100%) who slept after initially forming the plan
remembered to inform the experimenter about the wrong task
version when performing the vigilance task with the different
color at delayed retesting, whereas only 61% of the wake subjects realized the mistake (χ2 = 8.26, P = 0.004, Figure 1C). Of
those subjects who recognized the wrong task version, most did
so in the first (n = 20), second (n = 5), or fourth trial (n = 2).
Only one subject of the wake group realized the mistake after
32 trials. There was no difference in the time point of realizing
the mistake between groups (P > 0.30).
Subjects in the sleep group showed normal sleep patterns
during the experimental night (total sleep time: 414.3 ± 14.2
min; stage 1 sleep [S1]: 19.7 ± 2.6 min; stage 2 sleep [S2]:
221.0 ± 10.4 min; SWS: 75.1 ± 4.9 min; and REM sleep: 75.6
± 5.6 min). Both groups spent the second night at home and
sleep time, and sleep quality (from 1 to 5 = “very poor” to “very
good”) was assessed by self-report. As expected, subjects in the
wake group slept longer during this night, thus compensating
for the sleep loss (520 ± 27 vs. 427 ± 19 min, P = 0.009); rated
sleep quality was comparable between groups (sleep: 4.41 ±
0.12, wake: 4.44 ± 0.12, P > 0.80).
Sleep and wake subjects were closely comparable in reaction
times ([in ms] sleep: initial session 318.1 ± 4.8, retest 327.8 ±
8.3; wake: initial session 330.8 ± 6.9, retest 332.6 ± 6.9) and
error rates (in %; sleep: initial session 5.1 ± 1.0, retest 2.9 ±
0.8; wake: initial session 7.4 ± 1.2, retest 4.5 ± 0.8), in actual
vigilance performance, and in self-reported general sleepiness
(sleep: initial session 2.4 ± 0.3, retest 2.2 ± 0.2; wake: initial session 2.2 ± 0.2, retest 2.5 ± 0.2) during the plan induction session
and at retesting (all P > 0.14). This, together with the fact that
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retrieval of the plan was tested only after a second night, which
allowed subjects in the wake condition to recover, excludes the
possibility that sleep deprivation confounded retrieval by general changes in attention. When asking the subjects in the end of
the experiment whether they actually remembered the instructed
intention, all of the subjects reported to recall the instruction,
excluding that those subjects who did not realize the mistake had
simply forgotten the instruction per se. An explorative analysis
of the questionnaire assessing rehearsal and strategies to remember the intention revealed that only 4 subjects used particular
strategies (e.g., imagining the colors of traffic lights). Subjects in
the sleep group reported that they had engaged in slightly more
rehearsal of the instruction than the wake group, particularly
during the day after the experimental night.
For those subjects who did not realize the mistake, the first 40
trials of the wrong version were analyzed. The vigilance task
duration of 5 min has been found to be sensitive to effects of
sleep deprivation and fatigue.7 Standard polysomnographic recordings included electroencephalogram (at C3 and C4), electrooculogram, and electromyogram. Recordings were visually
scored offline according to standard criteria.8
In the end of the retest session, subjects were debriefed about
the purpose of the experiment. Those subjects who did not realize that they were presented with the wrong task version during
retesting were asked by the experimenter whether they actually
remembered the instruction. Further, all subjects had to fill out
an explorative questionnaire assessing rehearsal of the instruction during the retention interval (i.e., in the evening after the
instruction, during the day after the experimental night, and in
the morning before the retest session) as well as the use of strategies to remember the instruction.
slow wave activity, and specific neurotransmitter constellations
(e.g., low levels of acetylcholine and cortisol).3 On the other
hand, these findings show that sleep does not simply passively
protect intentional memory traces against interfering inputs but
rather actively facilitates the maintenance of intentions. Particularly, to the sleep/wake comparison of Experiment 1, it could
be objected that subjects in the wake group were exposed to a
longer period of wakefulness during the retention interval, thus
experiencing a higher amount of interference that could have
disrupted the intentional memory. In Experiment 2, however,
subjects of the SWS-rich and REM-rich sleep groups were exposed to exactly the same amount of wakefulness and sleep during the retention interval, and thus external stimulus inputs were
completely comparable for both groups. The finding that, despite similar amounts of interfering inputs and protective sleep
periods, only subjects who obtained high amounts of SWS benefited from sleep, indicates that the benefit of sleep for intentions is not a passive protection against wake interference but
rather depends on active processes, particularly during SWS.5
The finding that the SWS-rich group outperformed the REMrich group in intention execution is even more striking when
considering that the SWS-rich group suffered from partial sleep
deprivation during the experimental night. The SWS-rich group
was allowed to sleep from 23:00 to 02:00 only and had to stay
awake thereafter, whereas the REM-rich group had an almost
normal night of sleep with only one forced wake period for the
plan induction session. The fact that a short sleep period containing high amounts of SWS can compensate even for the effects of
partial sleep deprivation underlines the potential importance of
SWS for the successful execution of delayed intentions.
