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An experiment analyzing sleep deprivation vs. sleep fragmentation.
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Sleep less or sleep in multiple short periods: a
neurocognitive analysis of sleep deprivation
in periods of required sustained wakefulness
Brendan Sheehan and Josh Garofolo
University of Waterloo
Abstract
There is an established link between sleep deprivation and neurocognitive deficits (Bonnet & Arand, 2003). When coupled with occupational environments requiring sustained vigilance these negative effects can pose a serious threat to equipment and personnel. Unfortunately due to budgetary or manpower limitations it is not always feasible to provide adequate sleep time within environments such as medicine and aviation(Armentrout et al, 2006). In the present study we asked whether a reorganized sleep architecture could allow an individual to attend to their duties as well as provide opportunities for sufficient rest. We compared two potential sleep regimens: partial sleep deprivation (PSD) and sleep fragmentation (SF). We defined PSD as 50% of the normal duration of a participant’s sleep and SF as the normal duration punctuated by four equidistance awakenings in which the participant had to complete 5min of simple mental tasks. We measured scores on a reverse digit span task, a psychomotor vigilance and mean HR while playing a non-violent video game. Our results favour sleep fragmentation as producing slightly fewer cognitive deficits.
Running Head: EFFECTS OF SLEEP FRAGMENTATION VS. PARTIAL SLEEP DEPRIVATION 1
Sleep less or sleep in multiple short periods: a neurocognitive analysis of sleep deprivation in periods of required sustained wakefulness ...the aircraft reached the beginning of the approach 2,800 feet too high and 35 knots too fast. Instead
of immediately correcting this the pilot continued to prepare the aircraft for landing. During preparations
neither pilot realized the flaps had not been set to the correct 100% setting and remained at 40%. As a result
the heavy C-5 Galaxy aircraft continued to both climb and decelerate. This unique combination often causes
an unrecognizable spatial disorientation in pilots (Armentrout, Holland, O’Toole & Ercoline, 2006). Both
pilots interpreted the instrumentation’s upward pitch warning as a malfunction. As the aircraft reached 4,900
feet it was at an upward angle of attack of over 30° and had an airspeed of just 55 knots. When the pilots
finally realized the dire condition the aircraft was in they began emergency maneuvers and did not regain
control until just over 773 feet above sea level (Armentrout et al., 2006).
This near fatal air crash was the subject of a 2006 US Air Force review. The aircraft was running a
long distance heavy-airlift mission from the eastern US to an island in the Indian Ocean. During incident
review researchers determined the culprit of the near-crash were not malfunctioning instruments but gross
pilot error. This is surprising as the aircrew included a third pilot and second flight engineer whose specific
roles encompassed redundant cross-checks. As well, each member of the five person crew was well-trained
and experienced in these types of flight missions. The researchers concluded that the host of pilot errors were
not due to incompetence but were secondary to extreme fatigue. The aircrew had been subject to almost a
week of modified sleep-wake cycles due to time zone shifts as well as changing departure times. On the
night of the mishap the crew had been on duty continuously for over 20h. The co-pilot reported, in 40h, just
6-8h of combined sleep. The authors indicated that if any of the pilots were more rested and alert the event
could have been avoided entirely (Armentrout et al, 2006).
The effects of sleep deprivation on humans are profound and diverse. After just a few hours of sleep
deprivation we become irritable and executive function tasks such as sustained concentration and mentation
EFFECTS OF SLEEP FRAGMENTATION VS. PARTIAL SLEEP DEPRIVATION 2
become increasingly difficult (Bonnet & Arand, 2003). Memory recall is reduced and incidences of false
memory recall increase (Diekelmann, Landolt, Lahl, Born & Wagner, 2008). Reaction times on vigilant
attention tasks slow and errors of both commission and omission increase (Lim & Dinges, 2008). These
negative effects get worse as humans endure consecutive nights of partial sleep deprivation. This
phenomenon has been referred to as the accumulation of a ‘sleep debt’ (Bonnet & Arand, 2003). An
individual who loses just three hours of sleep a night, for five consecutive nights, will perform as poorly as if
they had been awake for 33-48h continuously or had a blood alcohol content of 0.10% (Bonnet & Arand,
2003). The effects of chronic partial sleep deprivation1 are not limited to cognitive processes. One study
found six nights of partial sleep deprivation (at 4h of sleep/night) brought about harmful consequences to
carbohydrate metabolism and general endocrine functioning comparable to general physiological aging
(Spiegel, Leproult & Van Cauter, 1999).
