Physiological arousal and attention during a week of continuous sleep restriction Physiology ...

12 Pages·2008·0.67 MB·English

Physiology&Behavior95(2008)353–364
ContentslistsavailableatScienceDirect
Physiology & Behavior
journal homepage: www.elsevier.com/locate/phb
Physiological arousal and attention during a week of continuous sleep restriction
⁎
Kimberly A. Cote , Catherine E. Milner, Stephanie L. Osip, Meghan L. Baker, Brielle P. Cuthbert
PsychologyDepartment,BrockUniversity,St.Catharines,Canada
A R T I C L E I N F O A B S T R A C T
Articlehistory: Wakingbrainphysiologyunderlyingdeficitsfromcontinuoussleeprestriction(CSR)isnotwellunderstood.
Received25January2008 Fourteengoodsleepersparticipatedina21-dayprotocolwheretheyslepttheirusualamountinabaseline
Receivedinrevisedform30May2008 week,hadtheirtimeinbedrestrictedby33%inaCSRweek,andsleptthedesiredamountinarecovery
Accepted27June2008
week.Participantssleptathome,completingdiaries andwearingactivitymonitorstoverifycompliance.
Each day participants completed an RT task and mood and sleepiness ratings every 3 h. Laboratory
Keywords:
assessmentofelectrophysiologyandperformancetookplaceattheendofbaseline,threetimesthroughout
Sleeprestriction
the CSR week, and at the beginning of recovery. Participants reported less sleep during CSR which was
Sleepiness
Performance confirmed by activity monitors. Correspondingly, well-being and neurobehavioural performance was
EEG impaired.QuantitativeEEGanalysisrevealedsignificantlyreducedarousalbetweenthe1stand7thdaysof
Spectralanalysis restrictionandlineareffectsatanteriorsites(Fp2,Fz,F8,T8).Atposteriorsites(P4,P8),reductionsoccurred
Event-relatedpotentials onlylaterintheweekbetweenthe4thand7thnightsofrestriction.Boththeimmediatelineardeclinein
arousalandprecipitousdroplaterintheweekwereapparentatcentralsites(C4,Cz).Thus,frontalregions
were affected immediately, while parietal regions showed maintenance of function until restrictionwas
moresevere.TheP300ERPcomponentshowedevidenceofreducedattentionbythe7thdayofrestriction(at
Pz, P4). EEG and ERPs deficits were more robust in the right-hemisphere, which may reflect greater
vulnerabilitytosleeplossinthenon-dominanthemisphere.
©2008PublishedbyElsevierInc.
Totalsleepdeprivationinhumans(greaterthan24hofwakeful- researchusingimaging,EEG,orERPtechniquestoexaminetheneural
ness)hasbeenwidelystudiedformorethanacentury[1].Theeffects basisofperformancedeficitsduringsleeplosshasbeendoneunder
onmoodandperformance,aswellascharacteristicsknowntomask extremeconditionsoftotalsleepdeprivation.Theaimofthepresent
deficits,havebeenwelldescribed[2–6];however,thenatureofbrain study was to investigate waking brain function during continuous
functioning underlying these behavioural changes remains poorly sleeprestriction.
understood. It has been proposed that the deficits observed during There are a number of reports on waking EEG characteristics
sleepdeprivationmayinvolvefrontallobeimpairmentinparticular following total sleep deprivation [16–24]. There are some incon-
[7]. Consistent with this notion, many brain imaging studies have sistencies in outcome, likely due to differences in methods (e.g.,
shown reduced activity in prefrontal cortex following total sleep timingofrecording,lengthofsleepdeprivation,recordingduringeyes
deprivation[8–12].However,anumberofimagingstudieshavealso opened or closed) and analysis techniques (e.g., amount of EEG
shown increased activity in the frontal regions [13,14]. Drummond processed, reporting relative or absolute power, definition of
and Brown suggested that these regional patterns of activation and frequency bands).For instance,some havereported that total sleep
deactivation may be dependent on the nature of the specific task deprivationleadstoincreasedpowerinlowerfrequencies(e.g.,alpha
performed,andthatthebrainmaybecapableofcompensationduring and theta), when recorded at rest (eyes opened) or during task
sleep loss [15]. EEG and event-related potentials (ERPs) are neuro- performance[16,19,20].However,alphaistypicallylowerwhensleepy
physiological measures of arousal and information processing that ifrecordedwitheyesclosed[22],similartowhatisseenduringsleep
mayalsobeusedtoinvestigatetheCNSnatureofperformanceduring onset.Giventhatalphaisnormallyblockedwhentheeyesareopened,
sleepiness. They have greater time resolution than fMRI imaging recordingitwhileeyesareclosedislikelyamoresensitivemeasureof
techniques. Specifically, the timing of cognitive processes can be changesinalphaandthusthebestmetricofsleepiness.Theincreases
determined in the order of milliseconds using ERPs, while EEG in theta have been shown to be correlated with reaction time (RT)
providesacontinuousmeasureofarousalovertime.Muchoftheprior slowing[22]andsubjectivesleepinessreports[16,21,24].Alphaand
thetaEEGinwakefulnessarethusmarkersofCNSarousalwhichare
thoughttoreflectahomeostaticprocesssimilartothereboundofslow
⁎ Corresponding author. Brock University Sleep Research Laboratory, Psychology
wavesleepfollowingsleepdeprivation[17,25].Therehavealsobeena
Department,BrockUniversity,St.Catharines,Ontario,CanadaL2S3A1.Tel.:[phone]
numberofreportsofincreasedhighfrequencyEEGinthebetarange
5550x4806;fax:[phone].
E-mailaddress:[email protected](K.A.Cote). (e.g.,typically16–40Hz)followingtotalsleepdeprivationwhichhas
0031-9384/$–seefrontmatter©2008PublishedbyElsevierInc.
doi:10.1016/j.physbeh.2008.06.016
354 K.A.Coteetal./Physiology&Behavior95(2008)353–364
been interpreted as increased effort [18–20,22]. A fewstudies have sleepinessandfatigue,anddeficitsinmoodandperformance“lapses”.
attemptedtolocalizethescalptopographyoftheseeffects.Cajochen More recently, two separate groups published the results of dose–
et al. reported that the increased power in theta band was responseinvestigationsofcumulativesleeprestriction.VanDongenet
predominant at frontal sites [17]. Similarly, Forest and Godbout al.manipulatedsleeptimebyreducingtimeinbedforthreeseparate
observedtheincreasedthetaatfrontalandtemporalsites,aswellas groupsto4,6,and8hover14days[42],whileBelenkyetal.didsoby
increased beta at frontal sites, following one night of total sleep reducingtimeinbedforfourgroupsto3,5,7,and9hover7days[39].
deprivation[26].Ferreiraetal.recentlyreporteddecreasesinabsolute In both studies, sleep restriction was compared to baseline and
power of alpha apparent in frontal, temporal and occipital regions, recovery conditions within subjects. Van Dongen et al. reported
decreases in absolute power of beta in the temporal region, and cumulativedeficitsonbehaviouraltasksacrossthe14daysinthe4-
increases in relative power of theta and delta in the occipital and and6-hoursleepgroups.Similarly,Belenkyetal.reportedcontinuous
temporal areas following one night of sleep deprivation [27]. The deficitsinthemostseverelyrestrictedgroup(3-hrsleepers).Inthe5-
authorsproposedthatthesite-specificeffectsmightreflectregional and 7-hour groups, however, they reported an initial drop in
areasofbrainadaptation. performancefollowedbystablebutreducedperformancefor7days
ERPs have been investigated following total sleep deprivation ofrestriction.Belenkyetal.thereforeconcludedthatthebrainmay
using oddball paradigms to elicit long-latency ERPs such as N1-P2- adapt to this level of sleep restriction over time. Although these
P300whichreflectvariousstagesofinformationprocessing.Anearly studies are inconsistent with respect to the cumulative nature of
negative wave called N1 is considered mesogenous; that is, it is impairment from continuous sleep restriction, they do provide
exogenous in nature because it is sensitive to changes in physical support for dose-dependent effects of sleep restriction on perfor-
parameters of the stimulus (and thus reflects early sensory proces- mance of behavioural tasks. Neither study provided data on the
sing), yet it is endogenous in nature because it changes with associatedwakingbrainphysiology.ExaminingEEG/ERPsinwakeful-
manipulations to attention (i.e., N1 is reduced when attention is ness coincident with behavioural performance will lead to a better
reduced due to the removal of a long-lasting negative wave, called understanding of the nature of brain functioning during sleep loss.
