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AN OLFACTORY STIMULUS MODIFIES NIGHTTIME SLEEP
IN YOUNG MEN AND WOMEN
Namni Goel, Hyungsoo Kim, and Raymund P. Lao
Department of Psychology, Wesleyan University, Middletown, Connecticut, USA
Aromatherapy is an anecdotal method for modifying sleep and mood. However,
whether olfactory exposure to essential oils affects night-time objective sleep remains
untested. Previous studies also demonstrate superior olfactory abilities in women.
Therefore, this study investigated the effects of an olfactory stimulus on subsequent
sleep and assessed gender differences in such effects. Thirty-one young healthy
sleepers (16 men and 15 women, aged 18 to 30 yr, mean +SD, 20.5 +2.4 yr)
completed 3 consecutive overnight sessions in a sleep laboratory: one adaptation, one
stimulus, and one control night (the latter 2 nights in counterbalanced order). Subjects
received an intermittent presentation (first 2 min of each 10 min interval) of an olfac-
tory (lavender oil) or a control (distilled water) stimulus between 23:10 and 23:40 h.
Standard polysomnographic sleep and self-rated sleepiness and mood data were
collected. Lavender increased the percentage of deep or slow-wave sleep (SWS) in
men and women. All subjects reported higher vigor the morning after lavender
exposure, corroborating the restorative SWS increase. Lavender also increased stage
2 (light) sleep, and decreased rapid-eye movement (REM) sleep and the amount of
time to reach wake after first falling asleep (wake after sleep onset latency) in
women, with opposite effects in men. Thus, lavender serves as a mild sedative and
has practical applications as a novel, nonphotic method for promoting deep sleep in
young men and women and for producing gender-dependent sleep effects.
Keywords Sleep, Mood, Nonphotic, Odor, Aromatherapy, Soporific, Gender
differences, Polysomnography, Sleepiness, POMS, Circadian
INTRODUCTION
Both biologic and nonbiologic olfactory stimuli modify circadian
rhythms (see reviews, Davidson and Menaker, 2003; Mistlberger and
Skene, 2004). However, evidence of such direct effects on the sleep-wake
cycle—a fundamental circadian rhythm partially controlled by the
Submitted May 9, 2005, Returned for revision June 25, 2005, Accepted July 15, 2005
Address correspondence to Namni Goel, PhD, Department of Psychology, 207 High Street, Judd
Hall, Wesleyan University, Middletown, CT 06459, USA. E-mail: ngoel@wesleyan.edu
Chronobiology International, 22(5): 889–904, (2005)
Copyright #2005 Taylor & Francis, Inc.
ISSN 0742-0528 print/1525-6073 online
DOI: 10.1080/07420520500263276
889
circadian clock—is lacking. Therefore, this study explores the effects of
lavender oil, a common odor, on night-time sleep and morning alertness.
Aromatherapy’s physiological and psychological effects, produced by
pure plant or essential oils, are acknowledged worldwide in folk medicine
and health care (Buckle, 2001; Price and Price, 1999; Tisserand, 1988).
Aromatherapy claims significant effects on sleep and mood (Price and
Price, 1999), although such evidence is predominantly anecdotal, deriving
from small trials and case studies (Buckle, 2001; Gyllenhaal et al., 2000).
Indeed, the effects of aromatherapy on human sleep remain untested
under controlled laboratory conditions.
Olfactory stimuli such as peppermint and pyridine, when presented
during sleep, produce physiological responses in young adults, despite a
reduced arousal threshold during sleep compared with waking (Badia
et al., 1990; Carskadon and Herz, 2004). Several other studies report
improved sleep—including decreased time awake, increased total time
asleep, and reduced daytime sleepiness—following lavender presentation
before and during sleep in elderly and demented subjects (Hardy, 1991;
Henry et al., 1994; Hudson, 1996; Wolfe and Herzberg, 1996). Other
essential oils have produced similar effects in young and older adults
(Connell et al., 2001; Raudenbush et al., 2003; Sano et al., 1998;
Svoboda et al., 2002). However, these studies were uncontrolled, had
small sample sizes, and used subjective evaluations. Thus, further investi-
gations are necessary to determine the effects of odors on objective sleep.
Beyond sleep, lavender’s sedative and calming effects have been noted
using various physiological measures during waking. Lavender lowers
heart rate and blood pressure (Nagai et al., 2000; Romine et al., 1999)
and changes electroencephalographic (EEG) frequency and contingent
negative variation (Torii et al., 1988), suggesting increased drowsiness.
