Joy and Calm: How an Evolutionary Functional Model of Affect Regulation Informs Positive Emotions in Nature

Abstract

Key theories of the human need for nature take an evolutionary perspective, and many of the mental well-being benefits of nature relate to positive affect. As affect has a physiological basis, it is important to consider these benefits alongside regulatory processes. However, research into nature and positive affect tends not to consider affect regulation and the neurophysiology of emotion. This brief systematic review and meta-analysis presents evidence to support the use of an existing evolutionary functional model of affect regulation (the three circle model of emotion) that provides a tripartite framework in which to consider the mental well-being benefits of nature and to guide nature-based well-being interventions. The model outlines drive, contentment and threat dimensions of affect regulation based on a review of the emotion regulation literature. The model has been used previously for understanding mental well-being, delivering successful mental health-care interventions and providing directions for future research. Finally, the three circle model is easily understood in the context of our everyday lives, providing an accessible physiological-based narrative to help explain the benefits of nature.

Full text

THEORETICAL ARTICLE
Joy and Calm: How an Evolutionary Functional Model of Affect
Regulation Informs Positive Emotions in Nature
Miles Richardson
1
&Kirsten McEwan
2
&Frances Maratos
1
&David Sheffield
1
#Springer International Publishing 2016
Abstract Key theories of the human need for nature take an
evolutionary perspective, and many of the mental well-being
benefits of nature relate to positive affect. As affect has a
physiological basis, it is important to consider these benefits
alongside regulatory processes. However, research into nature
and positive affect tends not to consider affect regulation and
the neurophysiology of emotion. This brief systematic review
and meta-analysis presents evidence to support the use of an
existing evolutionary functional model of affect regulation
(the three circle model of emotion) that provides a tripartite
framework in which to consider the mental well-being bene-
fits of nature and to guide nature-based well-being interven-
tions. The model outlines drive, contentment and threat di-
mensions of affect regulation based on a review of the emotion
regulation literature. The model has been used previously for
understanding mental well-being, delivering successful men-
tal health-care interventions and providing directions for fu-
ture research. Finally, the three circle model is easily under-
stood in the context of our everyday lives, providing an acces-
sible physiological-based narrative to help explain the benefits
of nature.
Keywords Affect regulation .Positive affect .
Neurophysiology of emotion .Nature .Well -bei ng
Biophilia takes an evolutionary perspective that humans have
a biologically based innate need to affiliate with life in the
natural world and to recognise and seek out the resources
the natural world provides (e.g. food, water, shelter) (Wilson
1984; Kellert 1993). The human brain is also a product of
evolution, and difficulties including mental health can arise
when we become ignorant of our origins as part of nature
(Wilson 1992). Following the functional-evolutionary per-
spective of Ulrich (1983), affective emotions are often consid-
ered in research concerning our connection to nature, and the
benefits people derive from nature. Such work often focusses
on positive affect (e.g. McMahan and Estes 2015) but does not
tend to consider an evolutionary functional view of affect
regulation and the neurophysiology of emotion. As our con-
nection to and the benefits of nature are affective, and affect
has a physiological basis, it is important to consider the well-
being benefits of nature within a model of affect regulation.
This review considers the emotion regulation literature before
presenting evidence from empirical work in natural environ-
ments to support the application of an existing evolutionary
functional model of affect regulation, namely the three circle
model of emotion (Gilbert 2005), to this domain. This model
provides a useful framework in which to consider positive
affect and the mental well-being benefits of nature.
Neurophysiology of Emotion
Affect is the constant companion of sensation, with feelings,
rather than thoughts, coming first when encountering nature;
Ulrich’s functional-evolutionary perspective suggests that en-
counters with nature can induce wakeful relaxation and posi-
tive emotional reactions (Ulrich 1983). Emotions provide the
impetus for action and motivation, impacting the body in a
manner that cognition alone cannot (Gilbert 2014). Emotions
have a biological basis and analysis of emotion should not
exclude regulatory processes; emotions and their regulation
*Miles Richardson
m.richardson@derby.ac.uk
1
University of Derby, Kedleston Road, Derby DE22 1GB, UK
2
Cardiff University, Heath Park, Cardiff CF14 4YS, UK
Evolutionary Psychological Science
DOI 10.1007/s40806-016-0065-5

should be considered as one (Kappas 2011). For well-being,
these emotions need to be balanced as affect regulation sys-
tems control our heart and muscles and the way our brain
functions in order to achieve balance (Kappas 2011).
