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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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... The difference between forest and urban environments can often lead to stress in people [10]. Therefore, humans feel comfortable when visiting forests [11][12][13] and contacting with various resources derived from forests [14][15][16][17]. "Forest healing" is an attempt to induce stress relief, mental and physical relaxation, and link health promotion with immunity improvement by utilizing these mechanisms. ...
... Many studies have been performed on cypress that emits a large amount of phytoncide. Studies using leaf-extracted oil, wood-extracted oil, and wood chips have shown positive effects on physiological and psychological relaxation and the improvement of immune function [15][16][17]. However, verification of the effectiveness of other tree species is insufficient. ...
... In addition, most studies on olfactory stimulation of forest-derived substances reported effects in female [15][16][17], and there is a lack of research on the physiological effects in males, on which more data are needed. This study also examined the differences in the physiological and psychological effects of fir essential oil inhalation between male and female university students. ...
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Numerous studies have reported a significant increase in stress experienced by students owing to the COVID-19 pandemic. Recently, interest in stress management using nature-derived substances has increased. However, studies examining the effects of olfactory stimulation by fir are lacking. The aim of this study was to investigate the physiological and psychological effects of inhaling fir essential oil. Additionally, differences between male and female participants were compared. Twenty-six university students (16 female and 10 male students; mean age, 21.5 ± 1.9 years) participated in this study. Fir essential oil was used for olfactory stimulation, with normal room air as the control. The odor was administered for 3 min. Heart rate variability and heart rate were used as indicators of autonomic nervous system activity. The Profile of Mood States and State-Trait Anxiety Inventory were used as psychological indicators. The ln(Low Frequency/High Frequency) ratio, which is an indicator of sympathetic nervous activity reflecting a stressful or aroused state during stimulation with fir essential oil, was significantly lower than during the control condition. Assessment of psychological indicators showed that the positive mood of “vigor” improved significantly and negative moods of “tension–anxiety”, “depression”, “anger–hostility”, “fatigue” and anxiety levels reduced significantly after inhaling fir essential oil compared to the control condition. This study showed that inhalation of fir essential oil has physiologically and psychologically relaxing effects, with differences in results depending on the sex of the participants.
... A number of previous studies have reported the positive benefits of forest therapy on mental health. For example, forest therapy has been reported to reduce psychological stress or mental fatigue [30], anxiety [31,32], and improve mood [33,34], as well as improve quality of life [35,36]. ...
... Previous studies used indicators evaluating the variables of the depression area among detailed items such as the Profile of Mood States [31,34,45], Stress Response Inventory [46], Multiple Mood State [47], and the Depression Anxiety and Stress Scale [48], rather than objectified evaluation indicators to determine symptoms of depression patients. In addition, most of the studies reported so far have been performed in dense forests far from the city [30][31][32][33][34][35][36]. Such forests have beautiful natural scenery but lack accessibility, so they can not only be limited to use by depression patients but also have sustainability problems. ...
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Depression is a common serious mental health condition that can have negative personal and social consequences, and managing it is critical for treating depression patients. Forest therapy is emerging as a promising non-pharmacological intervention to improve mental health. However, although the effectiveness of forest therapy programs using forests far from the city has been proven, it is not well known that urban forests can be easily accessed in daily life. Therefore, this study aimed to examine the effects of an urban forest therapy program on depression symptoms, sleep quality, and somatization symptoms of depression patients. To evaluate this, a randomized controlled trial (RCT) design was employed. A total of 47 depression patients participated in this study (22 in the urban forest therapy program group and 25 in the control group). The Beck Depression Inventory (BDI), the Hamilton Rating Scale for Depression (HRSD), the Pittsburgh Sleep Quality Index (PSQI), and the Patient Health Questionnaire-15 (PHQ-15) were administered to each participant to assess the effects of the urban forest therapy program. The results of this study revealed that depression patients in the urban forest therapy program had significantly alleviated depression symptoms and improved sleep quality and somatization symptoms compared to the control group. In conclusion, this study demonstrates the possibility that the urban forest therapy program could be used as an effective non-pharmacological treatment to alleviate depression disorder.
... In addition, many studies have shown that natural environments such as forests positively affect mood states [37][38][39]. For example, Pretty et al. [37] reported that the participants' mood and self-esteem improved considerably after the forest exercise. ...