Lavender also increases beta activity (Diego et al., 1998; Lorig et al.,
1990), decreases alpha activity (Masago et al., 2000), and increases theta
activity (Klemm et al., 1992; Lorig and Schwartz, 1988). Such findings
concur with self-reported relaxing mood states induced by lavender
exposure (Diego et al., 1998; Goel and Grasso, 2004; Motomura et al.,
2001). In addition, lavender slows reaction times (Karamat et al., 1992;
Yagyu, 1994) and reduces performance of cognitive tasks (Ludvigson
and Rottman, 1989; but see Diego et al., 1998).
According to the homeostatic function of sleep, sleep represents in
part, a recovery period following the cumulative increase in physiological
strain during wakefulness (Borbe
´ly, 1982). Providing support for this
theory, various sensory stimuli or behavioral events experienced before
bedtime modify subsequent sleep by increasing deep or slow-wave sleep
(SWS). SWS increases following auditory (Cantero et al., 2002; Fruhstorfer
et al., 1984, 1988) and visual stimulus exposure (Horne and Walmsley,
1976). Similarly, exercise increases nighttime SWS (e.g., Bunnell et al.,
N. Goel, H. Kim, and R. P. Lao890
1983; Horne and Staff, 1983; Horne and Moore, 1985; Youngstedt et al.,
1997), as does body warming (Bunnell et al., 1988; Dorsey et al., 1999;
Horne and Reid, 1985; Sung and Tochihara, 2000). Thus, lavender
odor may share a common mechanism with other sensory stimuli for
promoting SWS (Garcı´a-Garcı´a et al., 1998).
Gender differences in olfactory performance have been examined
widely, in which women generally show superior abilities (see reviews in
Brand and Millot, 2001; Velle, 1987). Odors also produce greater physio-
logical responses in women than in men (Becker et al., 1993; Evans et al.,
1995; Henkin and Levy, 2001; Levy et al., 1999; Yousem et al., 1999, see
Bengtsson et al., 2001; Levy et al., 1997).
This experiment investigated the effects of commercially available laven-
der oil on subsequent polysomnographic (PSG) sleep in healthy young men
and women. We hypothesized that lavender would promote sleep by
increasing SWS (in a manner similar to other sensory stimuli) and by short-
ening sleep onset latency when presented before bedtime. We also pre-
dicted that lavender would produce gender-differentiated effects, with
larger PSG changes in women. Finally, we predicted that lavender would
increase sleepiness and fatigue and decrease vigor at bedtime.
MATERIALS AND METHODS
Participants
Thirty-one subjects, 16 men and 15 women, ages 18 to 30 yr (overall
mean age +SD, 20.5 +2.4 yr; men: 20.2 +2.9 yr; women: 20.8 +1.8 yr)
participated. Subjects were recruited through local newspaper advertise-
ments and campus postings and were screened by telephone and
in-person interviews. These interviews ascertained that all subjects were
in good physical and psychological health, were healthy sleepers, were
not using central nervous system medications, and had no history of
respiratory disease such as chronic asthma or sinus problems. Subjects
with extreme morningness or eveningness, assessed by the Morningness-
Eveningness Questionnaire (Horne and O
¨stberg, 1976), were excluded.
To test olfactory function, subjects were exposed to several odors and
water and asked whether they could detect each. Those with detection dif-
ficulties were excluded. This supra-threshold detection approach ensured
that each subject had a similar minimal level of olfactory functioning and
avoided possible expectancy effects that may emerge with sub-threshold
concentrations (Campenni et al., 2004; Torii et al., 1988).
Three women were taking oral contraceptives, and all women had
normal menstrual cycles. An equal number of women were in their
luteal (n¼6) or follicular (n¼6) menstrual cycle phases. Although
smokers were not excluded, only 3 subjects (2 men, 1 woman) had a
Olfactory Stimulus Modifies Sleep 891
history of smoking. Subjects maintained a stable wake-up time and
bedtime, documented by sleep logs for 1 wk before study entry. Wesleyan
University’s Institutional Review Board approved the study, and all pro-
cedures conformed to the Declaration of Helsinki and to the ethical and
good practice standards for biological rhythm research as advanced by
the Journal (Touitou et al., 2004). Subjects received monetary compen-
sation for participation and signed informed consent before study entry.
