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Physiological and psychological effects of olfactory stimulation with D-Limonene

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Although D-Limonene can be considered an important component of nature-based stimuli, the physiological effects of olfactory stimulation with D-Limonene have not been completely clarified by scientific studies. The physiological and psychological effects of olfactory stimulation with D-Limonene were studied measuring heart rate variability (HRV), heart rate, and subjective evaluation using a modified semantic differential method; thirteen Japanese female university students (mean age±SD, 21.5±1.0 years) participated in the study. A concentration of 60 μL of D-Limonene was used as olfactory stimulant and room air as control. Subjects were exposed for 90 s while sitting with eyes closed. During D-Limonene inhalation: (1) the high-frequency (HF) value of HRV, a marker of parasympathetic nervous activity that is enhanced in relaxing situations, was significantly higher; (2) the heart rate was significantly lower; and (3) subjects reported feeling significantly more comfortable during D-Limonene administration than control. The results obtained clearly indicate that olfactory stimulation with D-Limonene induced physiologicaling important scientific evidence of the health benefits of D-Limonene.
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1. Introduction
In the modern age, people are forced to lead busy lives
and are exposed to a state of stress (Lederbogen et al.,
2011). Thus, measures to prevent and relieve this stress
state are urgently needed.
Recently, forest therapy has emerged as a method to
address stress states, and much data on the physiological
and psychological relaxing effects of forest environments
have been accumulated. Previous studies have reported
that viewing forest scenery or walking in forests can:
increase parasympathetic nervous activity, which is en-
hanced in relaxing situations and suppresses sympathetic
nervous activity which is increased in stress states (Tsu-
netsugu et al., 2007; Park et al., 2008; Lee et al., 2009;
Park et al., 2009; Park et al., 2010; Lee et al., 2011; Park
et al., 2012; Tsunetsugu et al., 2013; Lee et al., 2014); de-
crease cerebral blood flow in the prefrontal cortex (Park et
al., 2007); and decrease salivary cortisol concentration of
stress hormone (Tsunetsugu et al., 2007; Park et al., 2007;
Park et al., 2008; Lee et al., 2009; Park et al., 2010). In
addition, visiting a forest enhanced natural killer-cell ac-
tivity and improved immune function (Li et al., 2007; Li
et al., 2008 a, b, c) and the effect lasted 30 days (Li et
al., 2008 b). In subjective evaluations, it was reported that
people feel more “comfortable,” “soothed,” and “natu-
ral” when experiencing a forest environment (Park et al.,
2007; Tsunetsugu et al., 2007; Park et al., 2008; Lee et
al., 2009; Park et al., 2009; Lee et al., 2011; Park et al.,
2011; Tsunetsugu et al., 2013; Lee et al., 2014), and that
the “tension-anxiety,” “depression,” “anger-hostility,” “fa-
tigue,” “confusion,” and “vigor” of the mood state profile
(McNair and Lorr, 1964; McNair et al., 1992; Yokoyama,
2005) improved (Li et al., 2008 a, b, c; Park et al., 2010;
Lee et al., 2011; Park et al., 2011; Tsunetsugu et al.,
2013; Lee et al., 2014). Unfortunately, many people liv-
ing in cities find it difficult to access forest environments.
Thus, much attention has been focused on nature-based
stimuli, such as walking in an urban park (Song et al.,
2013), viewing rooftop forests (Matsunaga et al., 2011),
the presence of plants, including dracaena (Igarashi et al.,
2014) or roses (Ikei et al., 2014), and physical contact
with wood (Sakuragawa et al., 2008), and the relaxing ef-
fects of these stimuli have been reported.
Nature-based stimuli are intuitively perceived through
the five senses. Of these five senses, the physiological
effects of olfactory stimulation have been characterized
Physiological and psychological effects of olfactory
stimulation with D-Limonene
D. Joung
(1)
* , C. Song
(1)
**, H. Ikei**, T. Okuda**, M. Igarashi**, H. Koizumi**, B.J. Park*,
T. Yamaguchi**, M. Takagaki**, Y. Miyazaki
(2)
**
* Department of Environment and Forest Resources, Chungnam National University, 99 Daehak-ro,
Yuseong-gu, Daejeon 305-764, Republic of Korea.