Processing Negativity (PN), which overlaps in time and summates Thesetechniquesmayalsobeusedtodetermineifthebrainiscapable
withN1)[28].DelaysinN1latencyhavebeenreportedfollowingtotal ofadaptivechangeorcompensationinordertomaintainperformance
sleepdeprivation[29,30];thesechangesmayreflectslowedsensory duringsleeploss.
encodingprocessesordelaysinattentionalprocessesduetoPN.P300 ThestudybyBrunnerandcolleaguesisuniqueinreportingwaking
is an endogenous ERP component that is altered by changes in EEG changes following continuous sleep restriction paradigm [40].
attention [28]. Both delayed latency and reduced amplitude of the Theauthorsreporteddecreasedalpha(9.25–10Hz)followingthe2nd
P300 component have been reported using auditory oddball para- night of restriction and increased delta (3.75–4.5 Hz) after the 4th
digms [31–34]. Thesedata indicate that total sleep deprivation also nightofrestrictionintheeyesopenedcondition.Intheeyesclosed
affects later, more complex, stages of information processing. condition,alphadecreasedanddeltaincreasedafterthe3rdand4th
Specifically, these alterations to P300 reflect delays in the time nights of restriction. These waking EEG data showed a pattern of
takentodiscriminatetargetfromnon-targetstimuli,andimpairment brainwave synchronization similar to what was observed in the
in the degree of attention that is allocated to the task [35]. Corsi- nocturnalsleepepisode.TheinterpretationofthewakingEEGdatain
Cabrera et al. reported reduced amplitudes in late components this study is limited by the amount of data recorded (e.g., a single
(ranging from 180 ms to 718 ms) following 40 h of total sleep recordingsessionat07:15,for3min,fromeithertheC3orC4site)and
deprivation using a visual ERP paradigm [36]. The reductions in thehighdegreeofinter-subjectvariabilitythatresulted.Inthedose–
amplitude were correlated with RT slowing and increased alpha/ response study of sleep restriction by VanDongen et al. [42], they
theta/betaEEGpowerinthepre-stimulusinterval,suggestingarole foundnoprogressivechangesinalphaorthetaEEGoverthe2week
forattentionalmechanismsintheoft-reporteddeficitsinperformance period of sleep restriction [43]. Again, the small amount of data
and arousal. The aforementioned studies applied either a single collectedfromasingleelectrodeduringa5-minuterecordingsession
electrode or three midline sites for analysis of ERPs. Based on a inasubsetofonly6participantspergroupmayexplainthelackof
recording from five scalp sites, Kaneda et al. reported that P300 sensitivityintheEEGmeasure.
latency was delayed at fronto-central sites while amplitude was AlthoughtherearenoreportsofERPsfollowingsleeprestriction,
reducedcentrally[37].Recently,Gosselinetal.showedthat36hof twostudieshaveexaminedinformationprocessingfollowingexperi-
wakefulness affected the amplitude of a frontally driven ‘novel P3’ mentallyinducedsleepfragmentation[44,45].Coteetal.reportedthat
component[38].Thesedatashowthataspecifictypeofinformation twonightsoffragmentationledtoimpairmentinarousalandearly
processingwhichislocalizedtofrontalbrainregions,namelynovelty encodingprocessesreflectedintheN1componentoftheauditoryERP
processing,iscompromisedbysleeploss. [44].NochangeswereobservedforthelaterP300waveform.Usinga
Waking EEG, ERP, and imaging data [7,15] reveal that there are visual ERP paradigm, however, Kingshott et al. found reductions in
changes in CNS function that underlie deficits in performance amplitude of the later P300 component that were apparent at
following total sleep deprivation. It is also important to investigate widespread locations across the scalp [45]. Together, these studies
the impact of a degree of sleep loss that is more commonly show deficits in information processing following a subtle level of
experiencedintherealworld.Partiallyrestrictingsleeptime(e.g.,to sleep disruption which were apparent in electrophysiological mea-
4or6hpernight)hasbeenshowntoaffecttheEEGcharacteristicsof sureswhennobehaviouralperformancedeficitcouldbeobserved.
sleep[39,40].Specifically,Brunneretal.andBelenkyetal.reported In the present study, physiological arousal and attention were
decreased amounts of Stages 1, 2 and REM sleep throughout the investigatedusingquantitativeelectrophysiologicalmethods,EEGand
course of sleep restriction. Brunner et al. further showed that the ERPs, during a week of continuous sleep restriction. In a 21-day
patternofdeltapower(.75–4.5Hz)duringnon-REMsleepincreased protocol (one week of baseline, one week of sleep restriction, one
overfourconsecutivenightsofrestriction,demonstratingthatsleep weekofrecovery),participantscompletedsleepdiaries,woreactivity
pressureincreasesacrosscontinuousnightsofsleeprestriction. monitorsandperformedregularlyscheduledRTtaskswhileathome.
The behavioural effects of sleep restriction on waking function Visits to the laboratory for assessment of electrophysiology and
have beenwell studied in recent years. Dinges et al. demonstrated performancetookplaceonthemorningofDay7(following7thnight
cumulativedeficitsonarangeofbehavioraltasksduringcontinuous of baseline), Day8 (following 1st night of restricted sleep), Day11
sleeprestriction[41].Theyreportedthatsleeprestrictedby33%below (following4thnightofrestrictedsleep),Day14(following7thnightof
habitualamountsoveraone-weekperiodledtoalinearincreasein restricted sleep),andDay15 (following 1st nightofrecovery). Sleep
K.A.Coteetal./Physiology&Behavior95(2008)353–364 355
wasrestricted at home in ordertostudy individualsovera 3-week underwentPSGscreeninginthelaboratory,4wereneverenrolledin
periodunderconditionsmoreecologicallyvalidthanthelaboratory theremainderofthestudyduetoschedulingincompatibilities,1was
setting where long-term study is problematic. Given that the excluded due to lost data from technical difficulties, and 8 were
behavioural profile of sleep restriction has beenwell established in withdrawnduetolackofinterestorfailuretocomplywiththestudy
systematic laboratory studies, it is timely that researchers begin to procedures.Specifically,6withdrewduringthebaselineweek(3male,
examine the effects of sleep loss outside the laboratory. There is a 3 female) because they found the study procedures to be too
paucity of studies that systematically compare home-based and demanding (e.g., RT task 5 times per day). Two male participants
laboratorystudiesofsleeprestriction.Inordertoensurethereliability werelostduringthesleeprestrictionweek;onewithdrewbecausethe
of home data, careful instructions were given and compliance was protocol was “too difficult” and the other was removed by experi-
verified.Basedonpreviousbehaviouralresearch,itwashypothesized mentersduetonon-complianceforcompletingtasksandforfailureto
thatthisdegreeofsleeprestrictionwouldleadtodeficitsinmoodand arrivetothelaboratoryontime.
performance (e.g., on RT). In addition, it was hypothesized that Theremaining14participantscompletedthe3-weekprotocol(2
systematic changes inphysiological arousal and attentionwould be males; mean age=20.86, SD=2.57). Participants were paid $150 for
associated with sleep restriction. A multiple-channel EEG recording completionoftheprotocol.Participantswhowithdrewfromthestudy
approachwastakeninordertoinvestigatehowregionalbrainactivity orwhowereremovedbytheresearchersduetonon-compliancewere
changedoverthecourseofsleeprestriction. paid a prorated amount. The Research Ethics Board of the local
Universityapprovedallstudyprocedures.