Polysomnographic Recordings
Central and occipital electroencephalographic (EEG), electrooculo-
graphic (EOG), and submental electromyographic (EMG) measures were
recorded from 24 : 00 (lights off) to 08:00 h (lights on). During the adap-
tation night, subjects were screened for sleep pathologies, including
apneas, oxygen desaturation, and periodic limb movements by monitoring
respiratory effort, nasal airflow, arterial oxygen saturation level, bilateral
anterior tibialis EMG, and heart rate (EKG). Sleep records were visually
scored in 30sec epochs according to Rechtschaffen and Kales’ (1968)
standard scoring criteria by two trained scorers blind to the experimental
conditions. Inter-rater reliability for the two scorers was 95.2%. Sleep par-
ameters for the whole night and for the first (24:00 to 04:00h) and second
(04:00 to 08:00h) half of the stimulus and control nights were analyzed.
Subjective Sleepiness and Mood Questionnaires
The Stanford Sleepiness Scale (SSS; Hoddes et al., 1973) quantifies the
progressive, subjective stages of the sleep-alertness continuum, with a scale
from 1 to 7 (1: feeling active, vital, alert, or wide awake; 7: sleep onset soon,
lost struggle to remain awake). The SSS has been tested with repeated
acute sampling periods (e.g., 15 min).
The Profile of Mood States Questionnaire (POMS; McNair et al.,
1992), a 65-item self-report scale, assesses transient affective states in
response to various stimuli including olfactory cues ( Jacob and McClintock,
2000; Jacob et al., 2001; Schiffman et al., 1995). The POMS has been
validated in repeated measures designs (reviewed in Schiffman et al.,
1995) and sleep studies (Dollins et al., 1994; Jockovich et al., 2000;
Wright et al., 1998). Moreover, it has been tested with repeated acute
sampling periods (e.g., 3 min; McNair et al., 1992). Each item is rated on
a scale from 0 to 4 (0: not at all; 4: extremely), on each of 6 factors:
depression-dejection (Depression), tension-anxiety (Tension), anger-
hostility (Anger), confusion-bewilderment (Confusion), vigor-activity
(Vigor), and fatigue-inertia (Fatigue). The total score for each factor is cal-
culated by adding together the respective set of adjectives corresponding
to that factor. The total mood disturbance score (TMD), a global estimate
N. Goel, H. Kim, and R. P. Lao892
of affective state, derives from summing the factors together, with vigor-
activity weighted negatively.
Odor
The olfactory stimulus was commercially available lavender oil (Inter-
national Fragrance and Technology, Inc., Canton, Georgia, USA). The
lavender oil contained a natural lavender base component to which con-
stituents were added; it did not contain solvent materials (verified by gas
chromatography). This particular lavender oil was validated externally
as a sedative in a previous study of subjects recruited from the same
college population; in that study, lavender increased fatigue and confusion
and decreased vigor compared with distilled water (Goel and Grasso,
2004). Lavender has been rated as neutral to mildly pleasant on pleasant-
ness scales and is neutral on familiarity, intensity, and irritability scales
(Knasko, 1992; Levick et al., 1993; Millot and Brand, 2001; Millot et al.,
2002; Royet et al., 2000; Savic and Berglund, 2000; Savic and Gulyas,
2000; Zatorre et al., 1992). Distilled water served as the control.
Procedure
Subjects slept in a sleep laboratory for 3 consecutive overnight sessions
(Figure 1). Each session lasted from approximately 21:00 to 08:00 h. On
FIGURE 1 Schematic representation of the 3 consecutive night study protocol.
Olfactory Stimulus Modifies Sleep 893
the second and third intervening days, subjects left the laboratory between
08:00 to 21:00 h and engaged in their habitual activities. On these study
days, subjects refrained from napping and exercise, and from alcohol or
caffeine intake. In addition, subjects were not allowed to wear scented pro-
ducts (e.g., perfume, lotion) or to eat or drink for at least 1 h before test
sessions.
Electrode placement for PSG recordings occurred at 21:00 h on all
nights. Subjects then engaged in recreational activities until bedtime
(24:00 h) on the first night and until 23:10 h on the second and third
nights. PSG data were collected from 24:00 to 08:00 h each night. Subjects
remained in bed if they awakened before 08:00 h.