Unfortunately there exist numerous situations which, by nature of the environment or inherent
processes, demand continued wakefulness from involved personnel. Medical students who have advanced to
the residency/intern level of their training are often expected to stay awake for periods exceeding 60 hours
during work/on-call schedules (Friedman, Kornfeld & Bigger, 1973). Fisherman aboard vessels engaged in
certain types of aggressive fishing techniques are routinely awake for over 24h continuously and may sleep
less than 1.5h in a 32h period (Gander, van den Berg & Signal, 2008). In the beginning example of the
fatigue-related mishap none of the aircrew was in violation of US Military flight regulations concerning time
on duty (Armentrout et al, 2006).
Of even greater concern is that occupations such as these demand a mix of required sustained
wakefulness as well as a level of cognitive resources not found in many other environments. Medical
EFFECTS OF SLEEP FRAGMENTATION VS. PARTIAL SLEEP DEPRIVATION 3
1 partial sleep deprivation is a reduction in the normal time spent continuously asleep; chronic (partial) sleep deprivation refers to multiple consecutive nights of partial sleep deprivation; sleep fragmentation is a normal-duration period asleep punctuated by various intervals of forced or spontaneous awakenings.
residents surveyed after one night without sleep are significantly more hostile and irritable (Samkoff &
Jacques, 1991); a deleterious attitude for an individual responsible for human care. In a review analyzing
higher-order executive functioning in sleep deprived military commanders Harrison and Horne (2000) found
numerous battle-relevant deficits such as impaired communication, unwarranted attention to peripheral
details and a reduced ability to cope with unexpected events (Harrison & Horne, 2000). The cockpit voice
recorder and instrument recording systems of the C-5 aircraft revealed the pilots exhibited almost all of these
negative cognitive behaviours. Indeed Wilson et al (2007) found sleep deprived aviators are slower to
recognize harmful systems deviations, become more unconsciously accepting of lower performance
standards and may even slip into uncontrollable micro-sleeps in-flight (Wilson, Caldwell & Russel, 2007).
Further exacerbating these situations are findings that sleep deprived individuals inaccurately assess their
own subjective sleepiness and may underestimate their actual level of fatigue (Bonnet & Arand, 2003). As
illustrated in the near-crash example, the outcome of sustained wakefulness coupled with occupations
requiring vigilant attention can be disastrous. As cited in Wadsworth et al (2006) 53% of fatal sea accidents
from grounding and 38% from vessel collisions are a result of “less alert lookouts” or “dozing off during
navigation” (Wadsworth, Allen, Wellens, McNamara & Smith, 2006, p. 837). Samkoff and Jacques (1991)
mention a New York grand jury which found the death of a female in 1984 partially due to the fatigued
residents whose care she was under (Samkoff & Jacques, 1991).
In this study we pragmatically accept that although these factors can precipitate dangerously altered
cognitive states the wakefulness demands of physicians, pilots and similar occupations will probably
continue to be governed by manpower/budget limitations. We ask, within the context of these occupations
requiring sustained wakefulness, are there particular sleeping arrangements that infer fewer cognitive
detriments? Perhaps instead of allotting a short period of time for sleep, where an individual's tasks must be
covered, the person could awaken at periodic intervals to attend to their duty. The end result would be a
EFFECTS OF SLEEP FRAGMENTATION VS. PARTIAL SLEEP DEPRIVATION 4
similar amount of available manpower across the activity’s duration (flight, sea voyage, etc.). The specifics
of the awakening schedule would of course depend on the individual work environments yet this is
conceivably feasible. Imagine a physician remaining at a hospital for 48h instead of returning home for short
periods of sleep whilst still on call. After completing their rounds they could be afforded a guaranteed hour
of uninterrupted rest at the hospital saving lost transit time. In the example of the near-crash perhaps the
third pilot could rotate in every 4h of flight time allowing one crew member 4h of uninterrupted rest.