** Center for Environment, Health and Field Sciences, Chiba University, 6-2-1 Kashiwanoha, Kashiwa,
Chiba 277-0882, Japan.
Key words: heart rate, heart rate variability, limonene, physiological relaxation, semantic differential method.
Abstract: Although D-Limonene can be considered an important component of nature-based stimuli, the physiological ef-
fects of olfactory stimulation with D-Limonene have not been completely claried by scientic studies. The physiological
and psychological effects of olfactory stimulation with D-Limonene were studied measuring heart rate variability (HRV),
heart rate, and subjective evaluation using a modied semantic differential method; thirteen Japanese female university
students (mean age±SD, 21.5±1.0 years) participated in the study. A concentration of 60 µL of D-Limonene was used
as olfactory stimulant and room air as control. Subjects were exposed for 90 s while sitting with eyes closed. During
D-Limonene inhalation: (1) the high-frequency (HF) value of HRV, a marker of parasympathetic nervous activity that
is enhanced in relaxing situations, was signicantly higher; (2) the heart rate was signicantly lower; and (3) subjects
reported feeling signicantly more comfortable during D-Limonene administration than control. The results obtained
clearly indicate that olfactory stimulation with D-Limonene induced physiological and psychological relaxation, provid-
ing important scientic evidence of the health benets of D-Limonene.
Adv. Hort. Sci., 2014 28(2): 90-94
(1)
These authors equally contributed to the manuscript.
(2)
Corresponding author: ymiyazaki@faculty.chiba-u.jp
Received for publication 31 March 2014
Accepted for publication 30 June 2014
91
in detail. Miyazaki et al. (1992) conducted a pioneer-
ing study which revealed that olfactory stimulation with
Chamaecyparis taiwanensis essential oil significantly
decreased blood pressure. Furthermore, inhalation of
rose oil odor was shown to suppress sympathetic nervous
activity and decrease adrenaline concentration (Haze et
al., 2002). Lavender oil has been shown to induce deep
sleep (Goel et al., 2005) and improve concentration
(Sakamoto et al., 2005).
However, evidence-based research using the indices of
autonomic nervous activity to clarify the effect of compo-
nents of these essential oils is lacking.
The essential oil components of Cryptomeria japonica
and Pinus densiflora, representative forest trees, have been
reported (Cimanga et al., 2002; Hong et al., 2004; Cheng
et al., 2009). These oils are composed of various volatile
organic compounds, including D-Limonene, α-Pinene,
β-Pinene. D-Limonene is the main component of citrus
peel oil (Bernhard, 1960; Attaway et al., 1968; Shaw,
1979; Chiralts et al., 2002; Yoo et al., 2004).
The purpose of the present study was to investigate
the physiological effect of olfactory stimulation with D-
Limonene on autonomic nervous activity by measuring its
effect on heart rate variability (HRV) (Camm et al., 1996;
Kobayashi et al., 1999) and the heart rate.
2. Materials and Methods
Subjects
Thirteen Japanese female university students (age
range, 21.5±1.0 years; mean±SD) participated in the
study. Before beginning the experiment, a full explanation
about the research aim, the experimental procedure, and
all measured indices was provided. Informed consent was
obtained from all subjects. This study was conducted in
accordance with the regulations of the Ethics Committee
of the Center for Environment, Health, and Field Sciences,
Chiba University, Japan.
Study protocol
Physiological and psychological measurements were
carried out in a chamber with an artificial climate main-
tained at 25°C with 50% relative humidity and 230-
lux illumination. D-Limonene (>95.0% purity, Tokyo
Chemical Industry Co., Ltd., Japan) was used as an ol-
factory stimulant, and room air was used as a control.
A total of 60 µL D-Limonene was injected into a 24-L
odor bag (polyethylene terephthalate film heat seal bag;
NS-KOEN Co., Ltd., Kyoto, Japan) and the odors were
presented to each subject by means of a device fitted on
the chest and situated approximately 10 cm under the
nose (Fig. 1). The flow rate of the odor was set at 3 L/
min. Subjective sensitivity to the odor was determined in
a preliminary investigation. The subjects were exposed
to the odor for 90 s while sitting with their eyes closed.