Apart from a beneficial effect of sleep, rehearsal of the instructed intention might also have affected the likelihood of
executing the intention. One of the main characteristics of
prospective memory is that there are no prompts to execute
the intention, but rather the individual has to self-generate the
intention at the appropriate time. To manage this self-generation successfully, it might be important to keep the intention
active in mind over a longer time period. This can be effectively achieved, for example, by occasional self-reminding or
rehearsal of the intention. Although we have no conclusive data
on the use of rehearsal in the present study, our explorative
questionnaire on rehearsal of the instructed intention suggests
that subjects in the sleep group and subjects in the SWS-rich
sleep group might have rehearsed the instruction slightly more
than wake subjects and subjects of the REM-rich group. However, it remains unclear how these differences in rehearsal can
be interpreted. It could be speculated that active consolidation
processes in the sleep group and the SWS-rich group enhanced
the activation and availability of the intentional memory trace
thereby increasing the likelihood of spontaneous rehearsal. Alternatively, sleep deprivation in the wake group and circadian
differences in the time-point of encoding in the REM-rich group
might have impaired the ability or motivation for rehearsal of
the instruction. To clarify this issue, the possibility of rehearsal
as a factor influencing intention execution should be looked at
more closely in future studies using more elaborate measures to
assess rehearsal and self-reminding strategies.
Together, our results suggest that sleep, and particularly
SWS, can foster the implementation of intentions after a delay
DISCUSSION
Our findings show that sleep, and especially SWS, is important to keep future intentions active in memory. These findings
add to the literature on the role of sleep in memory consolidation by providing evidence that sleep does not only foster
consolidation of memories for the past3 and memories for the
future in a standard prospective memory task,6 but sleep can
also benefit the implementation of intentions in a relatively
naturalistic task. We assume that this consolidation during
sleep originates from reactivation of the representation during SWS that, aside from hippocampal networks,9 extend to
prefrontal cortex regions,10 specifically accommodating intentional aspects of the representation.
Intentions are typically thought of consisting of two aspects,
a prospective component (intent, to remember that something
has to be done) and a retrospective component (content, to remember what has to be done), both of which are necessary for
the successful implementation of an intention.2 We assume that
sleep benefits both the prospective and retrospective component. However, in the task reported here, we used an intention
with a rather “easy” retrospective component, i.e., to remember performing on the vigilance task with a different dot color.
Asking subjects after the experiment confirmed that all of the
subjects recalled the content of the instructed intention but had
simply failed to execute the intention at the appropriate time.
Thus, although we cannot fully exclude the possibility that
sleep had a subtle effect on the retrospective component as
well, the superior ability to implement the intention in sleep
subjects and subjects who obtained high amounts of SWS observed in the present study was probably the result of sleepdependent improvements in the prospective component. Future
studies will have to apply more complex prospective memory
tasks to disentangle the effect of sleep on the prospective and
retrospective aspects of intentions.
The finding that it is specifically SWS that benefits the execution of an intention is particularly important in two regards. On
the one hand, it suggests that the consolidation of intentional
memories might depend on physiological processes occurring
during SWS, such as hippocampal-neocortical reactivations,
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differ between groups (SWS-rich vs. REM-rich, sleep time: 519
± 22 vs. 475 ± 22 min, P > 0.17; sleep quality: 3.70 ± 0.37 vs.
4.27 ± 0.27, P > 0.20).
There was no difference between the groups in reaction times
([in ms] sleep: initial session 346.4 ± 11.7, retest 336.8 ± 10.6;
wake: initial session 353.4 ± 10.8, retest 339.8 ± 10.4) and error
rate (in %; sleep: initial session 4.3 ± 0.7, retest 5.0 ± 0.9; wake:
initial session 4.5 ± 0.7, retest 3.2 ± 0.6), in the vigilance task,
or in subjective sleepiness (sleep: initial session 2.3 ± 0.2, retest
2.1 ± 0.2; wake: initial session 2.0 ± 0.2, retest 2.1 ± 0.2) during
the initial session and at retesting (all P > 0.18). As in Experiment 1, asking the subjects for their memory of the instruction
in the end of the experiment confirmed that all of the subjects
recalled the instruction. Explorative analyses of the rehearsal/
strategy questionnaire revealed that none of the subjects used
particular strategies to remember the instruction, but subjects in
the SWS-rich group reported to have engaged in slightly more
rehearsal of the instruction, particularly before the retest session in the morning.
of two days. Such a mechanism might be highly adaptive in
everyday life where we are busily engaged in all kinds of activities while bearing in mind our lasting intentions. Considering
the importance of intentions and plans in coordinating everyday
life, our findings also give a clear idea of how devastating sleep
deprivation can be to efficient human daytime functioning.
ACKNOWLEDGMENTS
The authors thank Steffen Sauer and Roland Thele for help
with data collection.
DISCLOSURE STATEMENT
This work was supported by a grant from the Deutsche
Forschungsgemeinschaft (SFB 654 “Plasticity and sleep”). The
authors have indicated no financial conflicts of interest.
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