Taking an evolutionary perspective, origins of the scientific
approach to emotion are largely credited to Darwin (1872)and
the idea that emotions have evolved as solutions to nature that
promote survival. Termed ‘serviceable association habits’,
Darwin suggested that emotions and their expressions
evolved because they are reliable antecedents of particular
behaviours, with Frijda (1987) suggesting a relatively small
set of such action tendencies. According to Frijda, these action
tendencies allow us to establish, maintain or disrupt a relation-
ship with the environment. This is perhaps not too dissimilar
to the arguments of Gray (1982) who suggested that three
fundamental emotion systems exist in the brain to enable
situation-specific responses (primarily to resolve anxiety): a
fight or flight system (F/FLS), a behavioural activation system
(BAS) and a behavioural inhibition system (BIS). Based upon
research in rats, Gray suggested a number of brain circuits and
roles involved in these different systems. Albeit simplified, the
F/FLS system (amygdala, hypothalamus, central grey) serves
to enable defensive reactions, the BAS (basal ganglia, dopa-
minergic tracts) to enable approach to signals of reward and
non-punishment and the BIS (septo-hippocampal circuits) can
be thought of as a mediator when conflict arises in situations
of approach-avoidance conflict. At the level of the rat, the
latter could be considered conflict between the presence of
food (appetitive and rewarding) and the scent of a cat (preda-
tory and feared).
Of note, much research has focused on the F/FLS system
drawing, for example, from the early work of Papez (1937)
and MacLean (1949). Emerging from such literature, great
emphasis has been given to the limbic system and regions
such as the amygdala in emotion and threat processing.
Largely based upon the research of LeDoux (1998,2014),
the amygdala is well-established as playing a key role in the
processing of emotional information, regulating emotional re-
sponses and controlling fear reactions in a range of species
(see for example Fox et al. 2015; Phelps and Ledoux 2005 for
reviews). Indeed, much recent research still supports the no-
tion that a phylogenetically old subcortical pathway provides
rapid, but coarse, threat-related signals in humans via the
amygdala (Méndez-Bértolo et al. 2016; Maratos et al. 2009).
However, this approach is not without criticism, and Pessoa
(2014) suggests that given its rich connectivity, the amygdala
is arguably a processing hub belonging to a minimum of at
least three networks pertaining to visual processing, autonom-
ic awareness and the generation of bodily states, and a values
network in which the value of a current state and future reward
is evaluated relatively. This values network arguably arises
given the rich connectivity between the amygdala and almost
all regions of the prefrontal cortex (PFC) (Averbeck and Seo
2008). Certainly, the PFC (commonly referred to as the ‘seat
of reasoning’) is now well-established in emotion regulation
processes (see Ochsner et al. 2012 for review), with disrupted
connectivity between limbic and prefrontal brain regions im-
plicated in a number of affective disorders such as anxiety
(Etkin 2009) and depression (de Almeida et al. 2009).
A different, but no less valid, perspective to approach
emotion and emotion regulation is via identification of the
neurochemical systems that influence emotional responding.
Here, prominence should be given to Panksepp (1998a,b)
whose research gave rise to the importance of different neu-
rotransmitters for particular affective systems/states. Again
applying a tripartite model or the notion of a ‘triune’brain
(MacLean 1990), Panksepp proposed that affective processes
can be divided into reflective affects such as pain or pleasure
(brain stem regions), grade A emotions such as fear or joy
(mid brain regions) and higher sentiments such as shame,
guilt, empathy, etc. (frontal cortex). Importantly, however,
Panksepp noted that all such emotions were subserved by a
number of neurotransmitters—from serotonin and noradrena-
line (norepinephrine) more generally across all levels, to do-
pamine, oxytocin and opioids more specifically involved in
seeking, reward, play/pleasure and care.
For example, dopamine is key in reward processes
(Bressan and Crippa 2005), with dopamine-producing neu-
rons in the substantia nigra connecting to the basal ganglia.
In a second pathway, dopamine-producing neurons in the ven-
tral tegmental area (VTA) connect with the hypothalamus and
basal ganglia (collectively named the ‘pleasure centre’by
Olds 1956), as well as the amygdala and frontal regions.
Oxytocin has been suggested to be key in maternal care and
romantic care, with receptors for oxytocin, located in high
numbers, for example, in the central nucleus of the amygdala.