1.Methods
1.2.Procedure
1.1.Participants
Theprotocollasted21consecutivedaysandnights(refertoFig.1
Participantswererecruitedviaadvertisementsplacedaroundthe for an illustration of the protocol). Participants were instructed to
local university and in the community. Participants meeting the maintainaregularsleep–wakescheduleforthefirstweek,weresleep
following criteria were invited to contact the Sleep Research restrictedduringthesecondweek,andwereallowedtoreturntotheir
Laboratory: 18 to 35 years old, healthy, good sleeper, right-handed, regularsleepingscheduleforthethirdweek.Forthedurationofthe
non-smoker, and free from medications. In a telephone interview, study, participants were instructed to refrain from napping, to
participantswerefurtherscreenedtoensurethattheyhadaregular minimize alcohol consumption, and to keep caffeine consumption
sleep/wake schedule, typically consumed less than 1–2 caffeinated constantatpre-studylevels(note:participantswererecruitedtobe
beverages per day, were fluent in English, and had no history of minimal caffeine users). For example, participants were allowed to
depression, heart disease, neurological disease, or chronic pain. consumetheirusualmorningcoffee.Thepurposeofallowingminimal,
Appropriate candidates were invited to an orientation session and but usual amounts of caffeine was to collect data from a more
tourofthelaboratory.Aftersigningconsent,theyweregivenahearing naturalistic sample, avoid caffeine withdrawal, and ensure that
testtoensure that theirhearing was within an acceptable level for participationwasnottooonerousinthelengthyprotocol.Ondaysin
auditoryERPtasks(i.e.,below15dBat500,1000,1500,and2000Hzin which participants were scheduled to have in-laboratory testing of
bothears),andcompletedquestionnairesonsleephistoryandhabits, EEG/ERPs,theywereinstructedtorefrainfromdrinkingcaffeineprior
morningness–eveningnesschronotype,personality,mood,andhealth. to the 9 am testing session. This ensured that electrophysiological
Candidates then underwent a single night of standard polysomno- measures would not be confounded by individual differences in
graphic assessment in the Sleep Research Laboratory (e.g., signals caffeineconsumptionandsensitivity,oracuteenhancementofarousal
recordedfromC3/C4EEGsites,aleftandrightEOG,andasubmental duetomorningcaffeineintake.Dailydiariesofcaffeineconsumption
EMGtoidentifysleepstages).Measuresalsoincludedabdominaland showednostatisticaldifferencebetweenthe3-weekstudyconditions,
thoracic respirationwith effort bands and leg EMG with electrodes andverifiedtherestrictionofcaffeinepriortoin-laboratorytesting.
placedovertheanteriortibialisofeachlegtoscreenforsleep-related
respiratoryandmovementdisorders.Noparticipantswereremoved 1.2.1.Pre-studytraining
atthisstageonthebasisofclinicalevidenceofsleepapneaorperiodic Participantscametothelaboratoryonthedayprecedingtheirfirst
limb-movements (i.e., b5 events/h). Of the 61 participants initially dayinthe21-daystudy.Theyweregivenallequipmentneededforthe
volunteering to participate, 18 were eliminated following the at-homeprocedures,includinganactigraph(IMSystemsInc),reaction
telephone interview and 16 were eliminated following orientation timedeviceandcharger,sleep-activitydiary,andastudyinstruction
due to exclusion criteria or inability to schedule. Of the 27 who log.Reactiontimewascollectedusingahand-heldelectronicdevice
Fig.1.Illustrationof21-dayprotocol.Thelevelofinactivity(“sleep”)isillustratedacrossthe21daysoftheprotocol,whereparticipantsslepttheirusualamountinweek1(baseline),
wereinstructedtocurtailtheirsleepby33%inweek2(restriction),andsleptasdesiredinweek3(recovery).Notethedecreaseintimespentinactiveduringtherestrictionphase,
andthereboundorincreaseintimespentinactiveduringrecovery.LaboratoryassessmentofEEG,ERPs,andperformancewasdoneonDay7(following7thnightofbaseline),Day8
(following1stnightofrestrictedsleep),Day11(following4thnightofrestrictedsleep),Day14(following7thnightofrestrictedsleep),andDay15(following1stnightofrecovery).
356 K.A.Coteetal./Physiology&Behavior95(2008)353–364
that was custom built in the laboratory. Data was displayed to the recordedduringa45minPABthatwasadministeredonacomputer
participantonascreen,andresponsesweremadeusingbuttonswith locatedinthebedroomusingE-Primesoftware(PsychologySoftware
the right or left hand. A computer was used to pre-program the Tools Inc). Participants began the PAB at 10:00 and completed the
parameters of the RT task (e.g., task length, ISI, etc), response tasksinafixedorderasfollows:
conditions, and visual analogue scales. Data was downloaded each
weekinthelaboratory.Participantsweretrainedonhowtousethe ProfileofMoodStates(POMS):Participantswereaskedtoratetheir
reactiontimedevice,andthenpracticedeachtaskintheperformance moodona5-pointscalefor30adjectives[46].Analysiswasdone
assessment battery (PAB) that would be administered in laboratory on a total mood score as well as six identifiable subscales
sessionswiththe2-backmemorytestbeingcompletedtwice.Practice including:Vigor–Activity(V),Fatigue–Inertia(F),Tension–Anxiety
data was checked for accuracy in order to ensure participants (T), Confusion–Bewilderment (C), Depression–Dejection (D),
understood task instructions. The importance of strict compliance Anger–Hostility(A),and.ThePOMSwasadministeredonpaper.
withinstructionsandthetimingofallaspectsoftheprotocolwere
Pitch ERP oddball task: Participants were asked to discriminate
impartedtoparticipantsatthistime.
betweentwotonesdifferinginpitchandrespondtothehigher-
pitched‘target’tone(ISI=1–2satrandom;taskduration=6min).
1.2.2.Homeassessment
Thestandardtone(1000Hz,100ms,70dB)waspresentedon80%
Participants were instructed to wear an activity monitor on the
wrist,whichresembledawatch,foreachofthe21daysandnights. oftrialsandthetargettone(1500Hz,100ms,70dB)waspresented
Theyweretoldonlytoremovethemonitorsothatitdidnotgetwet ontheremaining20%oftrials.
(e.g.,whenshowering)ordamaged(e.g.,whenplayingcontactsports). VisualRTtask:Awarningtoneprecededthepresentationofacircle
Theactivitymonitorswerepresettobeginrecordingat18:00onthe onthescreen.Theparticipantwasaskedtorespondasquicklyas
dayoftraining.Participantswerealsoaskedtokeepasleep-activity possibletothevisualstimulus.Whileinitiallydesignedtopilottest
diary,indicatingtheirtimeinbedandsleeptime,aswellasanymeals, a CNV task, it was used only as a filler task between auditory
snacks, caffeine intake, alcohol consumption, and exercise. Partici-
oddballtasksandwasnotanalyzedfurther.
pantswereinstructedtobeginthisdiaryat18:00onthedayoftheir
DurationERPoddballtask:Participantswereaskedtodiscriminate
training. They were also given a hand-held RT monitor; they were
between tones of two different durations, and respond to the
instructedtoself-administera10-minuteRTtask,5timesoneachof
shorter duration ‘target’ tone (ISI=1–2 s at random; task
the21days(i.e.,09:00,12:00,15:00,18:00,21:00).Theyweretobegin
duration=6min).Thestandardtone(250Hz,200ms,70dB)was
thistaskat09:00thefollowingmorning(i.e.,Day1oftheprotocol).
Thehand-heldRTmonitoralsodeliveredvisualanaloguescales(VAS) presented on 80% of trials and the target tone (250 Hz,100 ms,
ofsleepinessandmoodpriortotheRTtask,wherehighervaluesona 70dB)waspresentedontheremaining20%oftrials.