The order of presentation of D-Limonene and control
was counterbalanced.
Heart rate variability and heart rate
HRV was measured as the periods between consecutive
R waves (R-R intervals) in an electrocardiogram recorded
with a portable electrocardiograph (Activtracer AC-301A,
GMS, Japan). In this study, two major spectral compo-
nents of HRV, the low-frequency (LF; 0.04–0.15 Hz) band
and the high-frequency (HF; 0.15-0.40 Hz) band were ob-
tained by the maximum-entropy method (MemCalc/Win,
GMS, Japan). The HF power was considered to reflect
parasympathetic nervous activity, and the LF/HF power
ratio was considered to reflect the sympathetic nervous ac-
tivity (Camm et al., 1996; Kobayashi et al., 1999). Heart
rate was also investigated using R-R interval data.
Semantic differential method
The subjects provided a subjective evaluation of the
emotional impact of the odors according to a modified
semantic differential (SD) method (Osgood et al., 1957).
This method allowed the subject to assess a pair of ad-
jectives, such as “comfortable-uncomfortable,” using a
13-point scale. The SD method was performed after ad-
ministration of each odor.
Statistical analysis
All statistical analyses were performed using Statistical
Package for Social Sciences software version 20.0 (IBM
Corp., Armonk, NY, USA). A paired t-test was used to
compare differences in the physiological responses over
the 90 s of exposure to D-Limonene and air. Wilcoxon
signed-rank test was applied to analyze differences in psy-
chological response between D-Limonene and air. A one-
sided test was used in this study. In all cases, the signifi-
cance level was set at P < 0.05.
3. Results
The results of the HRV data after exposure to D-Limo-
nene and control were compared, and a significant differ-
Fig. 1 - Olfactory stimulation setup.
92
ence was found in the HF value, which is a marker of para-
sympathetic nervous activity, as shown in Figure 2. The HF
value increased 26.4% during D-Limonene administration
(827.2±191.3 ms
2
; mean±SE) compared with control (654.4
±163.6 ms
2
), indicating that parasympathetic nervous activ-
ity was significantly higher during D-Limonene administra-
tion (P<0.05). However, no significant difference was found
in the LF/HF power ratio for the two stimuli.
Figure 3 shows a comparison of the heart rate during
the administration of D-Limonene and control. Heart rate
decreased during D-Limonene administration (72.8±2.3
bpm) compared with control (74.1±2.5 bpm), and this dif-
ference was significant (P<0.05).
Figure 4 shows the results for a “comfortable” feeling
according to the subjective evaluation. Subjects reported
significantly more comfortable ratings during D-Limo-
nene administration than control (P<0.01).
4. Discussion and Conclusions
D-Limonene is one of the most common volatile or-
ganic compounds in nature (Sun, 2007). It is a major com-
ponent of various citrus oils, such as lemon, orange, grape-
fruit, and lime (Attaway et al., 1968; Bernhard, 1960;
Chiralts et al., 2002; Shaw, 1979; Yoo et al., 2004), as
well as essential oils from coniferous trees, such as Pinus
densiflora, Pinus koraiensis, Chamaecyparis obtusa, and
Cryptomeria japonica (Cimanga et al., 2002; Hong et al.,
2004; Cheng et al., 2009). In addition, because of its citrus
fragrance, D-Limonene is commonly added to perfumes,
soaps, and cosmetics (Bakkali et al., 2008).
Although D-Limonene is an important component of
nature-based stimuli, the physiological effect of olfactory
stimulation with D-Limonene has not been completely
clarified. Previously, Tsunetsugu et al. (2012) investigated
the physiological effect of olfactory simulation with D-
Limonene on blood pressure and showed that olfactory
simulation with a concentration of 10 μL D-Limonene
decreases subjects’ systolic blood pressure. However, to
our knowledge, no previous study has examined the physi-
ological effect of olfactory stimulation with D-Limonene
on HRV and heart rate.