The first night served as an adaptation session. During the second and
third nights, subjects received either lavender essential oil or distilled
water from approximately 23:10 to 23:40 h. Subjects were not told what
odors they were receiving, nor were they informed about the odors’ inten-
sity, hedonics, or stimulating/sedating properties. They also were not told
that one of the vials contained water. The session order was counter-
balanced; furthermore, gender was counterbalanced within order assign-
ment. Of the 31 subjects, 16 (9 men, 7 women) received the odor first
and 15 (7 men, 8 women) received the control first.
During the experimental session, subjects received lavender oil inter-
mittently between 23:10 and 23:40 h. The stimulus was presented for
the first 2 min of each 10 min period (23:10, 23:20, 23:30, and 23:40 h).
Subjects held the lavender vial at chest level, and breathed normally and
steadily with their eyes closed. The experimenter ensured that subjects
remained awake and that no other competing stimuli were present
during odor exposure. The control session was identical to the experi-
mental session except that subjects held and smelled a vial containing
distilled water. The various components of this experimental procedure,
including intermittent odor exposure, the odor administration technique,
and use of water as a control have been used previously (Goel and
Grasso, 2004; Ilmberger et al., 2001; Kline et al., 2000; Lao et al., 2004).
The SSS was administered at 23:50 and 08:00 h on all 3 nights; the
POMS was administered at 23:00, 23:12, 23:42, and 08:00 h on the
stimulus and control nights. These instruments are designed for repeated
measures over short time intervals, as noted above; moreover, any possible
repeated administration effects would be observed in both the lavender
and control sessions.
Statistical Analyses
Repeated measures analyses of variance (ANOVA), with gender and
session order as between-subject factors, examined differences in PSG mea-
sures and SSS and POMS scores between the two sessions. A companion
N. Goel, H. Kim, and R. P. Lao894
manuscript in this journal issue reports on the 3-night analyses (including
the adaptation night) for these measures, highlighting robust gender
differences (Goel et al., 2005). Post-hoc tests, corrected for multiple
comparisons, examined significant interactions for all measures. The mag-
nitude of between-group differences in scores was expressed as effect
size, d, the standardized difference between means (d¼0.3, small; 0.5,
medium; 0.8, large; Cohen, 1988). Data are presented as mean +SD;
p,0.05 was considered significant for all statistical analyses.
RESULTS
Polysomnographic (PSG) Sleep
Session Order Differences
There were no significant session order (stimulus-control vs. control-
stimulus) differences in PSG measures for the whole night, or for the
first or second half of the night. Furthermore, there were no significant
session order gender interactions for any PSG measure.
Session Differences
Across the whole night, lavender significantly increased deep or SWS
(stages 3 and 4) %sleep period time (the duration from sleep onset to the
end of sleep; SPT) compared with the control (F
1,27
¼10.41, p,0.005,
d¼0.29; Table 1). Similarly, during the first half of the night, SWS
%SPT was significantly higher following lavender exposure (13.3% +
7.7% vs. 11.5% +8.5%; F
1,27
¼4.79, p,0.05, d¼0.22). More specifically,
lavender significantly increased SWS duration during the first NREM-
REM cycle (NREM sleep followed immediately by rapid eye movement
[REM] sleep; 24.5 +16.0 vs. 20.4 +15.6 min; F
1,27
¼4.33, p,0.05,
d¼0.26). Although there were no significant session differences in sleep
measures for the second half of the night, SWS %SPT showed a trend
toward significance in the same direction as that for the first half of the
night (0.9% +1.8% vs. 0.4% +0.5%; F
1,27
¼3.24, p¼0.08, d¼0.40).