The concept of normal duration sleep with periodic awakenings has been referred to as sleep
fragmentation. The largest body of research devoted to sleep fragmentation has centered around undesirable
spontaneous awakenings secondary to obstructive sleep apnea (OSA), periodic limb movement disorder
(Bonnet & Arand, 2003), external sensory stimuli (Stanchina, Abu-Hijleh, Chaudhry, Carlisle & Millman,
2005) and altered dream states such as sleep walking or night terrors (Aekerstedt et al, 2002). These studies
are similar to sleep deprivation experiments in that the principle variables of interest are objective and
subjective measures of alertness and cognitive functioning. The experiments will commonly awaken
participants in accordance with differing regimens and to various thresholds of arousal. Some studies will
utilize a strictly temporal regimen (i.e. awakening every 10min) while others awaken based on physiological
findings such as core temperature or specific EEG findings.
To examine sleep fragmentation under the guise of an occupational environment requiring sustained
wakefulness we had participants sleep in two baseline conditions and two experimental conditions: partial
sleep deprivation and sleep fragmentation. We then assessed the participants on cognitive measures, a
reverse digit span task (RDST) and a psychomotor vigilance task (PVT), as well as physiological measures,
heart rate changes during a stressful non-violent video game.
EFFECTS OF SLEEP FRAGMENTATION VS. PARTIAL SLEEP DEPRIVATION 5
Method
Participants
Research participants were two males aged 23 and 24 years old. Both were undergraduate students at
the University of Waterloo, Waterloo, Ontario. Neither participant reported any history of cardiovascular or
respiratory disease. Participants were selected as part of a third year research methods course in human
cognitive neuroscience.
Design
This experiment was a within-subjects design comparing baseline performance with both sleep
fragmentation and partial sleep deprivation. As illustrated in Figure 1, this study was conducted in an ABBA
format with a baseline session both before and after the experimental sessions. Both study participants
underwent both experimental sleep conditions and were assigned in an opposing fashion to reduce any order
effect. All sessions were at least 24 hours apart to reduce any carry over effect.
Figure 1: Study baseline and experimental session organization
Test Instruments and Measures
Cognitive performance measures were the reverse digit span task (RDST) and the psychomotor
vigilance task (PVT). The reverse digit span task is a measure of executive planning and sequential
processing (Schofield & Ashman, 1986). Participants are instructed to focus intently on remembering a list
of randomly generated single digits read aloud by an experimenter. While holding the number sequence in,
presumably, their working memory the participants then mentally reverse the sequence and record these
numbers on a provided sheet. Our sequence began with two digits (i.e. 2,3) and progressed to nine digits. We
presented two sequences at each level (i.e. 2,3 then 5,6) for a total of sixteen trials. Our measures of outcome
EFFECTS OF SLEEP FRAGMENTATION VS. PARTIAL SLEEP DEPRIVATION 6
Night 1 Night 2 Night 3 Night 4
Participant 1 Baseline 1 Sleep fragmentation Sleep deprivation Baseline 2
Participant 2 Baseline 1 Sleep deprivation Sleep fragmentation Baseline 2
were total number of erroneous trials and highest level achieved (i.e. a correct seven-digit sequence would be
level seven). The PVT is widely regarded as one of the most accurate tests to assess vigilance and attention
within sleep augmentation experiments (Lim & Dinges, 2008). Participants are instructed to fixate on a cross
and await a stimuli that will appear at either the left or right side of the screen. The interval between trial
commencement and stimuli presentation randomly fluctuates between two and ten seconds in one second
intervals: termed the inter-stimuli interval (ISI). Upon stimuli presentation the participant must hit one of
two pre-defined keys corresponding to the side the stimuli was presented on. The PVT provides multiple
results available for tracking within an experiment. We selected mean reaction time (RT) and errors of
commission (incorrect side selection). We did not analyze errors of omission (a failure to respond) as studies
have shown it takes four to five days of consecutive partial sleep deprivation for participants to score
differently than controls (Lim & Dinges, 2008).