The present study shows that olfactory stimulation with
D-Limonene induced (1) a significant increase in parasym-
pathetic nervous activities, (2) a significant decrease in the
Fig. 2 - Comparison of high-frequency power levels of heart rate vari-
ability during olfactory stimulation with D-Limonene or con-
trol (air). Data are expressed as mean ± SE; n = 13. *P < 0.05
by paired t-test.
Fig. 3 - Comparison of the heart rate during olfactory stimulation with
D-Limonene or control (air). Data are expressed as mean ± SE;
n = 13. *P < 0.05 by paired t-test.
Fig. 4 - Subjective evaluation of “comfortable” measured by a modified
semantic differential questionnaire after olfactory stimulation
with D-Limonene or control (air). Data are expressed as mean
± SE; n = 13. **P < 0.01 by Wilcoxon signed-rank test.
93
heart rate, and (3) a significant increase in a “comfortable”
feeling. These results agree with previous studies of other
nature-based stimuli (Tsunetsugu et al., 2007; Park et al.,
2008; Park et al., 2009; Park et al., 2010; Lee et al., 2011;
Park et al., 2012; Song et al., 2013; Tsunetsugu et al., 2013;
Ikei et al., 2014, Lee et al., 2014). Park et al. (2012) showed
that the HF value of HRV was significantly increased while
viewing scenery of forests using the results of field experi-
ments at 35 forests in Japan. Ikei et al. (2014) reported that
the HF component was significantly increased by viewing
roses. Song et al. (2013) revealed that parasympathetic ner-
vous activity was enhanced and the heart rate was signifi-
cantly lower after walking in an urban park than walking in
a city area. Our results support the hypothesis that olfactory
stimulation with D-Limonene has a relaxation effect that is
similar to other nature-based stimuli.
In conclusion, our results clearly indicate that olfac-
tory simulation with D-Limonene induced physiological
and psychological relaxation. And these finding provide
important scientific evidence on the health benefits of D-
Limonene exposure.
As all the participants in this study were healthy fe-
males in their twenties, further studies are needed to ascer-
tain the effect in diverse groups, including males and dif-
ferent age groups. In addition, it is necessary to examine
the effect using multiple indices, such as prefrontal cortex
activity, stress hormones, and others.
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... Previous studies on adult participants have conducted, using simultaneous measurements of brain and autonomic nervous activity in an artificial climate chamber with 2 of 13 adjustable temperature, humidity, and soundproof functions [11][12][13][14][15][16][17][18][19][20][21][22]. Regarding the physiological effects of wood-derived visual stimuli on humans, wooden wall image experiments using large-scale displays capable of presenting realistic visual stimuli have been conducted [11,12]. ...
... Studies on visual stimulation with wooden wall images have confirmed that stimulation is associated with a physiologically relaxing effect, as shown by calmed prefrontal cortex activity, increased parasympathetic nervous activity, and suppressed sympathetic nervous activity. Experiments with olfactory [13][14][15][16] and tactile stimuli [17][18][19][20][21][22] have also been conducted. The results also showed that similar to visual stimuli results, a series of physiologically relaxing effects, such as calmed prefrontal cortex activity and enhanced parasympathetic nervous activity, were heightened during relaxation, and that suppressed sympathetic nervous activity was heightened during stress. ...
... In previous laboratory experiments, various wood-derived stimuli were reported to calm prefrontal cortex activity, increase parasympathetic nervous activity (reflecting a state of relaxation), and suppress sympathetic nervous activity (reflecting a state of stress) [11][12][13][14][15][16][17][18][19][20][21][22]. Therefore, in the present study, a field experiment was performed using these physiological indices to clarify the physiological effects of the visual stimulation by a low wooden table installed in a Japanese-style room in Mokuzai Kaikan. ...