16-pointscalereflectedmorealertnessandhappinessrespectively.On Break:10-min.
their study instruction log, participants were required to sign their Reactiontimetask:Participantswereaskedtorespondtoa70dB
initials and log the time that each RT task was completed. The RT toneasquicklyaspossibleusingthe“zero”keyonthekeypadfor
monitoralsologgedtheexacttimethetaskwascompletedsothatthe 10min.Theinter-stimulusintervalvariedfrom2–10s.
accuracyofparticipants'logscouldbeverified. 2-back memory task: Participants identified cases in which the
Forthesecondweek,eachparticipant'ssleepwasrestrictedby33%
letter that appeared on the computer screen matched the letter
oftheirbaseline.Inordertocalculatethissleeprestriction,anaverage
that had appeared two before it, and responded to the second
timeinbed(lessmajorwaketime)wascalculatedasanestimateof
letter of the matching pair (Stimulus duration=250 ms,
habitualsleeptime.Sleepwasrestrictedbothbydelayingbedtimeand
byadvancingrisetime(i.e.,16.5%oftotaltimeinbedwastruncated ISI=1750 ms). Three consecutive blocks were administered with
fromboththebeginningandendofthenight).Specificlights-outand a30sbreakinbetweenblocks.Eachblockcontained18targetsand
lights-ontimeswerecommunicatedtotheparticipant.Actigraphyand 42standardtrialspresentedinapseudo-randomfashion.
diary data confirmed that participants complied with these Alphaattenuationtask:Duringthis3-mintask,participantssatstill
instructions. withtheireyesalternatelyopenedorclosed,for30satatime.EEG
was recorded from 19-sites during the task. Participants were
1.2.3.Laboratoryassessment instructedtoremainstillwitheyesfixatedonan‘X’appearingon
Participants visited the laboratory from 09:00 until 11:00 a.m.
thecomputerscreen.Thistaskprovidedaquantitativemeasureof
according to the following schedule: on the morning of Day 7
physiologicalsleepinessandarousal[47].
(following 7th night of baseline), Day 8 (following 1st night of
StanfordSleepinessScale:Participantsuseda7-pointscaletorate
restrictedsleep),Day11(following4thnightofrestrictedsleep),Day
their level of alertness or sleepiness, where ‘7’ indicated the
14(following7thnightofrestrictedsleep),andDay15(following1st
nightofrecovery).Oneachoccasion,theparticipants'actigraphrecord greatestamountofsleepiness[48].
and sleep-activity diary were examined to ensure that they had Subjective Performance Scale: Participants rated their subjective
compliedwithinstructionsrelatedtosleep/waketimes,napping,and performanceona5-pointscale(1=verypoor,5=verygood).
caffeineconsumption.Thedatafromtheparticipants'reactiontime
devicewerealsoexaminedtoensurethatalltestshadbeencompleted 1.3.Dataanalysis
attheappropriatetimes.
Electrophysiologicalsignalswererecordedat200HzwithLamont Thescreeningnightwassleepscoredaccordingtostandardcriteria
digital amplifiers (analogfilters preset at .05–70Hz), and displayed [49] and checked for the presence of sleep-related breathing and
and analyzed using Harmonie software (Stellate, Inc). Using an movementdisorders.Actigraphy,RTanddiarydatawerecheckedfor
electrode cap, a 19-channel montage was recorded from frontal– compliance and downloaded to computer upon each visit to the
parietal (FP1, FP2), frontal (F3, Fz, F4, F7, F8), central (C3, Cz, C4), laboratory.Anumberofcompositevariableswerecalculatedfromthe
temporal(T7,T8),parietal(P3,Pz,P4,P7,P8),andoccipital(O1,O2) raw RT data collected at home and in-laboratory sessions. These
scalpsites.ReferenceswereplacedatA1andA2andgroundatAFz. variablesincludedmeanRT,10%fastestRTs,10%slowestRTs,andthe
VerticalandhorizontalEOGchannelswererecorded,aswellasEMG, numberoflapses(RTsN500ms).Alapseisamissedorslowresponse
to allow for offline artifact rejection. Waking EEG and ERPs were thatisduetoa“lapse”inattention.
K.A.Coteetal./Physiology&Behavior95(2008)353–364 357
Waking EEG datafromtheAlpha AttenuationTaskwasquantified 2.1.Actigraphyanddiaries
using Fast Fourier Transform (FFT) analysis techniques. Artifact-free
epochsweresubmittedtopowerspectralanalysis(PSA)usingahanning To validate compliance with instructions to curtail sleep, diary
window method (75% overlap; spectral record length=5.12 s; FFT estimatesoftotalsleeptimeandthelevelofinactivityfromactivity
length=2.56 s). Data were re-referenced offline to an average of A1 monitorswerecomparedbetweenbaseline,restriction,andrecovery
andA2priortospectralanalysis.EEGdatawerequantifiedasthepower weeks using one-way ANOVAs. Participants reported sleeping
(µV2/Hz)ofeachofthefollowingpre-definedfrequencybands:theta,4– significantly less during the CSR week compared to baseline
8Hz;lowfrequencyalpha,8–10Hz;highfrequencyalpha,10–12Hz. (pb.001) and recovery weeks (pb.001), F(2,22)=79.79, pb.001,
AbsolutepowerineachbandwasexaminedtocharacterizeCNSarousal eta2=.88.Dataweremissingfromtwoparticipantsduetoambiguous
throughoutsleeprestriction.Inaddition,theratioofalphatothetapower diary entries at some point during the 21-day protocol. Activity
(lower values represent reduced arousal) and the Alpha Attenuation monitors showed that there was significantly less “inactivity” (i.e.,
Coefficient(ratioofeyesclosedtoeyesopenalpha;lowervaluesreflect sleep)duringtheCSRweekcomparedtotherecoveryweek(pb.001),
reducedarousal)werecalculated.EEGdatawerelogtransformedpriorto andatrendforlessactivityduringtheCSRweekcomparedtobaseline
statisticalanalysisduetotheskewednatureofthedata. (p=.061),F(2,22)=6.63,pb.01,eta2=.38.Dataweremissingfromtwo
ERPs were obtained from electrophysiological data recorded participantsbecauseofpartialmissingdatafromtheactivitymonitor
during both the pitch and duration auditory oddball tasks, and due to technical problems. See Table 1 for means and standard
analyzed using ERPScore [50]. Target and non-target trials were deviationsofthehomedata.
averaged separately. A software-driven automatic artifact rejection
routinewasusedtoidentifyandremoveanytrialsonwhichtheEEG 2.2.Homedata
or EOG exceeded +/−100 µV in order to remove artifact from eye
movements. A grand average ERP was determined for each study Datacollectedevery3-hwhileathome(i.e.,RT,mood,sleepiness)
condition. After artifact rejection, the average number of trials in wascollapsedacrosstime-of-dayforadailyaveragevalue.Thedaily
grand averages for each PAB session was 194 targets and 807 average accurately reflected data from each time-of-day, except for
standards for the pitch oddball and 195 targets and 733 standards moodandsleepinessvariablesforwhichthemorningdata(at09:00)
for the duration oddball task. Based on the peaks apparent in the were relatively lower (presumably due to sleep inertia). Therefore,
grandaverages,N1andP2amplitudeandlatencywerethenmeasured ANOVAswererunforsleepinessandmoodwith09:00dataexcluded
following standard stimuli in the within-subject averages. The from the daily average. Subjective sleepiness differed significantly
amplitude and latency of N1 was measured as the most negative across study condition, F(1.36,17.71)=8.10, pb.01, eta2=.38. Specifi-
peak between 80 and 150 ms and P2 was the most positive peak cally, sleepiness was lower on baseline compared to both the CSR
between 150 and 250 ms. To measure the long-latency P300, the (pb.01) and recovery weeks (pb.05). Although sleepiness did not
averageamplitudevaluewasmeasuredinthewithin-subjectaverages returntobaselinelevels,significantquadraticpolynomialsprovided
from the latency range where the peak was apparent in the grand evidenceofsomeimprovementduringrecovery,F(1,13)=7.88,pb.05,
averageforthepitch(300–450ms)andtheduration(400–650ms) eta2=.38. Subjective mood reports did not differ significantly by
targetstimuliseparately.N1andP2appearassharppeakswhichare condition,however,therewasalineardeclineinmood,F(1,13)=5.10,
easily identifiable in the individual averages and thus precise pb.05, eta2=.28, which showed that mood deteriorated from the
measurementofthepeakamplitudeispossible;however,theP300 baselinetotheCSRweek,andremainedlowduringrecovery.