... For example, Pretty et al. [37] reported that the participants' mood and self-esteem improved considerably after the forest exercise. Joung et al. [38] investigated physiological and psychological reactions using near-infrared spectroscopy. ...
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This systematic review and meta-analysis aimed to summarize the effects of forest therapy on depression and anxiety using data obtained from randomized controlled trials (RCTs) and quasi-experimental studies. We searched SCOPUS, PubMed, MEDLINE(EBSCO), Web of science, Embase, Korean Studies Information Service System, Research Information Sharing Service, and DBpia to identify relevant studies published from January 1990 to December 2020 and identified 20 relevant studies for the synthesis. The methodological quality of eligible primary studies was assessed by ROB 2.0 and ROBINS-I. Most primary studies were conducted in the Republic of Korea except for one study in Poland. Overall, forest therapy significantly improved depression (Hedges’s g = 1.133; 95% confidence interval (CI): −1.491 to −0.775) and anxiety (Hedges’s g = 1.715; 95% CI: −2.519 to −0.912). The quality assessment resulted in five RCTs that raised potential concerns in three and high risk in two. Fifteen quasi-experimental studies raised high for nine quasi-experimental studies and moderate for six studies. In conclusion, forest therapy is preventive management and non-pharmacologic treatment to improve depression and anxiety. However, the included studies lacked methodological rigor and required more comprehensive geographic application. Future research needs to determine optimal forest characteristics and systematic activities that can maximize the improvement of depression and anxiety.
... However, urban planning decision-makers are limited in obtaining different positive sensory stimuli through natural planning to improve biodiversity by the difficulty of quantifying nature outside of vision [42]. When the stimuli of smell [43,44], hearing [45], and touch [46,47] are presented alone, the psychological effects differ. Therefore, this study focuses on the exploration of the visual stimulation of the landscape to explore the restoration and aesthetic differences of urban forests based on one-way visual senses of various spatial elements. ...
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City green space can promote people’s health and aesthetic satisfaction; however, most extant research focuses on suburban forests and urban parks. Urban landscape forests have important ecological and aesthetic value for urban environments. This study conducted a visual stimulation to examine the impact of four common spatial element combinations in urban landscape forests on teenagers’ recovery potential and preference. The results indicate that urban landscape forests had positive physiological and psychological effects on adolescents, including decreased blood pressure, improved heart rate, reduced anxiety, and improved recovery ability. Diastolic blood pressure relief performance was better among males than females. In addition, a stepwise linear regression analysis was performed to explore the quantitative relationship between spatial elements and recovery and preference values. The results demonstrate that water elements were a significant predictor in the quantitative relationship between spatial elements in landscape forests and restoration and preference values. Terrain, flower, and shrub elements did not have a significant effect on overall restoration and preference values. This study highlights the intervention value of urban landscape forests in promoting the health and well-being of adolescents, with implications for future planning and design of urban landscape forests.
... The forest environments consist of scenery, scent, sounds, phytoncides, anions, sunlight, microclimate environments, and topography. These elements act as therapeutic factors by stimulating the five senses [1,17,28,[44][45][46][47], promoting psychological and physiological relaxation [25][26][27][28][29][30]48], supporting cognitive recovery [49], providing beneficial chemicals to the human body [50][51][52][53][54][55][56][57], and giving a recreational space [33,58]. ...
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In recent decades, forests have expanded from natural resources for conservation and production to health-promoting resources. With the growing body of evidence supporting the therapeutic effects of forests, the number of investigations on the relationship between forest characteristics and therapeutic effects have increased. However, quantitative synthesis of primary studies has rarely been conducted due to a limited number of health studies including forest description and high heterogeneity of forest variables. In this study, we conducted a systematic review and meta-analysis to evaluate the relationship between the forest structure and the therapeutic effect. We systematically searched the studies examining the therapeutic effects of forests with different stand density and canopy density and synthesized the results. As a result of subgroup analysis, we found that stand density modifies the therapeutic effects. Emotional and cognitive restoration showed greatest improvement in low-density forests with a stand density of less than 500/ha and the therapeutic effects diminish as the stand density increases. The impact of canopy density was not found due to a lack of studies reporting canopy density. Although some limitations remain, the findings in this study have great significance in providing the basis for establishing management strategies of forests for therapeutic use.