Session Gender Differences
Across the whole night, wake after sleep onset (WASO) latency (the time
to reach wake after first falling asleep) showed a significant session
gender interaction (F
1,10
¼10.07, p,0.01; Table 1): compared with the
control, lavender decreased WASO latency in women, while increasing
WASO latency in men. WASO latency did not differ significantly between
sessions for either gender (men, t
8
¼0.38, p¼0.71, d¼0.02; women,
Olfactory Stimulus Modifies Sleep 895
TABLE 1 Mean +SD Whole Night Sleep Measures for the Stimulus and Control Nights
PSG measure
Stimulus night Control night
Men Women Total Men Women Total
Total sleep time (TST), min 453.7 +29.2 467.9 +13.3 460.6 +23.7 451.0 +27.1 463.4 +20.7 457.0 +24.6
Sleep period time (SPT), min
a
460.8 +23.1 471.5 +7.1 466.0 +17.8 456.6 +26.3 469.2 +9.0 462.7 +20.6
Total wake time (TWT), min 26.1 +29.4 9.9 +12.1 18.2 +23.9 27.9 +25.7 14.9 +20.0 21.6 +23.7
Sleep efficiency (SE), % 94.6 +6.1 97.8 +2.6 96.1 +5.0 94.2 +5.4 96.8 +4.2 95.5 +5.0
Sleep maintenance efficiency (SME), % 98.4 +3.1 99.3 +2.3 98.8 +2.7 98.8 +1.6 98.7 +2.8 98.8 +2.2
Sleep onset latency (SOL), min 18.5 +23.6 5.9 +5.3 12.4 +18.2 22.5 +24.7 9.2 +8.4 16.0 +19.6
Wake after sleep onset (WASO), %SPT 1.7 +3.0 0.8 +2.3 1.2 +2.7 1.2 +1.6 1.3 +2.8 1.2 +2.2
WASO, latency, min
b
245.3 +112.3 94.9 +88.0 191.6 +125.4 243.3 +113.0 186.6 +156.7 223.6 +129.2
Stage 1, %SPT 2.7 +2.5 1.7 +1.6 2.2 +2.1 2.6 +1.3 3.4 +4.4 3.0 +3.2
Stage 1, latency, min 18.4 +23.6 5.9 +5.3 12.4 +18.2 23.0 +24.6 31.4 +84.8 27.1 +60.7
Stage 2, %SPT 65.6 +5.0 66.8 +7.0 66.2 +6.0 67.9 +4.6 64.7 +8.4 66.3 +6.8
Stage 2, latency, min 23.9 +25.0 9.4 +5.3 16.9 +19.5 25.5 +25.6 13.8 +10.8 19.8 +20.4
Slow-wave sleep (SWS; Stages 3 þ4), SPT
c
6.8 +3.9 7.1 +4.4 6.9 +4.1 5.6 +3.8 5.8 +4.8 5.7 +4.2
SWS (Stages 3 þ4), latency, min 58.3 +32.1 41.9 +13.1 50.4 +25.8 64.9 +45.9 49.0 +19.2 57.2 +35.9
Non-rapid eye movement (NREM), %SPT 75.2 +5.7 75.6 +5.4 75.4 +5.5 76.2 +6.6 73.9 +4.2 75.1 +5.6
Rapid-eye movement (REM), %SPT 23.2 +5.6 23.7 +5.3 23.4 +5.4 22.6 +6.5 24.9 +2.9 23.7 +5.1
REM, latency, min 114.4 +46.7 101.8 +53.4 108.3 +49.6 128.4 +75.3 95.3 +37.3 112.4 +61.4
a
SPT is defined as the duration from sleep onset to the end of sleep.
b
Significant session gender interaction for the stimulus and control nights (p,0.01).
c
Significant session effect for the stimulus and control nights (p,0.005).
896
t
4
¼1.00, p¼0.38, d¼0.68), although women showed a significantly
shorter WASO latency with lavender (F
1,13
¼6.62, p,0.05; d¼1.44).
In the first half of the night, stage 2 %SPT showed a significant
session gender interaction (F
1,27
¼14.34, p,0.001): compared with
the water control, lavender reduced stage 2 %SPT in men (t
15
¼4.41,
p,0.001, d¼0.90; Figure 2A), but not in women (t
14
¼1.22, p¼0.24,
d¼0.23). REM %SPT also showed a significant session gender inter-
action (F
1,27
¼7.25, p,0.05): compared with water, lavender significantly
increased REM %SPT in men (t
15
¼2.10, p,0.05, d¼0.54; Figure 2B),
but not in women (t
14
¼1.42, p¼0.18, d¼0.51). There were no signifi-
cant interactions in PSG measures in the second half of the night.
Subjective Sleepiness and Mood
Vigor showed a significant session time interaction (F
3,66
¼3.93,
p,0.05), with higher scores at 08:00 h in the lavender than control
session (t
26
¼2.44, p,0.05, d¼0.32; Figure 3). There were no other sig-
nificant POMS differences. SSS scores did not differ significantly between
the lavender and control sessions, between the morning and evening, or
between men and women.
