Institute of Chronobiology, Department of Psychiatry, New York
Hospital-Cornell Medical Center, White Plains, New York
It is generally acknowledged that changes in the
sleep/waking system accompany the aging process. Such changes are
expressed most clearly in the form of fragmented, shallow nocturnal
sleep, frequent, early morning awakenings and increased daytime
sleepiness. The extent to which such sleep alterations may be the
consequence of changes in the circadian timing system remains unclear.
However, the features that characterize sleep maintenance disturbance in
the elderly are consistent with circadian rhythms involvement and
growing evidence supports such a notion.
We recently reported that the circadian temperature
rhythms of older subjects are phase-advanced relative to young subjects
and that usual sleep times, as well as subjective sleep quality, were
correlated with the degree of phase advance (1). We have also reported
that healthy older subjects are exposed to remarkable little light of
sufficient intensity to entrain the human circadian system -- as little
as 45 minutes per 24 hours (2). Based on these findings, and on the
demonstrated phase-shifting effects of timed exposure to bright light,
we have been attempting to readjust the phase relationship between sleep
and body core temperature by exposing older, sleep-disturbed subjects to
artificial bright light. We hypothesized that such phase readjustment
would result in more consolidated nocturnal sleep and reduced daytime
METHODS: Subjects were
electrographically recorded for 4 consecutive nights prior to treatment
(2 Adaptation, 2 Baseline). Throughout the days following the last 2
nights in the lab, daytime sleepiness was assessed (Maintenance of
Wakefulness Test), as was cognitive and psychomotor performance. Body
core temperature was also continuously recorded during each subject's
stay in the lab. Treatment was then administered for 7 to 10 consecutive
days while subjects lived at home and continued their usual daily
activities. Active treatment consisted of sitting before a bank of
bright white lights (4000 to 5000 Lux) each day for two hours at a
designated time, based on temperature data obtained during Baseline
recordings. The control condition was identical except that subjects
were exposed to dim red illumination (< 50 Lux). Following treatment,
subjects again reported to the lab for 4 nights and 2 days, to repeat
the pre-treatment protocol. This is an ongoing study and the finding
reported here are based on the data of 6 subjects in the active
condition (mean age: 68.4) and 4 subjects (mean age: 71.3) in the
RESULTS: In response to
bright light exposure, subjects exhibited an average phase shift in body
core temperature of about 2 hours.
was no significant phase shift in body core temperature associated with
timed exposure to the dim red light. Because bedtimes and wakeup times
were only slightly delayed from baseline to post-treatment, the location
of the temperature minimum relative to the sleep period was altered
substantially in the bright light group. Prior to treatment, the fitted
minimum occurred an average of 23 minutes after the midpoint of sleep.
In contrast, following timed exposure to bright light, the minimum
occurred, on average, 112 minutes after the midpoint of sleep.
Significant improvements in sleep quality accompanied
the circadian rhythms adjustment in the bright light group. Because the
primary complaint in this sample was an inability to maintain,
rather than initiate sleep, perhaps the most important and revealing
variable examined was wake time after sleep onset (WASO).
On the Baseline nights, subjects in the bright light
group showed an average of 91.2 minutes WASO (SD = 36.6 min). On
post-treatment evaluation, WASO declined to 35.4 minutes (SD = 22.8 min)
(p = .003). As a result of the reduced time awake, sleep efficiency
showed a significant increase from Baseline to Post-Treatment (79.8% to
91.9%: p,.001). A further indication of improved sleep continuity was
reflected in the significant reduction in stage changes following bright
light exposure (p < .03). Wakefulness within sleep was replaced not only
by Stage 2 sleep, but also by substantial increases in slow wave sleep
(visually score Stages 3 and 4) and by REM sleep, as shown in the Figure
preliminary findings indicate that timed exposure to bright light is
highly effective in alleviating age-related sleep maintenance
disturbance. In addition to Stage 2, both SWS and REMS percentages
increased following treatment, probably because increased sleep
continuity "permitted" these sleep states to evolve with fewer
interruptions. Since improvement in sleep was associated with changes in
the circadian timing system (as reflected by a phase shift in
temperature) these data further suggest that the bright light treatment
acts directly on that system, perhaps by correcting the phase
relationship between body core temperature and the timing of sleep.
- Campbell, S, Gillin, J, Kripke, D, Erikson P and Clopton, P.
Sleep 12 (6): 529-536, 1989.
- Campbell, S, Kripke, D, Gillin, J and Hrubovcak, J.
Physiology and Behavior 42(2): 141-144, 1988.
Sleep Research (1991)20:448