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The demand for wood has increased in recent years due to new technical possibilities and environmental concerns. This paper provides an analysis of the factors that affect the use of wood in the construction sector, and an assessment of their importance in individual countries and for groups of stakeholders. The study covers the technical, societal, political, economic, and gender aspects of wood construction, with the aim of increasing global understanding regarding national differences, the current situation, and the potential for further development. The subject was investigated using a survey, and the most important opportunities for and barriers to growth in the use of wood in the construction sector were selected, following a statistical analysis. The results indicate strong regional and cultural differences regarding the acceptance of some of the opportunities and barriers related to the development of wood construction. The findings indicate that there is a need to promote wood construction based on its technical and economic benefits rather than its societal ones. On the other hand, the current societal barriers should be addressed as a priority, together with the establishment of common and harmonized policies. The results of this study, therefore, will contribute to the generation of regional-sensitive information that can be useful for policymakers when updating the building codes in their individual countries.
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We document the species richness and volatile oil diversity in Sonoran Desert plants found in the Arizona Uplands subdivision of this binational USA/Mexico region. Using floristics, we determined that more than 60 species of 178 native plants in the ancient ironwood-giant cactus forests emit fragrant biogenic volatile organic compounds (BVOCs), especially with the onset of summer monsoons. From these desert species, more than 115 volatile oils have been identified from one biogeographic region. For the 5 BVOCs most commonly associated with “forest bathing” practices in Asian temperate forests, at least 15 Sonoran Desert plant species emit them in Arizona Uplands vegetation. We document the potential health benefits attributed to each of 13 BVOCs in isolation, but we also hypothesize that the entire “suite” of BVOCs emitted from a diversity of desert plants during the monsoons may function synergistically to generate additional health benefits. Regular exposure to these BVOC health benefits may become more important to prevent or mitigate diseases of oxidative stress and other climate maladies in a hotter, drier world.
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In the present study, we examined the modulatory effects of Melia azedarach Linn flowers on human physiological and psychological behaviors. Inhalation of fresh flowers for 20 min decreased salivary amylase activity. Electroencephalogram analysis exhibit that inhalation of fresh flowers reduced alpha brainwave, while gamma, delta, and theta-brainwaves were increased. Moreover, systolic blood pressure (SBP), diastolic blood pressure (DBP), and heart rate (HR) were decreased after inhalation of flowers. Furthermore, inhalation of flowers reduced sympathetic nervous system (SNS) activity and increased parasympathetic nervous system (PSNS) activity. In addition, we extracted volatiles from the flowers by the solid-phase micro-extraction (SPME) method and the chemical composition was determined by mass spectrometry. Fifteen compounds were identified, among them benzaldehyde (68.50 %) and phenylacetaldehyde (22.26 %) were the major compounds. Similarly, inhalation of 0.25 % benzaldehyde or phenylacetaldehyde reduced SBP, DBP, HR, and SNS activity, whereas PSNS was increased. Furthermore, the profile of mood states (POMS) scores support that inhalation of fresh flowers significantly reduced depression, confusion, and tension. Anger, fatigue, and vigor were also decreased. These results suggest that M. azedarach flowers or their major compounds can be novel modulators of SNS dysfunction as well as aromatherapy.
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This study aimed to demonstrate the effects of forest-derived visual, auditory, and combined stimulation on brain activity, autonomic nervous system activity, and subjective spatial impressions. The participants included 20 Japanese female university students (age 22.1 ± 1.8 years). Each participant viewed a gray image for 60 s with no sound (rest period), followed by an image of a forest scene with no sound (visual stimulation), a gray image with forest sounds (auditory stimulation), an image of a forest scene with forest sounds (combined stimulation), and a gray image with no sound (control) for 90 s. As indicators, near-infrared spectroscopy, heart rate variability measurement, heart rate monitoring, and modified semantic differential method were used. Compared to the control condition, combined stimulation significantly decreased oxyhemoglobin (oxy-Hb) concentrations in both prefrontal cortices and increased parasympathetic nervous activity, reflecting a relaxed state; visual and auditory stimulation significantly decreased the oxy-Hb concentration in the right prefrontal cortex; and “comfortable,” “relaxed,” “natural,” and “realistic” feelings increased significantly for all stimulations. In conclusion, forest-derived visual, auditory, and combined stimuli induced physiologically and psychologically relaxing effects, and physiological relaxation was more pronounced under combined stimulus.
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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.