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The purpose of this study was to evaluate the physiological effects of visual stimulation by a unique Japanese low wooden table on the prefrontal cortex and autonomic nervous activities. A within-participants experiment with 26 male university students was conducted in a Japanese-style room. The visual stimuli were a low wooden table (WT) made of Japanese cypress and a low cloth-covered table (control) for an exposure time of 90 s. Near-infrared spectroscopy was used to measure the prefrontal cortex activity in the left and right prefrontal cortices as an indicator of oxyhemoglobin (oxy-Hb) concentration. Autonomic nervous activity was measured as an indicator of sympathetic (low-frequency/high-frequency component ratio, LF/HF), and parasympathetic (high-frequency components, HF) nervous activities were assessed by heart rate variability. Furthermore, the modified semantic differential method and the Profile of Mood States 2nd edition were used to measure psychological responses. Physiologically, the oxy-Hb concentration in the left prefrontal cortex and ln (LF/HF) were significantly lower during visual exposure to the WT than to the control. Psychologically, more comfortable, relaxed, and natural impressions, as well as improved mood states, were reported during visual stimulation to the WT than to the control. This study demonstrated that viewing a WT led to physiological relaxation and had a positive psychological effect on the participants.
... To verify anti-stress effects, these BVOCs have been mainly examined in animal studies with sometimes effects on psychophysiological parameters (Akutsu et al., 2002;Okano et al., 2019). Also in humans, some promising psychophysiological effects have been reported, such as lower blood pressure, lower salivary cortisol and altered brain wave patterns (Ikei et al., 2016;Jafarzadeh et al., 2013;Joung et al., 2014;J.-C. Kim et al., 2019). ...
... In rats, α-pinene could suppress stress-induced hyperthermia and thus lower physiological stress reactivity but not heart rate (Akutsu et al., 2002). Previous controlled experiments in Asian healthy individuals testing the impact of piney, woody odors via monoterpenes without stress induction revealed improved HRV: increased parasympathetic nervous activity by limonene (Joung et al., 2014) or α-pinene (Ikei et al., 2016) and declined stress index by a monoterpenes mixture (J.-C. Kim et al., 2019). ...
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Before and after Trier Social Stress Test, 91 participants (18–50 years, 67% women) inhaled one odor during 10 min: Scots pine, grass (=cis-3-hexenol), or control (=demineralized water). Group differences were tested on repeated measurements of stress (affect reports, salivary cortisol and heart rate variability) and eating behavior (food choice and craving). Both nature olfactory exposures improved some stress outcomes. Both were associated with lower cortisol in non-stress conditions, but only grass odor was more beneficial for negative affect decrease after stress. No effect on heart rate variability was seen. Some contradictory findings were present for eating behavior. In non-stress situations, grass odor increased vegetable preference, while the pine odor group had higher sweet high-fat snack preference. Grass odor was also reported to induce healthier food choices. During stress recovery, both pine and grass odor groups had higher preference to sweet high-fat snacks.
... Additionally, BOVCs has direct benefits for human health. Inhaling BVOCs like limonene and pinene can result in antioxidant and anti-inflammatory effects on the airways, and the pharmacological activity of some terpenes absorbed through inhalation may be also beneficial to promote brain functions by decreasing mental fatigue, inducing relaxation, and improving cognitive performance and mood (Joung et al., 2015;Antonelli et al., 2020). However, the presence of some harmful components such as paraxylene, dichloromethane, and trichloromethane has also been detected in some plant BVOCs (Ronald, 1997;Li et al., 2022). ...
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Plant biogenic volatile organic compounds (BVOCs) possess ecological functions in antimicrobial benefits and air purification. The objectives of the study were to determine the differences in antimicrobial capacity of bamboo forests at different sampling sites. Three common bamboo species—Phyllostachys edulis, Bambusa emeiensis, and Phyllostachys violascens—were selected to determinate the antimicrobial activity of bamboo forests as well as under ex vivo conditions. Natural sedimentation method was used to determine the microbe counts in bamboo forests, and the microbe counts in grassland in the same area was measured as control treatment. The results showed that except for the P. violascens in Ya’an, the airborne microbial content of the sampling sites in bamboo forests was significantly lower relative to that of grassland in the same area, and inhibition rate reached 74.14% in the P. violascens forest in Dujiangyan. P. edulis forest and P. violascens forest in Ya'an had significantly lower inhibition rates than the other sampling sites, and there was no significant difference in the inhibition rates among the rest of the bamboo forest. The bacterial inhibition rate of bamboo leaves under ex vivo conditions varied with bamboo species and bacterial strains, with higher antibacterial activity against Gram-negative bacteria overall. Escherichia coli was sensitive to B. emeiensis leaves, while Staphylococcus aureus and Bacillus subtilis were sensitive to P. violascens leaves. Moreover, Candida albicans, S. cremoris, and Shigella Castellani were sensitive to P. edulis leaves. An analysis of the BVOCs composition from P. edulis collected in Changning by SPME-GC/MS revealed that the relative content of ocimene was obviously higher than other components. This study showed that P. edulis BVOCs have strong inhibitory ability to the tested microorganisms, and its main constituent, ocimene, has health benefit. P. edulis has the potential to become a forest recreation bamboo species.