Additionally, in rats, blocking receptors for oxytocin in the
VTA leads to the blocking of maternal behaviours (Pedersen
et al. 1994), and in prairie voles, the blocking of oxytocin
leads to decreased pair bonding and increased promiscuity
(Cho et al. 1999). Human research also appears to demonstrate
the central role of oxytocin in affiliative relationships span-
ning kin, romantic bonding and trust (Graustella and
MacLeod 2012), but this research is not without its critics
(Nave et al. 2015). Finally, opioids are well-established in
the relief of pain, with research suggesting that both opioid
and dopamine systems are important in modulating both pain
and pleasure (Leknes and Tracey 2008).
Gilbert (2005,2014) attempted to assimilate such research
from these varied approaches to emotion regulation into an
accessible model. It is of note that whilst this is not the only
recent model of emotion regulation (see for example Etkin
et al. 2015; Lindquist et al. 2012), the approach taken by
Gilbert is to draw literature from beyond the neuroimaging
literature as well as place greater emphasis on positive emo-
tions in any such model. In doing so, Gilbert (2014) outlines a
Evolutionary Psychological Science

‘three circle model of emotion’and affect regulation (see
Fig. 1). This model not only draws from existing theory and
literature such as that above, but also takes into account ad-
vances made with regard to our understanding of affiliative
and positive emotions with respect to reward pathways, dopa-
mine and oxytocin (see also Depue and Morrone-Strupinsky
2005 for review), as well as research into the balance between
the sympathetic and parasympathetic nervous system by
Porges (1995,2007,2009). The three circles of this model
represent drive, threat and contentment and are easily under-
stood in the context of our everyday lives. Drive—resource
focus, wanting, pursuing, achieving and consuming—is asso-
ciated with feelings of excitement, joy and pleasure and nota-
bly linked to dopaminergic systems. The function of this sys-
tem is to drive us towards resources and rewards.
Contentment—safeness, connection and affiliative focus—is
associated with feelings of contentment, safeness, calm and
notably linked to oxytocin and opiate systems. The function of
this system is to ‘turn-off or tone-down’drive and threat sys-
tems and to restore energy. This system also evolved to enable
attachment and functions to provide a calming soothing pro-
cess when affiliative signals are present so that individuals can
engage with affiliation and attachment behaviours. Threat—
anxiety focus, protection, safety seeking, activating and
inhibiting—is associated with feelings of anxiety, anger and
sadness and notably linked to adrenaline, as well as cortisol
and also noradrenaline. The function of this system is defen-
sive and protective, to keep us alert to threats and to seek
safety.
When considering responses to natural environments,
Ulrich (1983) noted that drive and contentment can be seen
to correspond with positive and relaxing reactions. From such
a perspective, the balance between drive and contentment can
also be compared to the long-standing account of two phases
of positive states: appetitive activity ‘doing’and consumma-
tory response ‘being’(Tinbergen 1951). Once a goal has been
achieved (e.g. a resource such as food has been obtained),
drive systems need to be ‘turned off or toned down’(down-
regulated) to balance energy expenditure and provide positive
affect in the form of contentment. This is not dissimilar to the
approach of Gray (1982), but in the nature example described
here, the contentment system is seen as affect-regulating
(Depue and Morrone-Strupinsky 2005) although, compara-
tively, as distinct from the drive system and feelings of excite-
ment (Gilbert et al. 2008).
This stated that it is important to note that the above brief
description of the model in terms of emotions to nature is an
accessible simplification. Presented in such a manner allows
for the quick understanding, explanation and framing of re-
search findings related to how nature affects our mood states
and our physiology, and also acts as an emotional regulator. Of
note, in reference to the three circle model (i.e. Gilbert 2014),
the model is more complex and dynamic than as described
above with each of the three systems regulating each other
to produce blended affects. For example, affiliation is not just
linked with the contentment system, it can be linked to the
drive system (e.g. excitement about a social event or relation-
ship) or the threat system (e.g. anxiety when a loved one
becomes ill), just as both opioids and dopamine are linked to
pleasure and pain.