Physiological measure was average heart rate (HR) while playing the two-dimensional non-violent
video game Vector Runner. We selected Vector Runner in accordance with the criteria Turner et al (1983)
outlined such as the elements of “uncertainty and avoidance” (Turner, Carroll & Courtney, 1983, p. 545).
The participant steers the icon of a spaceship to the left or right with keyboard arrow keys to avoid objects
and pick up extra-points markers. The participant has no control over the speed of the spaceship and the
game automatically accelerates at fixed intervals. Scoring is based on time elapsed during play as well as the
extra-points markers. An additional benefit to using a game such as Vector Runner is that it requires only
minor torso movement and skeletal muscle involvement which aides in artifact reduction. For each session
we recorded a 120s acclimatization epoch followed by a 120s gaming epoch. Our measures of outcome were
high score achieved and mean HR scores. In addition to the above variables we did record measures of heart
rate variability (HRV) utilizing a separate three-electrode component of our physiological recording
apparatus. There is a growing and very interesting body of research in psychology that is analyzing HRV
EFFECTS OF SLEEP FRAGMENTATION VS. PARTIAL SLEEP DEPRIVATION 7
data. Although we spent some time analyzing these data a thorough and acceptable review was beyond the
scope of this project.
Apparatus
Reverse digit span task was conducted with prompts from the SuperLab 4.0 stimulus presentation
software program (Cedrus Corporation, San Pedro, CA). When prompted by SuperLab experimenters would
read aloud a pre-made list of random numbers. The digit sequences were randomly generated using the
RAND function of Microsoft Excel (Microsoft Corporation, Redmond, WA). Participants recorded their
responses on paper which were later marked by the experimenter.
Psychomotor Vigilance Task (PVT) was also administered with the SuperLab 4.0 stimulus
presentation software program. We programmed an experiment which would present the fixation cross and
then a randomized left or right stimuli at random 2-10s ISI. Participant responses were recorded on a Cedrus
RB series response pad (rb-x30; Cedrus Corporation, San Pedro, CA).
Heart rate response data were recorded using an MLT1010 pulse transducer amplified by the
Powerlab Psychophysiology Data Acquisition System. The pulse transducer was affixed to the index finger
of the participant’s non-dominant hand. Digital signals were recorded by Chart 7.0 software. The MLT1010
pulse transducer records heart rate activity. The Powerlab software is a data acquisition system that amplifies
analog signals from transducers and converts them into digital signals. The Chart 7.0 software transforms the
digital signal from Powerlab into a recognizable trace which allows heart waveforms to be detected. Chart
7.0 also saves data to facilitate post-processing. Powerlab sampled heart rate at 1,000 times per second. We
recorded HR in 120s epochs for both the acclimatization and experimental conditions. If any movement
artifacts were present they were removed during post-processing. R-waves were detected using the
“Cardiovascular - Finger Pulse transducer” option within the detection settings on the Chart 7.0 system. We
adjusted the minimum peak height, as a function of number of standard deviations, to detect r-waves. We
EFFECTS OF SLEEP FRAGMENTATION VS. PARTIAL SLEEP DEPRIVATION 8
used the Chart 7.0 system to detect individual local maxima’s then labelled them as R-waves. We created a
Macro to speed up the process and individually labelled each R-wave skipping over the movement artifact
section. The Vector Runner game was played online through the Firefox browser on a Macintosh iMac
computer. Game input was afforded by a standard USB keyboard’s left and right arrow keys.
Experimental regulation was provided by brief sleep diaries used throughout the study to track time
in bed as well as experimental compliance. Standard digital alarm clocks already in the participant’s home
were use to regulate waking times and provide arousal stimuli.
Procedure
As individual sleep habits differ considerably (Ferrara & De Gennaro, 2001) we based the temporal
regimens of the experimental conditions on the participant’s respective sleep habits. Normal sleep duration
was defined as, for the first baseline night, the interval between lights-off attempting to sleep and lights-on
getting out of bed. A priori we declared any spontaneous awakenings (i.e. bathroom, etc.) shorter than 5min
duration part of normal sleep hygiene and did require participants to record them. The temporal regimen for
the experimental conditions was set a priori and was as follows.