... However, the lack of research on human subjects makes it difficult to discuss physiological background concerning the results of psychophysiological studies such as the present study. On the other hand, one study on olfactory stimulation with limonene demonstrated enhanced HF and significantly lower HR in relaxing situations [56], providing some insights into the physiological effects of limonene. These effects may lead to the current study findings. ...
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... Woody smell is known to act as a mood relaxant 26 , and α-pinene, β-pinene, and d-limonene are typical aromatic components of wood or wood-derived interior materials. Inhalation of d-limonene has been shown to enhance parasympathetic nervous activity, decrease heart rate, and provide 'comfortable' stimulation 27 . The essential oils containing these aroma compounds are widely used in aroma therapy, a holistic healing treatment that uses natural plant extracts to promote health and well-being. ...
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Recent studies have shown that some people claim that their skin gases provoke allergy-like reactions in people in their near vicinity. Such a phenomenon or symptom is called ‘people allergic to me (PATM)’. Although numerous people suffer from PATM, the actual conditions are unknown. The aim of this study was to investigate the characteristics of human skin profiles in patients with PATM by measuring the dermal emission fluxes of 75 skin gases using passive flux sampler and gas chromatography/mass spectrometry. We found common features in the human skin gas profiles of 20 subjects with PATM, with a significant difference from those of 24 non-PATM subjects: greater emissions of petrochemicals, organosulfur compounds, and some aldehydes and lower emissions of aroma compounds and others. The ratio of toluene to benzaldehyde is considered a vital sign that suggests the fundamental of PATM. These findings indicate that PATM is a medically unexplained phenomenon or symptom worthy of further research, which requires an interdisciplinary approach.
... In field experiments, walking or viewing the surroundings in a forest or park has previously been shown to calm brain activity (Park et al., 2007;Song et al., 2020); increase parasympathetic nervous activity, which increases during relaxation (Kobayashi et al., 2015(Kobayashi et al., , 2018Song et al., 2019a,b); decrease sympathetic nervous activity, which increases during stress (Kobayashi et al., 2015(Kobayashi et al., , 2018Song et al., 2019a,b); and decrease stress hormone (cortisol) levels (Park et al., 2010;Kobayashi et al., 2017). In laboratory experiments, viewing flowers or foliage plants, smelling flowers or natural essential oils, listening to the sound of a babbling brook, and touching wooden plates have been shown to calm brain activity (visual stimuli: Song et al., 2017Song et al., , 2018Nakamura et al., 2019;olfactory stimuli: Igarashi et al., 2014b;Ikei et al., 2015a,b;auditory stimuli: Jo et al., 2019;tactile stimuli: Ikei et al., 2017atactile stimuli: Ikei et al., ,b, 2018atactile stimuli: Ikei et al., ,b, 2019; increase parasympathetic nervous activity, which increases during relaxation (visual stimuli: Ikei et al., 2013Ikei et al., , 2014aIkei et al., ,b, 2020Komatsu et al., 2013;Jo et al., 2022;olfactory stimuli: Igarashi et al., 2014a;Ikei et al., 2015aIkei et al., , 2016Joung et al., 2014;tactile stimuli: Ikei et al., 2017atactile stimuli: Ikei et al., ,b, 2018atactile stimuli: Ikei et al., ,b, 2019; and decrease sympathetic nervous activity, which increases during stress (visual stimuli: Ikei et al., 2013Ikei et al., , 2014bIgarashi et al., 2015, auditory stimuli: Jo et al., 2019tactile stimuli: Ikei et al., 2018btactile stimuli: Ikei et al., , 2019. As mentioned above, exposure to various types of nature has been shown to have a physiologically relaxing effect on subjects. ...