Importantly, it has recently been argued that evolutionary
aspects of human connection to nature have modern clinical
relevancy and nature should be part of established mental
health care (Mantler and Logan 2015). The three circle model
of affect regulation presented provides a foundation for
compassion-focused therapy (Gilbert 2009b,2014), thus
showing its utility for improving the understanding of mental
well-being and delivering successful mental health-care inter-
ventions. Certainly, the three circle model is used successfully
in both clinical and non-clinical settings alike to explain the
‘tricky brain’scenario and how the complexity of evolved and
dynamic brain systems interplays with our physical and men-
tal health. Its accessibility, for example, has led to its appear-
ance not only in research papers and training manuals but in
popular web forums such as ‘Netmums’, as a model to im-
prove health and happiness (Netmums 2016). This same mod-
el of affect regulation can be applied to explain the benefits
derived from nature (e.g. promotion of soothing affect) and to
guide interventions (e.g. ecotherapy) which aim to increase
well-being through our connection with nature.
Considering Types of Positive Affect
Despite the models of affect regulation presented above (most
notably the three circle model), and although Ulrich (1983)
outlined two types of positive affect (wakeful relaxation and
positive emotional reactions to nature), the majority of studies
into the benefits of nature, and a connection to nature, have
focused on and found increases in a single dimension of pos-
itive affect (see McMahan and Estes 2015 for review), without
Fig. 1 Three types of affect regulation system. From Gilbert (2009a),
The Compassionate Mind. With permission from Constable-Robinson
Evolutionary Psychological Science

considering specific types of positive affect or regulatory pro-
cesses. Howell and Passmore (2013) note that research into
positive affect and nature has had some mixed results and this
may be because aspects of hedonic well-being vary in their
relationship to nature affiliation, but also because positive af-
fect can be seen to cover vitality or drive and positive soothing
or contentment. They conclude that nature can elicit feelings
of ecstasy and wonder, and foster feelings of comfort.
Similarly, whilst the main approach in the emotion literature
is to apply a categorical approach to the structure of affect, the
above highlights the potential benefits of dimensional ap-
proaches where experience is much more than a single emo-
tion but felt core affect where importance is placed upon con-
tinuums of pleasure and arousal (see for instance Russell
2003).
Moreover, often overlooked is that neurophysiology re-
search has demonstrated two types of positive affect which
drive actions that go hand in hand with physiological changes
and autonomic support (Fredrickson 2001). The three circle
model also indicates two types of positive affect—drive and/
or contentment (Gilbert et al. 2008;Gilbert2014). Drive is
stimulating and activating, accompanied by joy, fun and ex-
citement (high pleasure, high arousal), but is also involved in
competitive drives. Drive seeking is linked to the sympathetic
nervous system, and over reliance can increase vulnerability
to depression, particularly where individuals are striving to
achieve in order to avoid inferiority or when individuals ex-
perience failures to obtaining a goal (Gilbert et al. 2007,2009;
Gilbert 2014). The second type of positive affect, content-
ment, affiliation and safeness, can often be overlooked.
These calming and soothing emotions (high pleasure, low
arousal) are regulating and can bring balance, toning down
the sympathetic threat and drive systems. This contentment
and affiliation system is linked to the parasympathetic nervous
system which is sometimes referred to as the ‘rest and digest’
arm (Porges 2007) and is associated with opiates and oxyto-
cin. This system is focused on restoration and affiliation and
can be compared to a mindful ‘being’, rather than ‘doing’
mode—and feeling more ‘connected’(Gilbert 2014). As
highlighted above, considering positive affect within the con-
text of the three circle model reveals two types of positive
affect: one associated with drive and feelings of excitement
and the other contentment and feelings of safeness and
connectedness.
Beyond Ulrich (1983), a search of the literature that con-
sidered terms including natural environment, positive affect,
affect regulation and neurophysiology found few papers that
considered the neurophysiology of emotion and models of
affect regulation within the context of the natural
environment. For example, Van den Berg et al. (2003)consid-
er cognitive (e.g. Kaplan 1995) and affective (e.g. Ulrich
1983) processes and provide a useful introduction to affect
and restoration with reference to regulation, without moving
into neurophysiology beyond mention of physiological
indicators of stress. Parsons (1991) considers the influence
of the natural environment on well-being within the context
of Henry’s(1980) model of neuro-endocrine responses and
LeDoux’s(1998) model of subcortical affective processing.
This work supports a proposal for two types of affect initiation
response systems within the context of immediate affective
responses to environmental stressors. Thus, their approach
provides insight into the impact of stressors in urban environ-
ments rather than positive affect of natural environments but is
rather dated.
Within the context of responses to nature, Ulrich
et al. (1991) note that activation of sympathetic nervous
system relates to readiness for action, consumes energy
and is therefore non-restorative. The parasympathetic
system functions to restore and maintain energy and
has a central role in attention and restoration. They rec-
ognise the need to disentangle the two systems when
considering responses to nature.