DISCUSSION
This study demonstrates sleep-promoting effects of lavender odor in
young healthy male and female sleepers. Lavender produced small but
FIGURE 2 Significant session gender interactions in the first half of the night for (A) Stage 2 %SPT
and (B) REM %SPT (mean +SD). Men showed significant differences in these measures between the
control and stimulus nights (¼p,0.05; ¼p,0.001).
Olfactory Stimulus Modifies Sleep 897
significant increases in SWS or deep sleep in all subjects, with higher vigor
the morning following exposure. In addition, lavender produced gender-
differentiated effects on stage 2 and REM sleep, and WASO latency, under-
scoring gender as an important variable for future sleep research using
young populations.
The predicted SWS increase corroborates previous reports of
improved sleep quality following exposure to lavender (Hardy, 1991;
Henry et al., 1994; Hudson, 1996; Wolfe and Herzberg, 1996) or other
odors (Connell et al., 2001; Raudenbush et al., 2003; Sano et al., 1998;
Svoboda et al., 2002). While these earlier studies contained methodological
drawbacks, our results demonstrate lavender’s sleep-promoting effects
using a larger sample and objective sleep measures. Furthermore, the
SWS increase, indicating lavender’s sedative properties, concurs with
lavender-induced reductions in blood pressure and heart rate (Nagai
et al., 2000; Romine et al., 1999). In contrast to our prediction, however,
lavender did not shorten sleep onset latency. Since all subjects were
healthy sleepers, who on average fell asleep approximately 15 min after
lights off, the short sleep latencies may have precluded detection of
lavender-induced changes.
Lavender likely would substantially affect sleep onset latency, and thus
perhaps the circadian timing of sleep, in subjects with initial insomnia or in
older adults. Indeed, other mild nonpharmacologic sedatives, such as
valerian, show individual differences in effectiveness, with greater
responses in habitually poor or irregular sleepers, including the elderly
FIGURE 3 Vigor POMS scores across assessment time points for the stimulus and control nights
(mean +SD). Significantly greater than the control night, p,0.05.
N. Goel, H. Kim, and R. P. Lao898
(Leathwood and Chauffard, 1982). Beyond these groups, lavender also
may benefit depressed subjects who characteristically show reductions in
SWS, along with other sleep changes (Benca et al., 1992). Certainly,
depressed young adults show a heightened ability to discriminate lavender
(Goel and Grasso, 2004). Finally, lavender may be used to promote sleep in
critically ill or hospitalized patients, two groups that have shown benefit
from aromatherapy (Richards et al., 2003; Waldman et al., 1993).
Increases in SWS %SPT were found during the first, but not the second
half of the night, and were found predominantly during the first
NREM-REM cycle, suggesting that lavender’s effects on deep sleep do
not persist throughout the night. Given its route of administration, laven-
der likely is absorbed quickly, exerting immediate but transient effects.
Moreover, a lack of morning sleepiness score changes suggests that laven-
der does not produce “hangover” effects the next day.
The significant session gender interactions for WASO latency, stage
2 %SPT, and REM %SPT may reflect differences in odor abilities
between men and women, as supported by other studies (see reviews,
Brand and Millot, 2001; Velle, 1987). Specifically, neural activation differ-
ences may explain the contrasting changes in these sleep measures
observed between men and women. Indeed, odors activate different struc-
tures (Savic et al., 2001) or produce greater responses in women (Becker
et al., 1993; Evans et al., 1995; Henkin and Levy, 2001; Levy et al., 1999;
Yousem et al., 1999) than in men (Levy et al., 1997). There also may be
chemical (systemic/non-perceptual) gender differences for lavender, or
inhalation and dosing differences, since we did not control breathing
rates. In contrast with sleep changes, lavender did not produce gender-
differentiated mood changes, concurring with our earlier study using the
same odor and self-rated questionnaire (Goel and Grasso, 2004). Thus,
our results suggest that the gender-differentiated sleep responses may be
mediated by physiological rather than psychological mechanisms.
Lavender increased vigor the morning following exposure, corroborat-
ing the increase in restful deep sleep. By contrast, POMS changes were not
detected immediately following exposure at 23:42 h. The absence of such
immediate changes, including in vigor and fatigue, contrasts another study
in which lavender increased fatigue, anxiety, anger, confusion, and total
mood disturbance, and decreased vigor compared with distilled water
(Goel and Grasso, 2004). Our results also contrast with studies that found
lavender decreased tension/anxiety (Dunn et al., 1995; Itai et al., 2000;
Kawai and Noro, 1996; Louis and Kowalski, 2002), improved mood
(Dunn et al., 1995; Knasko, 1992), and reduced total mood disturbance
(Diego et al., 1998) and stress (Motomura et al., 2001). Such differences
may be due to lavender administration time or exposure duration.