peakisarelativelyslowwavelastingabout200ms,soitsamplitudeis One-wayANOVAswereruntocompareRTacrossthethreestudy
more accurately measured by taking the average amplitude values weeks. There was a significant condition effect for mean RT, F(1.27,
acrossawiderrange. 16.51)=5.06, pb.05, eta2=.28. Mean RT during baseline was faster
Validationdata(sleeptimeandactivitylevel)andbehaviouraldata comparedtotherecoveryweek(pb.05),withatrendforbaselinealso
from home (RT, mood, sleepiness) were analyzed using one-way beingfasterthantheCSRweek(p=.054).Thefastest10%RTsdidnot
repeated measures ANOVAs (baseline, restriction, recovery weeks). reachsignificanceforthemaineffect,however,therewasatrendfora
Significant F-tests were followed up with planned Least Significant quadratic effect, F(1,13)=3.65, p=.078, illustrating the predicted
Differences(LSD)comparisons.Allbehaviouralandphysiologicaldata directionofchangeinperformancefrombaselinetosleeprestriction
collected in the laboratory were analyzed using one-way repeated and to recovery. The slowest 10% RTs significantly differed across
measures ANOVAs (baseline, 1st day of restriction, 4th day of condition,F(2,26)=21.56,pb.001,eta2=.62.RTwasslowerduringCSR
restriction, 7th day of restriction, recovery), and followed up with (pb.001)and recovery(pb.001)comparedtobaseline.Asignificant
LSDplannedcomparisons.Giventhedesignofthestudy,significant quadratic effect indicated there was a slight return to baseline in
quadratic polynomials were also predicted to show deficits in recovery,F(1,13)=6.48,pb.05,eta2=.68.Therewasalsoasignificant
performance from baseline to restriction, followed by a return to condition effect for the number of RT lapses, F(1.19, 15.40)=12.02,
baselinelevelsduringrecovery.Inaddition,linearchangesacrossthe
sleeprestrictionweekwereexpected.Boxplotswereusedtoidentify
Table1
outliers on all variables; outliers more than 3 standard deviations Averagedweeklyvaluesforhomedataduringbaseline,sleeprestriction,andrecovery
beyondthemeanatbaselinewereremovedfromanalysis.Violations weeks
to assumptions of sphericity were corrected using Greenhouse–
Baselineweek Sleeprestriction Recoveryweek
Geissercorrectionsasnotedin theadjusted degreesoffreedom for week
eachanalysisifappropriate.Missingdataareindicatedintheresults Variable Mean SD Mean SD Mean SD
sectionforeachvariable.
Estimatedsleeptime(hours) 8.29 .80 5.38 .50 7.79 .42
Inactivityfromactigraph 446.83 93.10 379.05 38.49 489.27 66.05
2.Results SleepinessVAS 10.05 1.35 8.69 1.64 9.43 1.18
MoodVAS 10.01 1.59 9.67 1.62 9.57 1.51
MeanRT 326.41 88.41 437.08 225.50 447.64 197.47
Examination of polysomnographic data on the screening night
Slowest10%RTs 623.89 241.49 1081.40 874.4 1204.09 968.84
confirmed that all participants were good sleepers. Specifically, Fastest10%RTs 187.87 26.01 197.93 34.65 194.09 41.02
participants slept an average of 6.8 h (M=408.07 min; SD=46.02), No.oflapses 5.08 4.71 11.41 11.19 14.52 13.19
fell asleepin an averageof 9.39 min (SD=8.03),and had anoverall
Note: Higher number on VAS scales represent more alertness and happiness
sleepefficiencyof91percent(SD=6.53). respectively.MeanRT,10%fastestand10%slowestRTsarepresentedinmilliseconds.
358 K.A.Coteetal./Physiology&Behavior95(2008)353–364
pb.005, eta2=.48, with each subsequent study condition showing (pb.01).Similarly,Vigorwashigheronthe1stdayofsleeprestriction
significantlymorelapses(psb.01). compared to the 4th (pb.005) and 7th (pb.01) days of sleep
restriction and recovery (pb.05). However, a significant
2.3.Laboratorydata quadraticeffectreflectedthereturntowardbaselineduringrecovery,
F(1,12)=30.19,pb.001,eta2=.72.Therewasalsoasignificantmain
2.3.1.Behaviouraldata effectfortheF-subscale,F(4,48)=5.34,pb.001,eta2=.31.Fatiguewas
See Table 2 for means and standard deviations. Subjective significantlyloweronbaselinecomparedtothe4th(pb.001)and7th
sleepiness, perception of performance, mood, and RT changed as (pb.05)daysofsleeprestriction,andalsosignificantlylowerafterthe
predicted during sleep restriction relative to baseline and recovery 1stdayofsleeprestrictioncomparedtothe4th(pb.001)and7th
conditions. Significant condition effects and quadratic polynomials (pb.05)daysofsleeprestriction.Therewasasignificantquadratic
depictedthefollowingchangesduringCSR: effect, F(1,12)=11.25, pb.01, due to a peak in Fatigue during the
middleofthesleeprestrictionweek.TherewasonlyatrendfortheC-
Subjectivesleepiness.Oneparticipantwasexcludedfromthisanalysis subscaleofmood,F(2.56,30.69)=2.95,p=.056;meansshowedthat
duetomissingdata.Therewasasignificantmaineffect,F(4,48)=5.84, Confusionwasgreateronthe4thdayofsleeprestrictioncomparedto
pb.001,eta2=.33,andquadraticpolynomial,F(1,12)=23.27,pb.001, the 1st day of sleep restriction. The Tension–Anxiety (T), Anger–
eta2=.66.Participantsweresleepieronthe4th(pb.001)and7thdays Hostility(A),andDepression–Dejection(D)subscalesdidnotyield
of restriction (pb.01) compared to baseline, sleepier on the 4th significance.