This entanglement is complex; as suggested above, affec-
tive emotions combine valence (positive-neutral-negative)
and arousal (activation-inhibition) (Russell 2003;Russell
and Barrett 1999). Previously, Watson and Tellegen (1985)
also suggested two related dimensions of positive affect:
pleasantness and activation. Activation refers to an arousal
or engagement continuum including relaxation, through alert-
ness to excitement. Pleasure relates to how well a person is
doing and can be viewed from differing conceptual stances,
for example positive-negative or approach-avoidance (Russell
2003; Russell and Barrett 1999). Thus, these two proposed
dimensions cover similar aspects as the three circle model
above, but utilise differing continuums. This and aspects of
the discussion above are included in Fig. 2to provide further
context to the three circle model. Affective pleasantness forms
part of hedonic well-being, along with a cognitive component
related to satisfaction of desires, and this form of well-being is
most often considered in nature connection and well-being
studies (Capaldi et al. 2014). Hedonic well-being can be seen
to include aspects of vitality and contentment, illustrating that
the three circle model of affect regulation is a simplification of
complex inter-relationships, but nonetheless useful for fram-
ing results and explaining the benefits of nature to various
stakeholders, many of whom, given the continued focus on
the biomedical and neurological basis, welcome reference to
underlying physiology when explaining the benefits of nature.
In summary, the three circle model of affect regulation pre-
sented provides a new perspective for the well-being benefits of
nature, interpretation of results and directions for future re-
search into understanding the benefits we find in nature. We
know that nature, and a connection to it, is restorative, bringing
thevitalityweneedinlife—but given the role of mindful at-
tention and self-reflection (Richardson and Sheffield 2015),
part of the story is about affiliation, soothing and contentment,
Evolutionary Psychological Science

and explicit assessment of this has often been neglected in
previous research.
Sympathetic-Parasympathetic Balance
Underpinning the affect regulation systems is the physiological
systems which bring about these states (of drive, contentment
and threat). The sympathetic nervous system is activating and
tends to be associated with states of threat or drive; in contrast,
the parasympathetic system is inhibitory but restorative and
soothing and associated with states of contentment. According
to Porges (1995,2007,2009), there are two branches of the vagal
nerve which feed into the sympathetic and parasympathetic sys-
tem: one is phylogenetically primitive and therefore unmyelinat-
ed. This branch acts as a quick route for stimulation of the sym-
pathetic nervous system in response to threats. The other branch
of the vagus nerve feeds into the parasympathetic nervous sys-
tem, and (in mammals) myelination of the vagus nerve evolved
to function as a ‘break’to tone-down sympathetic activity (threat
and drive), bringing about parasympathetic activity and content-
ment. This adaptation allowed humans to engage with attach-
ment and affiliative behaviours which are key for social engage-
ment (Porges 2007,2009) and, crucially, allow more soothing/
affiliative emotion regulation to take place. The balance between
these two branches is adaptive and beneficial to health and well-
being, as it reflects a system that is balanced between threat, drive
and contentment, with no single system (e.g. threat) dominating.
However, the interplay between these two branches can be com-
plex and produce blended patterns of positive affect (e.g. feeling
content but also excited; which is consistent with a dimensional
approach to emotion). It is not a simple case because as one
system increases the other decreases, nor are the systems mutually
exclusive; rather, it is the balance and dynamicity between both
systems that produces different physiological and mood states.
One way of investigating the balance between sympathetic
and parasympathetic systems, or between drive and contentment,
is heart rate variability (HRV). HRV is an established scientific
method for indicating changes in the autonomic nervous system,
in particular excitatory sympathetic and inhibitory parasympa-
thetic activity that controls the heart. It has been used to study
physiological changes related to exposure to nature (Brown et al.
2013;Gladwelletal.2012). In general, high total HRV indicates
good dynamic balance between the sympathetic and parasympa-
thetic system, whereas low total HRV suggests that the sympa-
thetic system dominates. Low HRV is linked to poor health and
well-being outcomes (Carney et al. 2005; Thayer et al. 2010).
