SLEEP 2011 Abstract Supplement

A. Basic Science VI. Chronobiology
0149
INTERACTIONS BETWEEN TIME-ON-TASK, SLEEP
HOMEOSTATIC AND CIRCADIAN PROCESSES ON VISUAL
VIGILANCE
Burke TM 1 , Scheer FA 2 , Ronda JM 2 , Czeisler CA 2 , Wright KP 1,2
1
Integrative Physiology, Univeristy of Colorado at Boulder, Boulder,
CO, USA, 2 Division of Sleep Medicine, Department of Medicine,
Brigham and Women’s Hospital, Harvard Medical School, Boston,
MA, USA
Introduction: Vigilance performance is well known to be modulated
by time awake, circadian phase and time-on-task, but whether and how
these three factors interact is not known. Therefore, we examined how
time-on-task decrements in visual vigilance performance interact with
time awake and circadian phase using a 20-min Psychomotor Vigilance
Task (PVT-20) assessed during a forced desynchrony protocol (FD).
Methods: Six healthy subjects [5 males (26.8±5.2yr;mean±SD)] were
studied in a 28-h FD for 12 days. PVT-20 performance was completed
near scheduled wake time and every 2h thereafter until 18h of scheduled
wakefulness. Time-on-task decrements in the reciprocal mean reaction
time were calculated for 2-min bins across the 20-min task. Data were
averaged into 60° circadian bins, with temperature minimum assigned
0°, and into 2-h time awake bins. The primary analysis compared timeon-task
decrements at 2h and 18h awake across circadian phase using
repeated measure ANOVA.
Results: Significant interaction effects between time awake and circadian
phase, between time-on-task and hours awake and between timeon-task
and circadian phase were observed (all p < 0.05). In general,
time-on-task decrements in performance were greater at 18h awake
compared to 2h awake. In addition, time-on-task decrements in performance
at 2h awake were similar for all circadian phases examined,
whereas time-on-task decrements in performance at 18h awake were
larger between 0-180 circadian degrees compared to 240-300 circadian
degrees after 4 min time-on-task.
Conclusion: Time-on-task, time awake and circadian phase each modulate
visual vigilance with greater impairments due to time-on-task when
sleep homeostatic and circadian drives for sleep were high. Impairments
in visual vigilance are greater after 4min time-on-task at 18h awake and
misalignment of circadian phase. These findings have important implications
for shift workers required to maintain sustained attention during
round-the-clock operations.
Support (If Any): NIH R01-NS41886, by NASA Cooperation Agreement
NCC 9-58 with the National Space Biomedical Research Institute
(NSBRI), by NSBRI HFP00002, and the National Centers for Research
Resources NIH M01-RR02635
0150
CIRCADIAN REGULATION BEWARE, THERE’S
HOMEOSTATIC PRESSURE FOR SLEEP IN THE AIR
Paech GM 1 , Ferguson SA 1 , Sargent C 1 , Darwent D 1 , Matthews RW 1 ,
Heath G 1 , Kennaway DJ 2 , Roach GD 1
1
Centre for Sleep Research, University of South Australia, Adelaide,
SA, Australia, 2 Robinson Institute, Research Centre for Reproductive
Health, Discipline of Obstetrics and Gynaecology, University of
Adelaide, Adelaide, SA, Australia
Introduction: In the absence of sleep restriction (equivalent to 8h/24h),
REM sleep and sleep efficiency demonstrate circadian modulation.
There is some evidence suggesting that under conditions of severe sleep
restriction (equivalent to 4h/24h) the homeostatic drive for sleep overrides
the circadian drive for REM sleep and sleep efficiency. However, it
is unknown how the circadian and homeostatic processes influence sleep
under conditions of moderate sleep restriction (equivalent to 6h/24h).
The current study investigated the relative contributions of the circadian
and homeostatic processes on REM and sleep efficiency using a forced
desynchrony (FD) protocol with moderate sleep restriction.
Methods: Fourteen males (23.6±4.0yr) lived in a sleep laboratory free
from time cues for 12 days. Participants were scheduled to 3x24h baseline
days (8h sleep, 16h wake) followed by 7x28h FD days (7h sleep,
21h wake). Sleep was measured using standard polysomnography.
Core body temperature (CBT) was recorded continuously using a rectal
thermistor. Each epoch of sleep was assigned a circadian phase based on
the CBT data (6x60 degree bins) and an elapsed time into sleep episode
(4x105min intervals).
Results: Linear mixed model analyses showed a significant main effect
of circadian phase on the percentage of REM sleep and sleep efficiency.
Both REM sleep and sleep efficiency were highest around the circadian
nadir and lowest around the acrophase. There was a significant main
effect of elapsed time on the percentage of REM sleep and sleep efficiency.
Sleep efficiency decreased across the sleep episode whilst the
percentage of REM sleep increased.
Conclusion: Previous research has demonstrated the circadian modulation
of sleep in the absence of sleep restriction. Results from the current
study demonstrate that despite a moderate increase in homeostatic
pressure, the circadian modulation of REM sleep and sleep efficiency
persists. This highlights the complex interactions between the circadian
and homeostatic process on sleep regulation.
Support (If Any): This study was financially supported by the Australian
Research Council.
0151
TRAIT- AND STATE-DEPENDENT CHARACTERISTICS OF
SLOW-WAVE OSCILLATIONS DURING NREM SLEEP IN
MORNING AND EVENING CHRONOTYPES
Mongrain V 1,2 , Carrier J 1,3 , Paquet J 1 , Bélanger-Nelson E 1 ,
Dumont M 1,2
1
Center for Advanced Research in Sleep Medicine, Sacre-Coeur
Hospital of Montreal, Montreal, QC, Canada, 2 Psychiatry, Université
de Montréal, Montréal, QC, Canada, 3 Psychology, Université de
Montréal, Montréal, QC, Canada
Introduction: Slow-wave oscillations (SWO, 75µV) during
non-rapid eye movement (NREM) sleep are characterized by a negative
phase, during which cortical neurons are mostly silent, and a positive
phase, during which cortical neurons fire intensively. Longer duration
of wakefulness (i.e., higher sleep pressure) associates with higher SWO
density, amplitude and steeper slope between the negative and positive
peaks. Spectral analysis data suggest that Morning-types show faster
build-up and decay rates of sleep pressure compared to Evening-types.
We thus hypothesized that SWO characteristics will show larger changes
in Morning-types than in Evening-types in response to increased sleep
pressure.
Methods: Morning-types (n=12, 6 men) were compared to Eveningtypes
(n=12, 6 men) for a baseline sleep episode (BL) and for recovery
sleep (REC) after two nights of sleep fragmentation. Artefact-free epochs
recorded from the Fz derivation in NREM sleep were submitted to
SWO detection according to published criteria. SWO density (number
of SWO per minute of NREM sleep) and SWO characteristics (amplitude,
duration of negative and positive phases, slope between the negative
and positive peaks) were averaged for all-night NREM sleep and
per NREM period.
Results: SWO slope was steeper in Morning-types than Evening-types,
particularly in the first two NREM periods and during REC. Morningtypes
showed higher SWO amplitude than Evening-types, which difference
was significant only during REC. SWO positive and negative phase
durations were shorter in Morning-types than Evening-types but these
differences were constant across NREM periods and between the two
nights. SWO density did not differ between the groups.
Conclusion: Our data suggest that specific properties of cortical synchronization
during sleep differ between Morning-types and Eveningtypes,
although both chronotypes show similar SWO density. These
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SLEEP, Volume 34, Abstract Supplement, 2011