comparedtothe1stdayofrestriction(pb.05),andsleepieronthe4th Reactiontime.MeanRT,medianRT,standarddeviationofRTs,slowest
(pb.005)and7thdaysofrestriction(pb.05)comparedtorecovery. 10%RTs,fastest10%RTs,andRTlapseswereallcalculatedfromtheRT
Perceptionofperformance.Oneparticipanthadmissingdata.There taskadministeredinthelaboratory.Threeparticipantshadmissing
wasasignificantmaineffect,F(4,48)=4.46,pb.005,eta2=.27,and datafromatleastoneofthestudyconditions.Therewasasignificant
quadraticpolynomialF(1,12)=18.45,pb.001,eta2=.61.Participants main effect, F(1.86,18.64)=3.86, pb.05, eta2=.28, and quadratic
reportedthattheywereperformingbetteronbaselinecompared polynomial,F(1,10)=11.21,pb.01,eta2=.53,formeanRT.Participants
tothe4thdayofsleeprestriction(pb.01),andbetteronrecovery were faster atbaseline compared to the 4th(pb.01) day of sleep
compared to the 4th (pb.005) and 7th days (pb.005) of sleep restriction[includingatrendtoalsobefasteratbaselinethanthe7th
restriction. There were also trends for the perception of better dayofrestriction,p=.051],andfasterfollowingrecoverycompared
performance on baseline compared to the 7th day of restriction tothe4th(pb.001)and7th(pb.05)daysofsleeprestriction.There
(p=.068),andforbetterperformanceonrecoverycomparedtothe wasalsoatrendforslowedRTperformancefromthe1sttothe4th
1stdayofsleeprestriction(p=.053). daysofsleeprestriction(p=.089).TheresultsformedianRTwere
POMS mood. The total mood score, and the Vigor–Activity (V), similar, F(1.58, 15.85)=3.99, pb.05, eta2=.29: participants were
Fatigue–Inertia (F), and Confusion–Bewilderment (C) subscales of significantlyfasteratbaselinecomparedtothe4th(pb.05)and7th
thePOMSshowedtheexpectedeffectsofsleeprestriction.Therewas (pb.05)daysofsleeprestriction,andfasteratrecoverycomparedto
one missing participant from this analysis due to incomplete the 4th (pb.005) and 7th (pb.05) days of sleep restriction. There
data entry on the paper form. For total mood, there was a main weretrendsindicatingthatfollowingthe1stdayofsleeprestriction,
effect,F(4,48)=6.60,pb.001,eta2=.36.Moodwassignificantlybetter RTwasfasterstillcomparedtothe4th(p=.056)and7th(p=.070)
onbaselinethanonthe4th(pb.001)and7th(pb.05)daysofsleep daysofsleeprestriction.Thefastestandslowest10%RTs,aswellas
restriction. Mood on the 1st day of sleep restriction was also the number of RT lapses showed trend level main effects but
significantlybetterthanthe4th(pb.001)and7th(pb.05)daysof significantquadraticeffectsaspredicted.Specifically,thefastest10%
sleeprestriction,aswellasrecovery(pb.05).Asignificantquadratic RTsshowedatrendforthemaineffect,F(4,40)=2.40,p=.066,buta
effect, F(1,12)=11.83, pb.005, eta2=.50, showed that mood was significant quadratic effect, F(1,10)=5.93, pb.05, eta2=.37; RT was
returningtowardbaselineduringrecovery.FortheV-subscale,there fasteratbaseline(pb.05)andrecovery(pb.01)comparedtothe4th
was a main effect for condition, F(2.17, 26.01)=9.59, pb.001, dayofrestriction.Theslowest10%RTsshowedatrendforthemain
eta2=.44; Vigor was higher on baseline compared to the 4th effect,F(2.13,21.26)=3.24,p=.057,butarobustquadraticeffect,
(pb.001) and 7th (pb.005) days of sleep restriction and recovery F(1,10)=12.64,pb.01,eta2=.56;RTwasslowerfollowingthe4th
Table2
Laboratoryassessmentofsubjectiveandbehaviouralperformancevariables
Variable Baseline Sleeprestriction Sleeprestriction Sleeprestriction Recovery
(Day1) (Day4) (Day7)
Mean SD Mean SD Mean SD Mean SD Mean SD
Subjectivevariables Subjectivesleepiness 3.92 1.26 4.31 1.18 5.31 1.03 4.92 1.32 3.92 1.50
Perceptionofperformance 3.23 .73 3.00 1.00 2.62 .77 2.69 .95 3.46 .88
POMSmood Totalmoodscore 13.69 12.20 14.92 11.91 25.54 11.13 24.92 15.31 21.62 17.84
V-scale 6.08 3.97 4.77 2.52 2.62 2.66 2.62 3.36 3.31 3.01
F-scale 6.62 3.88 6.85 4.08 11.69 2.50 10.85 4.88 9.62 6.63
T-scale 2.62 3.75 2.31 2.59 2.85 3.46 2.62 3.73 2.46 3.46
C-scale 5.15 2.64 4.69 2.25 6.31 3.17 6.85 2.82 6.38 3.07
D-scale 3.08 4.50 2.85 4.16 3.08 3.35 2.92 3.82 2.62 3.32
A-scale 3.08 2.81 3.00 3.06 4.23 3.22 4.01 3.79 3.85 4.12
RT MeanRT 337.52 70.28 348.83 66.47 377.92 84.34 392.48 99.97 350.05 78.46
MedianRT 320.86 69.15 327.09 65.46 356.68 86.59 385.68 110.00 335.45 78.93
SDRT 83.06 20.16 94.06 28.36 105.14 44.85 108.38 65.82 84.03 30.47
Slowest10%RTs 499.81 99.21 532.29 134.60 586.00 148.58 583.68 175.62 502.91 121.60
Fastest10%RTs 256.33 58.04 263.71 60.45 276.18 66.37 279.64 57.00 262.60 67.91
No.oflapses 5.55 6.11 7.27 8.39 15.36 19.57 17.91 23.95 8.91 14.05
n-backmemory MeanRT 464.21 58.38 477.70 70.38 483.41 49.24 474.72 73.39 444.27 49.24
%Accuracy 91.36 11.09 93.67 6.43 89.51 10.78 87.04 13.90 92.28 8.71
POMSsubscales:Vigor–Activity(V),Fatigue–Inertia(F),Tension–Anxiety(T),Confusion–Bewilderment(C),Depression–Dejection(D),Anger–Hostility(A).
K
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Fig.2.DynamictopographyofalphaEEGduringsleeprestriction.Atfrontalsites,alineardeclineinEEGarousalisseenovertheweek.Atposteriorsites,changesoccuronlyattheendofsleeprestrictionweek.Note:valuesrepresentthemean
logpower(withstandarderrorindicated). 3
5
9
360 K.A.Coteetal./Physiology&Behavior95(2008)353–364
dayof sleep restriction compared to both baseline (pb.05) and restriction;atbothP7andO2,arousalwashigheratbaselinethanall
recovery (pb.01); RT at recovery was also faster than the 7th otherconditions,andhigherafterthe1stnightcomparedtothe7th
(pb.01)dayofsleeprestriction.Similarly,therewasatrendfor nightofrestriction;atP8,arousalwashigheratbothbaselineandafter
the main effect of lapses, F(1.59, 15.89)=3.57, p=.061, with a the 1st night of sleep restriction compared to the 7th night of
significant quadratic effect, F(1,10)=7.16, pb.05,eta2=.42; there restriction;andatO1,arousalwashigheratbaselinethanthe4thand
wereagreaternumberoflapsesinresponsetimefollowingthe 7thnightofrestrictionand recovery,andhigherafterthe1st night
4th day of sleep restriction compared to both baseline (pb.05) restrictioncomparedtothe7thnightofrestrictionandrecovery.Atall
and recovery (pb.01); there was also a trend for more lapses of these posterior sites, there was a significant linear polynomial
followingthe7thdayofsleeprestrictioncomparedtorecovery which depicted the decline in alertness over conditions (psb.05).
(p=.050).ThestandarddeviationofRTsdidnotyieldsignificant Inspectionofthemeansplotsshowedthatarousalwasincreasingat
differences. recovery at all of the posterior sites above, however, significant
2-backmemorytask.MeanRT,thestandarddeviationofRTs,and quadraticpolynomialsprovidedsupportforthisrecoveryatonlyP4
percentaccuracyonthe2-backmemorytaskwereassessed.One (p=.05)andO2(pb.05)sites.
participantwasremovedbecauseaccuracydataindicatedafailure The alpha attenuation coefficient (AAC) was examined using a
tounderstandthetask,andtwootherswereexcludedbecauseof one-way ANOVA to compare across the five laboratory testing
missing data in at least one condition. There was a trend for a sessions(baseline,1st,4th,7th nights of restriction, andrecovery).