Sleep deprivation was defined as 50% of the normal sleep duration. For example if the participant’s
baseline sleep duration was 8h they would remain awake 4h later than normal. The participant would then
begin lights-off attempting to sleep and awaken at their normal time 4h later. We utilized this arrangement
(as opposed to sleeping the first 4h) to attempt to control for any sleep inertia effects during testing.
Sleep fragmentation consisted of lights-off 20 minutes prior to the participant’s normal time in bed
(to accommodate the 4 intervals). Sleep was of normal duration and punctuated by four equidistance
awakenings. For example if the participant’s normal sleep duration was 8h they would awaken every 2h.
During the sleep fragmentation condition the participants had to awaken (in response to their alarm clock)
turn on the lights and complete 5 minutes of a quiet mental activity (math problems, sudoku).
EFFECTS OF SLEEP FRAGMENTATION VS. PARTIAL SLEEP DEPRIVATION 9
Results
The individual sleep data are presented for each participant in Table 1. Each subject complied with
the protocols of the study. Participant 2 reported a habitual normal sleep duration of 6h. As afore mentioned,
in an effort to control for sleep inertia, all conditions were arranged temporally so as to submit participants to
testing within the same 2h interval after waking.
Table 1: Sleeping Data
Our overall findings are summarized in Table 2. We found the sleep deprivation condition resulted in
poorer scores on the RDST, slower reaction times on the PVT and lower high scores in the Vector Runner.
Figure 2 illustrates the poorer sleep deprivation scores on the RDST as well as an overall lower level
achieved for both experimental conditions. As shown in Figure 3 RTs were relatively consistent except for a
slight increase in the sleep deprivation condition.
0
2
4
5
7
Baseline 1 Sleep Dep Sleep Frag Baseline 2
6
7
8
9
Figure 2: Reverse digit span task
0
123
245
368
490
Baseline 1 Sleep Dep Sleep Frag Baseline 2
0
0.75
1.50
2.25
3.00
Figure 3: Psychomotor vigilance task
RT (ms) No of errorsNo of errors Highest level
EFFECTS OF SLEEP FRAGMENTATION VS. PARTIAL SLEEP DEPRIVATION 10
Normal SleepDuration
Fragmented SleepDuration
Interval length
Sleep DeprivationDuration
Participant 1 8 h 8 h 2 h 4 h
Participant 2 6 h 6 h 1.5 h 3 h
Figure 4 shows the slight decrease in mean high scores for the sleep deprivation condition. Also
depicted are the average HR, in bpm, for both the 120s acclimatization epochs and the 120s gaming epochs.
We were surprised to find our HR results opposed those of similar studies (Turner et al, 1983). Instead of
increasing, our mean HR decreased, during the gaming epochs by an average of 1.6 bpm.
Table 2: Experimental ResultsBaseline
1Sleep
DeprivationSleep
FragmentationBaseline 2
Reverse Digit Span TaskReverse Digit Span TaskReverse Digit Span TaskReverse Digit Span Task
No of errors 4.5 6.5 5 4
Highest level achieved 7.5 7 7 8
Psychomotor Vigilance Task (PVT)Psychomotor Vigilance Task (PVT)Psychomotor Vigilance Task (PVT)Psychomotor Vigilance Task (PVT)
Mean RT 401.14 486.974 433.92 434.705
No of errors 1 1 2.5 2
Vector RunnerVector RunnerVector RunnerVector Runner
High Score 9147 8158.5 9369 11559
Mean HR* in acclimatization 71.24 70.20 69.24 68.08
Mean HR* in gaming 66.83 69.63 68.20 67.45
N=2, * in beats per minute (bpm)
66
68
69
71
72
Baseline1 Deprived Fragmented Baseline2
0
3000
6000
9000
12000
Figure 4: Vector Runner
Avg. HR Acc Avg. HR Game High Score
EFFECTS OF SLEEP FRAGMENTATION VS. PARTIAL SLEEP DEPRIVATION 11
Discussion
In this study we asked, in the context of an occupational environment requiring sustained
wakefulness, are there particular sleeping arrangements that incur fewer cognitive detriments? We recorded
scores on reverse digit span tasks, psychomotor vigilance tasks and average HR while playing a video game
after two baseline and two experimental augmented sleep pattern sessions. Our results indicate slightly
poorer scores after a night of partial sleep deprivation on RDST, PVT and video game high scores when
compared with a night of sleep fragmentation and baseline nights. Overall, these data favour the sleep
fragmentation model as producing fewer negative cognitive effects.