Further, sympathetic mediators, such as threat, appear to exert
Fig. 2 Three circle model of affect regulation with dimensions of positive affect (informed by Gilbert 2014; Depue and Morrone-Strupinsky 2005;
Russell 2003; Watson and Tellegen 1985; Tinbergen 1951)
Evolutionary Psychological Science

their effects quickly and are reflected in the low-frequency power
of the HRV spectrum (Pomeranz et al. 1985). In contrast, vagal
mediators, such as contentment, exert their influence more quick-
ly on the heart and principally affect the high-frequency power of
the HRV spectrum. Therefore, this review will now consider
previous research into the benefits of nature using HRV indica-
tors to demonstrate sympathetic-parasympathetic activity and by
association, well-being (and emotions), to nature. The results are
tabulated to show the extent to which they concur with the out-
comes predicted by the three circle model; specifically, that (i)
drive seeking (and threat) is linked to the sympathetic nervous
system and will be lower in nature and (ii) contentment is linked
to the parasympathetic nervous system and will be higher in
nature.
Literature Search and Inclusion Criteria
A systematic search of the literature (Khan et al. 2003) was used
to locate studies for inclusion without any date restrictions.
Database searching considered combinations of a number of
keywords including natural environment,HRV,physiological,
positive affect and affect regulation. The reference sections of
relevant papers were studied and citation searches completed in
order to widen the search process. This process identified many
papers that discuss and review research. Criteria were set to iden-
tify those papers that reported primary research into nature expo-
sure whilst measuring HRV in comparison to an urban control.
The 14 nature exposure papers that met the inclusion criteria are
listed in Table 1with details of sample size, design and support
for the three circle model. A review study that reports a number
of primary studies is included. A book chapter and two foreign
language studies cited in English language papers were not in-
cluded as the design or number of participants could not be
ascertained.
Meta-analysis
All analyses were performed using meta-essentials (Van Rhee
et al. 2015). Thirteen eligible studies with a total of 871 par-
ticipants were included in the meta-analysis. First, analyses
were conducted and effect sizes calculated for each study
(Table 3). Specifically, we calculated dand confidence inter-
val (upper and lower) for studies that examined differences in
HRV indicators of parasympathetic activity (rMSSD, HF,
lnHF, SD1) and sympatho/parasympathetic balance (LF/HF
ratio; LF/LF+HF; LF; lnLF, SDRR, SD2). Then, for each, a
combined effect size was calculated and examined using the
Forest plot. Finally, publication bias was examined by calcu-
lating the fail safe N(Rosenthal 1979); because fail safe Nis
biased towards overestimating the number of null studies re-
quired to render the overall effect size non-significant (Carson
et al. 1990), a funnel plot of the standard error by the standard
mean differences was generated.
For parasympathetic activity, the Forest plot revealed a
combined effect size of Hedge’sg= 0.71 (CI 0.42 to 0.99,
p< 0.001, one-tailed) representing a medium effect
(Table 2). The overall effect size was somewhat heteroge-
neous (Q(13)= 57.64, p<0.001, I
2
= 79.18), thus indicating
that there are substantial heterogeneity issues, although no
study reported effects in the contra-expected direction.
Publication bias analyses were undertaken first by calculating
fail safe N(Rosenthal 1979). The fail safe Nwas 157, sug-
gesting that even if a great number of additional relevant stud-
ies with null results were included, the overall effect size
would remain significant. The distribution of the funnel plot
is symmetrical, suggesting no issues regarding publication
bias (see Fig. 3).
For sympatho/parasympathetic balance, the Forest plot re-
vealed a combined effect size of Hedge’sg=0.14 (CI−0.05 to
0.33, p= 0.05, one-tailed) representing a small effect
(Table 3). The overall effect size was somewhat homogeneous
(Q(13) = 27.24, p< 0.001, I
2
= 55.95), thus indicat ing that
there are some heterogeneity issues. Publication bias analyses
were undertaken first by calculating fail safe N(Rosenthal
1979). The fail safe Nwas 148. The distribution of the funnel
plot is symmetrical, suggesting no issues regarding publica-
tion bias (see Fig. 4).
Nature and HRV Research Discussion
Importantly, the review of each study revealed that they do not
consider their results in the context of affect regulation; in-
deed, many of the studies do not consider affect, having an
autonomic nervous system or stress reduction theory (SRT)
focus. Many of the studies identified consider forest bathing in
Japan (Shinrin-yoku). Although the forest-based studies lack
the control of the laboratory, Kappas (2011) is critical of lab-
based research into emotional response, and McMahan and
Estes (2015) found that across 32 studies, there was no signif-
icant difference in positive affect responses to real nature vs
lab-based nature images/videos. Of the studies identified, all
provide full or partial support for the three circle model, with
the meta-analysis confirming greater parasympathetic activity
and somewhat lower sympathetic activity in the nature expo-
sure conditions compared with the urban control conditions.