Similarly, lavender did not affect subjective sleepiness before bedtime.
Other mild sedatives, such as melatonin, also produce changes in objective
Olfactory Stimulus Modifies Sleep 899
sleep without SSS changes (Pires et al., 2001; Zhandova et al., 1995; but see
Dollins et al., 1994). Our results may seem inconsistent with previous find-
ings indicating immediate physiological, including EEG, changes following
lavender exposure (Diego et al., 1998; Klemm et al., 1992). Such discre-
pant results may reflect the inaccuracy of self-rated evaluations or the
possibility that lavender produces physiological changes without aware-
ness by the subjects.
Overall, our findings are consistent with previous studies suggesting
that sensory stimulation or salient behavioral experiences occurring
during wakefulness affect subsequent sleep by modulating the neural struc-
tures regulating sleep-wake cycles (Cantero et al., 2002; Drucker-Colin,
1995; Garcı´a-Garcı´a et al., 1998; Velluti, 1997). Indeed, all of the following
stimuli also increase SWS: auditory cues (Cantero et al., 2002; Fruhstorfer
et al., 1984, 1988); visual cues (Horne and Walmsley 1976); exercise (e.g.,
Bunnell et al., 1983; Horne and Moore, 1985; Horne and Staff, 1983;
Youngstedt et al., 1997), and body warming (Bunnell et al., 1988; Dorsey
et al., 1999; Horne and Reid, 1985; Sung and Tochihara, 2000). Thus,
olfactory cues may share a common mechanism with other behavioral
and sensory stimuli for modulating the release of specific sleep-inducing
substances that promote deep sleep (Garcı´a-Garcı´a et al., 1998).
Lavender modulates intracellular cyclic adenosine monophosphate
(cAMP) activity (Lis-Balchin and Hart, 1999), and its principal component,
linalool, inhibits glutamate binding; both factors may produce sedative
effects (Elisabetsky et al., 1995). The neuroanatomical pathways mediating
lavender’s sedative sleep effects, however, remain unknown. All odors,
including lavender, activate the primary olfactory cortex and its neural
connections, including the amygdala, anterior cingulate, claustrum, and
the piriform, entorhinal, insular, and orbitofrontal cortices (see Bengtsson
et al., 2001; Levy et al., 1997, 1999; Royet et al., 2000; Savic and Gulyas,
2000; Zatorre et al., 1992). These olfactory targets may subsequently trans-
duce information to the various brain centers implicated in the control of
the sleep-wake cycle, including its circadian component. Alternatively,
lavender may exert its effects systemically through the blood after entry
into the nasal passages.
This is the first study to examine the effects of an olfactory stimulus
presented before bedtime on subsequent objective sleep. In all subjects,
lavender odor produced increases in SWS compared with the control,
and increased vigor the next morning. Lavender also showed differential
gender effects for WASO latency, stage 2, and REM sleep: it increased
stage 2 and decreased REM sleep and WASO latency in women, but pro-
duced the opposite effects in men. Our results have practical applications
and merit future studies. Commercially available lavender oil may be
used as a mild soporific and a nonphotic alternative or safe adjunctive
(Atanassova-Shopova and Roussinov, 1970) to other substances, such as
N. Goel, H. Kim, and R. P. Lao900
valerian or melatonin, for relieving mild sleep disturbance. Other essential
oils that also are natural sedatives, such as chamomile, may produce
similar sleep effects; by contrast, stimulating odors such as jasmine, may
disrupt sleep (Gyllenhaal et al., 2000). Aromatherapy shows promise for
modifying sleep and perhaps its circadian timing in various populations,
including insomniacs, depressed patients, and the elderly.
ACKNOWLEDGMENTS
This research was supported by a grant from the Sense of Smell
Institute (N.G.). R.P. Lao received summer support from a Howard
Hughes Medical Institute grant for undergraduate education at Wesleyan
University. We thank Dave Bushnell, Glenda Etwaroo, Ying-Ju Lai, and
Sonia Vesely for assistance in data collection. We also are grateful to
Dr. Albert Fry for his invaluable assistance in the gas chromatography
analysis of the lavender oil.
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