We feel our smaller sample size may have affected our results. Besides the obvious statistical power
reductions from such a small sample size (N=2), we felt a larger sample group would help to reduce the vast
inter-participant variability. While one of our participants reported healthy sleep hygiene the other
participant reported habitually sleeping less than 6h per night for over three years. Indeed Bonnet and Arand
(2003) described a few sleep deprivation studies that found higher performance levels in post-experimental
recovery sessions than in initial baseline recordings. This suggests the participants were arriving at the sleep
lab with some level of sleep debt which they then slept off under a monitored 8h in bed (Bonnet & Arand,
2003). Some authors do include a pre-study phase in experiments which ensures normal sleep hygiene (ex.
Bonnet, 1989) but we feel this would detract from the generalizability of our findings. It is estimated that
20% to 40% of the US adult population sleeps less than 7h a night on weeknights (Basner & Dinges, 2009)
and thus forcing participants to sleep 8h may affect the strength of our findings. Because of these issues
when considering future research we feel the best course would be to rely on random selection and larger
sample sizes.
A discordance we must address is that our finding, that sleep fragmentation is less detrimental than
sleep deprivation, is unexpected when considering studies that have found no difference in cognitive
EFFECTS OF SLEEP FRAGMENTATION VS. PARTIAL SLEEP DEPRIVATION 12
detriments. Bonnet and Arand (2003) reviewed the literature and found numerous studies linking sleep
fragmentation with poor outcomes such as negative mood affect. They also found that 13 out of 14 studies
found sleep fragmentation to cause increases in subjective ratings of sleepiness (Bonnet & Arand, 2003).
One explanation for this disagreement could be that many of these studies were designed to simulate
undesirable spontaneous awakenings such as those common in patients suffering from obstructive sleep
apnea (OSA) or periodic limb movement disorder (PLMD). When not viewed in the context of OSA or
PLMD these studies seem bizarre and unrealistic. Healthy participants are commonly awoken at intervals
such as every ten minutes, every five minutes, and in some cases even as often as every 60 seconds
(Stepanski, 2002). Anecdotally it would be difficult to predict any rest at all whilst receiving an audible tone
every minute for eight hours. The participants in our study were awoken once every 1.5-2h respective of
their normal sleeping habits. It is conceivable that the temporal frequency of the fragmentation moderates
the effects on cognitive performance. We did find one study that assessed cognitive function after sleep
fragmentation in intervals of 1min, 10min and 2.5h (Bonnet, 1986). Their results are supportive of our
assertion that sleep fragmentation interacts with frequency of arousal as the 2.5h participants scored the best.
As the digital age continues to transform our society and the performance expectations gap between
day and night shrinks further the demands placed upon our 24h circadian rhythms will surely continue to
increase. Many individuals are already willingly limiting themselves to less than healthy levels of sleep for
occupational and/or social purposes (Basner & Dinges, 2009). As we have illustrated this exchange comes at
a price. Not only in the acute reduction of an individual’s abilities and performance but also in chronic
threats to health and safety. Research has found employees who routinely do not recover from occupationally
induced fatigue are more likely to report feelings of being overwhelmed and of general ill health (Wadsworth
et al., 2006). Examples of fatigue related accidents such as the US Air Force near-crash are numerous and
occur in a diverse range of job environments. Unfortunately, as the authors of that study noted in their
EFFECTS OF SLEEP FRAGMENTATION VS. PARTIAL SLEEP DEPRIVATION 13
conclusion, little progress has been made to prevent these circumstances from arising again (Armentrout et
al, 2006). It is our hope that with a continued pragmatic approach and a focus on applied empirical research
an effective sleep architecture will be determined. One that will satisfy ever-increasing operational demands
in fields such as medicine and aviation and also ensure the individuals involved are adequately recovering
and maintaing a safe level of cognitive resources.
EFFECTS OF SLEEP FRAGMENTATION VS. PARTIAL SLEEP DEPRIVATION 14
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