Partial support occurs where significant differences in sympa-
thetic nervous activity were not found, which is a point of
discussion below.
In terms of the three circle model, the vast majority of
results show that natural environments promote greater para-
sympathetic nerve activity (contentment) and lower sympa-
thetic nerve activity (drive) than urban environments, with
medium and small effect sizes found in the meta-analyses,
Evolutionary Psychological Science

respectively. An issue in the current context with such com-
parison to control studies is the observation that HRV in nature
could remain the same, with urban environments stimulating
sympathetic activity. It could then be argued that changes
within the urban environments are actually responsible for
the production of significant differences. Of importance here
however, whilst few of the included studies consider temporal
analysis, three studies do indicate within-group temporal
changes for components of HRV (Tsunetsugu et al. 2007;
Song et al. 2015; Lee et al. 2014). The excluded book chapter
also reported significant differences in changes in HRV (Lee
et al. 2012). Therefore, there can be confidence that it is in fact
nature bringing benefits, rather than urban environments re-
moving them.
Recent results by Kobayashi et al. (2015) reveal interesting
detail. Mirroring the medium and small effect sizes found in
the meta-analysis, they noted that approximately 80 % of par-
ticipants showed an increase in the parasympathetic indicator
of HRV, and 64 % showed decreases in the sympathetic indi-
cator of HRV; the remaining participants showed opposite
responses. This raises the question as to the role of threat,
anxiety and phobias in natural environments (e.g. some envi-
ronments contain features which may have been a threat to
survival in our evolutionary history). Certainly, it is known
that evolution has provided us with a set of ‘primed’emotion-
al responses which result in rapid selective learning and great
difficulty in extinguishing such responses (see for example the
seminal work of Mineka et al. 1984). Not surprisingly, there-
fore, Kobayashi et al. (2015) note that some people with
biophobia (Kellert 1993) report a strong dislike for natural
environments, and this includes specific phobias such as
arachnophobia. People with arachnophobia showed increased
heartrateduringpresentationofimagesorthoughtsofspiders.
It can further be seen that eight of the studies measured
anxiety, most often using POMS, all finding lower anxiety
in the natural environment. However, those studies did not
report analysis on anxiety as a potential barrier to positive
HRV changes which may prove essential for our further un-
derstanding of the relationship between nature and positive
emotions (especially given selective learning of primed emo-
tions). Further, the three circle model presented, albeit simple,
extends a number of emotion regulation models that have
Tabl e 1 Nature exposure studies that measure HRV
Study Pps Design Greater
parasympathetic
Lower
sympathetic
Supports
three circles
Lower anxiety
Brown et al. (2013) 25 Lab-based nature vs
urban control
Higher than control Not tested P n/a
Gladwell et al. (2012) 29 Lab-based nature vs
urban control
Higher than control Not tested Y n/a
Horiuchi et al. (2014) 15 Forest view vs no
view control
Not significant vs control,
but significant effect
of time
Not significant P Y
Kobayashi et al. (2015) 625 Forest vs urban
control
80 % higher than control 64 % lower than control Y n/a
Lee et al. (2011)12Forestvsurban
control
Higher than control Lower than control Y Y
Lee et al. (2014) 40-44 Forest vs urban
control
Higher than control Lower than control Y Y
Lee et al. 2015) 12 Rural vs urban
control
Higher than control Lower than control Y Y
Park et al. 2008)12Forestvsurban
control
Higher than control Not significant P n/a
Park et al. (2009) 9 Forest vs urban
control
Higher than control Lower than control Y n/a
Park et al. (2010) n/a Review Higher than control Lower than control Y Y
Song et al. (2013a,b)36 Forestvsurban
control
Higher than control Not significant P n/a
Song et al. (2013b)13Parkvsurban
control
Higher than control Not significant (p= 0.06) P Y
Song et al. (2015) 19 Lab-based nature vs
urban control
Higher than control Not significant P Y
Tsu netsu gu e t al. ( 2007)5–12 Forest vs urban
control
Higher at selected time
points
Lower than control Y n/a
Tsu netsu gu e t al. ( 2013)41–44 Forest vs urban
control
Higher at selected time
points
Lower than control Y Y
Results support etc.: Yyes, Ppartial, Nno
Evolutionary Psychological Science

come before it, by including physiological indices of sympa-
thetic activity and indicating that such activity can also be
linked to stimulation, joy and excitement. Therefore, there is
the potential for increased sympathetic activity, rather than a
decrease, in more connected individuals who report increased
vitality in nature (Capaldi et al. 2014). Finally, the approach to
sympathetic-related measures varied considerably. These con-
founding factors could lead to the smaller differences in the
sympathetic measurements, which achieved one-tailed signif-
icance with a smaller effect size in the meta-analysis.