conditioneffectformeanRT,F(4,40)=2.24,p=.08,andaquadratic Only the AAC calculated with low frequency alpha yielded signifi-
effect,F(1,10)=12.04,pb.01,eta2=.55,whichdepictedtheexpected cance.Resultsshowedgreaterphysiologicalsleepinessfollowingthe
effectsofsleeprestriction(seeTable2formeans).MeanRTwas 7th night of sleep restriction compared to baseline, 1st night of
fasterfollowingonenightofrecoverysleepcomparedtothe4th restriction, 4th nightof restriction, and recoveryat Fz , Cz, and C4
(pb.001)dayofrestriction,withsimilartrendscomparedtothe1st (psb.05),andatrendforthesameoutcomeatPz.Inaddition,atFz,
(p=.06) and 7th (p=.09). The standard deviation of RTs and therewasgreaterphysiologicalsleepinessfollowingthe4thnightof
accuracyvariablesdidnotyieldsignificantdifferences. restriction (pb.05) compared to baseline. No other sites were
Physiological data. EEG. Absolute power in pre-defined EEG significant.TofurtherinvestigatethescalptopographyofEEGslowing
frequency bands (theta, low frequency alpha, high frequency duringthesleeprestriction,follow-upone-wayANOVAswererunto
alpha) was examined during eyes opened and closed recording compare the AAC across the week of sleep restriction. Changes in
sessions. No outliers were identified in EEG power. Only low physiological alertness emerged as follows (refer to Fig. 2 for
frequencyalpha(8–10Hz)duringeyesclosedrecordingsessions illustrationoftopography):the1stdaydifferedfromthe7thdayof
varied across study condition: alpha was higher at baseline restriction at right-hemisphere anterior sites (Fp2, Fz, F8, T8), and
(psb.05) compared to all other conditions at posterior sites (P3, significantlinearpolynomialsalsodepictedthiscontinuousdeclinein
Pz, P4, P7, P8, O1, O2), and higher after the 1st night of sleep arousal;the4thdaydifferedfromthe7thdayofrestrictionatright-
restriction(psb.05)comparedtothe7thnightofsleeprestriction hemisphereposteriorsites(P4,Pz,withtrendsatP7/P8);andboththe
foralloftheaboveposteriorsites,exceptP4.Significantquadratic lineardeclinefromthe1sttothe7thnightofsleeprestrictionaswell
polynomialsatalloftheposteriorsitesshowedthatalphalevels asthesharpdeclinefromthe4thtothe7thnightofsleeprestriction
wereincreasingafteronenightofrecovery. were seen at right-hemisphere central sites (Cz, C4). There were
trendsforsimilareffectsatleft-hemispheresites(seeTable3),which
The alpha to theta ratio variable (using low frequency alpha) shows that although the decrease in physiological alertness was
differedsignificantlyacrossconditionatposteriorsites(P3,P4,P7,P8, widespreadacrossthescalp,theeffectsintheright-hemispherewere
O1, O2).The differenceswereas follows (all psb.05):at P3, arousal morerobust.
wasloweron7thdayofrestrictioncomparedtobaselineandthe1st
and 4th days of restriction, and arousal was lower on recovery Event-related potentials. Behavioural performance on the pitch
compared to baseline; at P4, the outcome was the same as for P3 anddurationoddballtaskswaslargelyuninfluencedbysleepre-
exceptthatarousalwasalsohigheratbaselinethanthe1stnightof striction. Percent accuracy to both target stimuli (i.e., providing
Table3
Resultsof3-wayANOVAsontheAlphaAttenuationCoefficient(AAC)
Region Site n Conditionmaineffect Linearpolynomialcontrast LSDpairwisecomparisons
F-statistic p-value Effectsize F-statistic p-value Effectsize
Frontal Fp1 12 2.650 .093 .194 3.771 .078 .255 SR1≠SR7(p=.078)
Fp2 12 3.760 .039 .255 5.951 .033 .351 SR1≠SR7(p=.033)
F3 11 3.333 .056 .250 4.966 .050 .332 SR1≠SR7(p=.050)
Fz 11 5.639 .011 .361 9.215 .013 .480 SR1≠SR7(p=.013);SR4≠SR7(p=.050)
F4 12 2.968 .072 .212 4.294 .063 .281 SR1≠SR7(p=.063)
F7 11 2.826 .083 .220 3.206 .104 – SR1≠SR4(p=.088);
F8 12 3.728 .040 .253 5.494 .039 .333 SR1≠SR7(p=.039)
Central C3 12 1.720 .202 – 3.122 .105 –
Cz 10 5.562 .013 .382 8.670 .016 .491 SR1≠SR7(p=.016);SR4≠SR7(p=.021)
C4 11 4.918 .018 .330 8.293 .016 .453 SR1≠SR7(p=.016);SR4≠SR7(p=.015)
Temporal T7 11 1.979 .164 – 2.313 .159 –
T8 12 5.365 .013 .328 9.108 .012 .453 SR1≠SR7(p=.021);SR1≠SR4(p=.087)
Parietal P3 12 2.492 .106 – 2.603 .135 –
Pz 11 3.340 .083 .250 3.279 .100 – SR4≠SR7(p=.032)
P4 12 4.248 .028 .279 4.520 .057 .291 SR4≠SR7(p=.037);SR1≠SR7(p=.057);
P7 12 3.589 .045 .246 4.766 .052 .302 SR1≠SR7(p=.052);SR4≠SR7(p=.067)
P8 12 3.469 .049 .240 3.908 .074 .262 SR1≠SR7(p=.044);SR4≠SR7(p=.074);
Occipital O1 12 2.163 .162 – 2.479 .144 –
O2 12 3.127 .090 .221 3.607 .084 .247 SR1≠SR7(p=.084)
Note:SR1,SR4,andSR7representthe1st,4th,and7thnightsofsleeprestriction.PairwisecomparisonsarereportedfortrendstoshowtopographicpatternofEEGchanges.
Significancewherepb.05appearsinbold.
K.A.Coteetal./Physiology&Behavior95(2008)353–364 361
response)andstandardstimuli(i.e.,inhibitingresponse)didnot amplitudeandlatencyweremeasuredfollowingstandardstimuli.
vary significantly by condition. Similarly, the one-way ANOVAs For both oddball paradigms, the predicted effects of sleep
comparingacrossbaseline,1st,4th,7thnightsofrestriction,and restrictionwerenotapparentatanysiteforN1andP2latencyor
recovery,didnotyieldsignificanceformeanRTtotargetstimulifor amplitude.Forthepitchoddballtask,thereweresignificantcon-
either the pitch or duration oddball tasks. However, closer ditioneffectsandalinearincreaseinP2amplitudeoverthefive
examination of the sleep restriction week alone showed that studyconditionsthat wereapparentatallfrontal sites(psb.05).
meanRTtopitchtargetswassignificantlyslowerfollowingthe7th ThereweresimilareffectsfoundforP2amplitudefortheduration
nightcomparedto4thnightofrestriction(pb.05),F(2,20)=3.66, task,however,theeffectswerenotasstatisticallyrobust.
pb.05, eta2=.27. There was a trend for mean RT to duration The average amplitude of the long-latency P300 was measured
targets,F(2,20)=3.11,p=.067,drivenbyRTsbeingslowerfollowing from300–450msforthepitchstimuliandfrom400–650msfor
7thnightcomparedto4thnightofrestriction(pb.01).N1andP2 thedurationstimuli.Forbothanalyses,oneoutlierwasremoved
Fig.3.A.MeansplotofP300amplitudeatPzfollowingpitchtargets.NotethattheP300waveformbecomessmaller(i.e.,lesspositive)duringsleeprestriction,andreturnstobaseline
followingrecovery.B.ERPstopitchtargetsatparietalsites.P300isnotedasalargeupwarddeflectionoccurringfrom200–500ms.Baseline=thinsolid,SR1=thin,dashed,SR4=thin,
brokenline,SR7=thicksolid,andRecovery=thick,dashedline.