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This study investigated the effects of wood-derived visual and olfactory stimuli on subjective evaluations during work and rest. Twelve participants experienced seven conditions involving walnut panel interiors, Hinoki cypress scents, or their combination, introduced during either work or rest phases. A within-subjects design was used to assess spatial impressions, mood states, and fatigue. Visual stimuli significantly improved visual impressions across items such as “settling–unsettling” and “luxurious–simple” (p < 0.05). The Hinoki scent enhanced olfactory impressions and, when introduced during rest, reduced negative mood states including “Anger–Hostility” and “Confusion–Bewilderment” (p < 0.05). Combined stimuli further improved scent impressions (p < 0.1), suggesting cross-modal effects. However, their introduction during work increased “Anger–Hostility” (p < 0.05), highlighting the importance of context. Although the within-subjects design supports internal validity, the small sample size (n = 12) limits generalizability. These findings provide insight into the context-sensitive use of wood-derived sensory elements in workplace design.
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. Despite increasing attention toward forest therapy as an alternative medicine, very little evidence continues to be available on its therapeutic effects. Therefore, this study was focused on elucidating the health benefits of forest walking on cardiovascular reactivity. Methods . Within-group comparisons were used to examine the cardiovascular responses to walking in forest and urban environments. Forty-eight young adult males participated in the two-day field research. Changes in heart rate variability, heart rate, and blood pressure were measured to understand cardiovascular reactivity. Four different questionnaires were used to investigate the changes in psychological states after walking activities. Results . Forest walking significantly increased the values of ln(HF) and significantly decreased the values of ln(LF/HF) compared with the urban walking. Heart rate during forest walking was significantly lower than that in the control. Questionnaire results showed that negative mood states and anxiety levels decreased significantly by forest walking compared with urban walking. Conclusion . Walking in the forest environment may promote cardiovascular relaxation by facilitating the parasympathetic nervous system and by suppressing the sympathetic nervous system. In addition, forest therapy may be effective for reducing negative psychological symptoms.
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In recent years, the physiological relaxing effect brought by nature is becoming clear; however, many workers find it difficult to be exposed to nature in their working environment. Exposure to fresh flowers represents an opportunity to incorporate nature into their working lives. In this study, we examined the effects of exposure to roses on physiological and psychological variables (heart rate variability, pulse rate, and subjective responses) in office workers. The experimental site was Mizuho Information & Research Institute, Inc., in the Tokyo metropolitan area. Thirty-one male office workers were included in the present study. The subjects were exposed to thirty unscented pink roses (Rosa, Dekora) arranged in a cylindrical glass vase for 4 min. In the control condition, the subjects were not exposed to flowers. After the experiments, the subjects completed a questionnaire. The order of exposure was counterbalanced among subjects. Among subjects exposed to roses, the high-frequency component of heart rate variability was significantly higher than in controls. Similarly, 'comfortable,' 'relaxed' and 'natural' feelings were more common in subjects exposed to roses. Data from this study support the presence of physiological and psychological relaxing effects of being exposed to flowers on office workers.
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Natural scenes like forests and flowers evoke neurophysiological responses that can suppress anxiety and relieve stress. We examined whether images of natural objects can elicit neural responses similar to those evoked by real objects by comparing the activation of the prefrontal cortex during presentation of real foliage plants with a projected image of the same foliage plants. Oxy-hemoglobin concentrations in the prefrontal cortex were measured using time-resolved near-infrared spectroscopy while the subjects viewed the real plants or a projected image of the same plants. Compared with a projected image of foliage plants, viewing the actual foliage plants significantly increased oxy-hemoglobin concentrations in the prefrontal cortex. However, using the modified semantic differential method, subjective emotional response ratings ("comfortable vs. uncomfortable" and "relaxed vs. awakening") were similar for both stimuli. The frontal cortex responded differently to presentation of actual plants compared with images of these plants even when the subjective emotional response was similar. These results may help explain the physical and mental health benefits of urban, domestic, and workplace foliage.