362 K.A.Coteetal./Physiology&Behavior95(2008)353–364
because of extreme values at parietal sites during baseline (i.e., thatfrontallobeimpairmentisresponsibleforthebehaviouraldeficits
negativeamplitude).Forthepitchoddballtask,one-wayANOVAs seen during sleep loss [7]. Furthermore, the localization of arousal
wererunateachsitetocompareP300amplitudeacrossthefive changes to frontal regions is consistent with EEG studies following
studyconditions.Therewasatrendfortheexpectedreductionin totalsleepdeprivation[17,26,27],andconsistentwithsomeimaging
P300 amplitude at Pz, F(4,28)=2.59, p=.058, with a significant datashowingreducedactivityinfrontalbrainregionsfollowingtotal
quadratic effect, F(1,7)=6.40, pb.05, eta2=.48. P300 was smaller sleepdeprivation[8–11].Atleastinitially,CNSfunctionintheparietal
(lesspositive)onthe7thdayofsleeprestrictioncomparedtoboth regionsseemedtobemaintained,providingevidencefortheoriesof
1stdayofsleeprestriction(pb.05)andrecovery(pb.05),witha braincompensationthathavebeenproposed[15].Theparietalbrain
trendforalsobeingsmallerthanbaseline(p=.069).SeeFig.3for regionsmaysimplybeabletofunctionlongerduringthechallengeor
themeansplotsofP300amplitudechangesacrossconditionatPz stress of sleep deprivation. As the duration of sleep restriction
andthegrandaverageERPwaveformsatparietalsites.Therewas continued, deficits also became apparent in parietal brain regions.
alsoasignificantquadraticeffectfortheright-hemisphereparietal Presumably,eithercompensationfailsatthispoint,ortheextentof
site,P4,F(1,7)=7.69,pb.05,eta2=.52,althoughtheconditioneffect brainregionscompromisedbysleeprestrictionbecomesmorewide-
wasnotsignificant.Therewerenosignificanteffectsortrendsat spread.Thesedatasuggestthatthelengthordurationofcontinuous
the left-parietal lead, P3, nor at any other sites recorded. P300 sleeprestrictionmaybeamoreimportantindicatorofthemagnitude
amplitude to the target stimuli did not vary reliably across ofdeficitsthanthedegreeofsleeploss.Inotherwords,thebrainmay
conditionforthedurationoddballtask. becapableofadaptationorcompensationforshortperiodsevenwhen
thesleeplossisextreme(e.g.,24h);however,thebrainmaynotbe
3.Discussion adaptablewhenthereisachroniclackofsufficientsleep.
ERPstothetargetstimuliinthepitchoddballtaskrevealedreduced
Datafromweeklyaveragesofsleepdiariesandactigraphmonitors P300amplitudeatparietalsitesduringsleeprestriction.Thesefindings
showed that participants complied with the instruction to curtail are consistent with previous studies that found reductions in P300
sleepathome.Behaviouraldatacollectedfromhomeshowedsome amplitudefollowingtotalsleepdeprivation[31–34,36,37].Thus,sleep
effects of sleep restriction with subjective sleepiness and mean RT restriction, a more subtle degree of sleep loss that is commonly
being reduced during the week of sleep restriction compared to experienced,ledtoimpairmentintheabilitytoallocateattentionto
baseline.Therewasnoevidenceofimprovementduringtherecovery targetdiscriminationorpossiblydeficitsinmemoryupdating[35,51].
weekfordatacollectedfromhome,andmoreovertherewerelinear Earliercomponents,N1andP2,weremeasuredfromthefrequently
declinesoverthestudyperiodseeninmoodandRTlapsessuggesting occurringstandardstimuli.ItwasexpectedthatN1wouldbesmaller
problemswithparticipants'motivationwhendatawerecollectedat and P2 would be larger in amplitude during sleep restriction
home. Measurement taken during the laboratory sessions revealed representingreducedattentiontowardthelessmeaningfulnon-target
more robust effects in the expected direction for sleepiness, mood, stimuli[52].Therewerenoeffectsofsleeprestrictionfortheamplitude
and RT. These behavioural findings were consistent with previous orlatencyofthesecomponentsthatindexearlystagesofinformation
studies of continuous sleep restriction [39,41,42], further validating processing (e.g., stimulusidentification and encoding).However, P2
thatsleepwassuccessfullymanipulatedathome.Electrophysiological amplitude increased linearly over all study conditions (baseline,
measuresofEEGandERPsshoweddynamicchangesinarousaland restriction,andrecovery).ItispossiblethatthelinearincreaseinP2
attention as a result of sleep restriction. Specifically, EEG data amplitudeoverthestudyprotocolreflectsreducedmotivationoreffort
indicated that anterior brain regions showed immediate and con- onthemundanetaskoverrepeatedmeasures.Leeetal.notedasimilar
tinuousreductionsinarousal,whereasposteriorregionsdidnotshow increaseinP2amplitudeover2daysoftotalsleepdeprivationwhich
changes until later in the sleep restriction week. Impairment in they related to mood and anxiety [33]. Given the linear changes in
attentionalsoemergedtowardtheendofthesleeprestrictionperiod, mood reported here, it may be that the systematic increase in P2
as seen in the P300 component of the ERP which was reduced in amplitudeovertimecanbeexplainedbyemotiondysregulationasa
amplitudeatparietalsiteswherethecomponentistypicallylargest. resultofboththesleeplossandthelengthyparadigmcombined.ERPs
BothEEGandERPdatarevealedthattheeffectsofsleeprestriction inthedurationoddballtaskdidnotvarywithsleeprestriction.This
were more robust in the right-hemisphere, perhaps demonstrating outcomewassurprisingbecauseweexpectedthatthisrelativelymore
greaterresiliencyofthedominanthemisphere.Insummary,anumber difficultstimulusdiscriminationtaskwouldbemoresensitivetothe
of different variables converge to show that there are deficits in effectsofsleeploss.Indeedthereisevidencethatthedurationtaskwas
performance and brain function which are apparent after four and moredifficult:accuracywasgreater,RTwasfaster,andP300amplitude
sevennightsofcontinuoussleeprestriction. washigheratbaselineforthepitchtargets(90.72%,376.82ms,8.80µV)
One of the main goals of the present study was to apply compared to the duration targets (88.50%, 542.73 ms, 7.24 µV).
physiological measures of arousal and attention using EEG and ERP However,becausethedurationtaskwasmoredifficultorchallenging,
techniques to investigate the CNS nature of performance deficits participantsmayhaveexertedmoreeffortonthetask.Thisincreased
duringsleeprestriction.EEGtopographyshowedthatthebrainregions attention to or interest in the task might have increased P300
affectedbysleeplossweredynamicoverthecourseofsleeprestriction. amplitude,maskinganydecreasesduetosleeploss.
Specifically,quantitativeanalysisoftheEEGshowedthattherewere Both EEG and ERPs showed that deficits were more apparent at
significantdifferencesbetweenthe1stand7thdaysofsleeprestriction right-hemispheresites.Althoughthepatternofphysiologicalchange
withsignificantlineardecreasesinarousalatfrontalsites,depictingan in arousal and attention was similar for left-hemisphere sites, the
immediateandcontinuousreductioninphysiologicalalertnessover deficitsweremorestatistically robustin theright-hemisphere.This
thesleeprestrictionweek.However,atparietalsites,therewasrelative effect cannot be explained by the choice of reference for EEG
stability between the 1st and 4th days of restriction, with deficits recordingsbecauseanalysisoftheEEGandERPswascarriedouton
becoming apparent only later in the week, with a sharp decline data that was re-referenced to the average of A1 and A2 sites,
betweenthe4thand7thdaysofrestriction.Boththelineardeclinein effectivelycreatedabalanced,centralreference.Allparticipantsinthe
arousalovertheweekandthemoreprecipitousdropattheendofthe study were right-handed. Thus, one possibility is that the EEG
weekwasapparentatcentralsites.ThesedataprovidesupportforCNS laterality observed might be due to movement time or use of the
changes in arousal that underlie the oft-reported deficits in perfor- preferred right hand. However, no response or movement occurred
mance following sleep restriction. The immediate and continuous duringtheAATtaskwhenEEGdatawasrecorded,andresponsesto
deficitsapparentatfrontalEEGsitesareconsistentwiththehypothesis thetargettonesintheERPtasksweregivenwithahand-heldbutton