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Interaction with nature has a relaxing effect on humans. Increasing attention has been focused on the therapeutic effects of urban green space; however, there is a lack of evidence-based field research. This study provided scientific evidence supporting the physiological and psychological effects of walking on young males in urban parks in winter. Subjects (13 males aged 22.5 +/- 3.1 years) were instructed to walk predetermined 15-minute courses in an urban park (test) and in the city area (control). Heart rate and heart rate variability (HRV) were measured to assess physiological responses. The semantic differential (SD) method, Profile of Mood States (POMS), and State-Trait Anxiety Inventory (STAI) were used to determine psychological responses.Heart rate was significantly lower and the natural logarithm of the high frequency component of HRV was significantly higher when walking through the urban park than through the city area. The results of three questionnaires indicated that walking in the urban park improved mood and decreased negative feelings and anxiety. Physiological and psychological data from this field experiment provide important scientific evidence regarding the health benefits of walking in an urban park. The results support the premise that walking in an urban park has relaxing effects even in winter.
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It is widely believed that coming into contact with forest environments is somehow beneficial to human well-being and comfort. In Japan, "Shinrin-yoku" (taking in the atmosphere of a forest) has been proposed to be a relaxation activity associated with forest recreation. The purpose of this study was to examine the physiological effects of forest recreation on the autonomic nervous activity. The subjects were twelve male university students (21.8 ± 0.8 years old). On the first day of the experiment, six subjects were sent to a forest area, and the other six to a city area. On the second day, each subject was sent to the area he did not visit on the first day as a cross check. The subjects walked (15 minutes) around their assigned areas before noon, and sat on chairs viewing (15 minutes) the landscapes of their assigned areas in the afternoon. Heart rate variability (HRV), blood pressure, and pulse rate were measured as physiological indices. Measurements were taken at the place of accommodation in the morning, before and after walking, and before and after viewing at their assigned field areas. Pulse rate, diastolic blood pressure and LF/(LF+HF) (LF- low frequency, HF- high frequency) components of HRV were significantly lower in the forest area than in the city area. HF components of HRV tended to be higher in the forest than in the city. In conclusion, the results of the physiological measurements show that forest recreation enabled effective relaxation in people, both of the mind and body.
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The purpose of this chapter is to clarify the physiological relaxation effect of a forest environment using field tests. We conducted field experiments in 35 forests across Japan. The subjects were twelve male university students at each location (420 in total; age range 21.8 ± 1.6 years). On the first day, 6 subjects were sent to a forest area, and the others to a city area. On the second day, each group was sent to the other area. The subjects walked (for 16 ± 5 min) around their assigned areas, and sat on chairs viewing the landscapes of their assigned areas (for 14 ± 2 min). Salivary cortisol, blood pressure, pulse rate, and heart rate variability (HRV) were used as indices. Measurements were taken at the place of accommodation in the morning, before and after walking, and before and after viewing at their assigned field areas. The R-R interval was also measured during the walking and viewing periods. The results show that forest environments promote lower concentrations of cortisol, lower pulse rate, lower blood pressure, greater parasympathetic nerve activity, and lower sympathetic nerve activity than city environments. These results will contribute to the development of a research field dedicated to forest-based therapy.
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The present study investigated the physiological and psychological effects of viewing urban forest landscapes on 48 young male urban residents. Four forested areas and four urban areas located in central and western Japan were used as the test sites. We found that in the forested areas, the subjects exhibited (i) significantly lower diastolic blood pressure, (ii) significantly higher parasympathetic nervous activity, but significantly lower sympathetic nervous activity, and (iii) significantly lower heart rate. The forest landscapes (iv) obtained better scores in subjective ratings, and (v) induced significantly less negative and more vigorous moods. Taken as whole, these findings suggest that even a short-term viewing of forests has relaxing effects. We have thus concluded that the approach taken in this study is useful in exploring the influences of urban green space on humans, as well as contributing to the planning and design of a healthy environment for urban residents.