Subsequently, there is a need for further consideration of
individual differences and physiological responses. People
who are more connected with nature experience greater psy-
chological benefits from contact with nature (Hartig et al.
2011). Mindful attention and self-reflection are two further
aspects associated with greater connection to nature
(Richardson and Sheffield 2015). Further, it has been
shown that spirituality (Kamitsis and Francis 2013)and
engagement with natural beauty (Zhang et al. 2014)are
involved in the relationship between nature connectedness
and well-being. It is worth noting that Berridge (2009)pro-
poses that positive emotions may use sensory pleasure circuits,
bringing about a link between aesthetic enjoyment and positive
consummatory states (Kappas 2011). Whilst the idea of pleasure
circuits is not new and has been briefly reviewed prior to the
presentation of the three circle model, this could well explain
Zhang’s finding that engaging with nature’s beauty was required
for well-being benefits. Last but not least, there may also be
0
0.05
0.1
0.15
0.2
0.25
0.3
0.35
0.4
0.45
0.5
-0.5 0 0.5 1 1.5 2 2.5
Standard error
Effect Size
Studies Imputed Data Points Observed CES Adjusted CES
Fig. 3 Funnel plot of standard
error by standard differences in
the means of parasympathetic
measures
Tabl e 2 Parasympathetic studies
Study name Hedges’gCI Lower
limit
CI upper
limit
Weight (%)
Brown et al. (2013) 0.57 0.14 1 8.54
Gladwell et al. (2012)0.24 −0.13 0.62 9.08
Horiuchi et al. (2014)0.22 −0.3 0.75 7.79
Kobayashi et al. (2015) 0.97 0.87 1.06 11.21
Lee et al. (2011)0.65−0.12 1.42 6.16
Lee et al. (2014) 0.47 0.14 0.8 9.47
Lee et al. (2015) 1.17 0.38 1.95 5.77
Park et al. (2008)0.59−0.05 1.23 6.90
Park et al. (2009)0.63−0.09 1.35 6.43
Song et al. (2013a,b) 1.48 0.82 2.15 6.44
Song et al. (2013b) 0.63 0.01 1.26 7.02
Song et al. (2015) 1.92 1.14 2.69 5.56
Tsu netsu gu e t al. ( 2013)0.3 −0.01 0.62 9.61
Evolutionary Psychological Science

differences in those who come from rural or urban envi-
ronments, differences based on individual’s motivations
for visiting green spaces (e.g. rest and relaxation, adven-
ture, challenge, work) and what activities they engage in
there. This could all influence the blend of emotions derived
from being in nature and attests to the importance of dimen-
sional approaches when considering emotions in nature. None
of the studies in the meta-analysis explicitly explore these
factors. Here therefore we are in agreement with Van den
Berg et al. (2003) who argue that more research taking in
different scenarios, different types of green and blue settings
and different groups of participants is needed to gain further
understanding of the physiological and psychological path-
ways between natural spaces and well-being.
In sum, the three circle model provides a frame-
work for considering the benefits of nature and pro-
vides direction for further research. It is drawn from
preceding emotion regulation literature and has been
shown to fit with literature on a dimensional approach
to emotion and positive affect. Albeit presented here in a
simplified accessible format, there is scope for the model to
explain the varying HRV results by considering the role of
anxiety in reducing benefits. Further, nature connectedness
mediates the well-being benefits of nature (Richardson
et al. 2016) and will therefore mediate the benefits revealed
by HRV measurements. Finally, engagement with natural
beauty, self-reflection and mindful attention may also ex-
plain the differences in individuals’response to natural
0
0.05
0.1
0.15
0.2
0.25
0.3
0.35
0.4
0.45
-1.5 -1 -0.5 0 0.5 1 1.5
Standard error
Effect Size
Studies Imputed Data Points Observed CES Adjusted CES
Fig. 4 Funnel plot of standard
error by standard differences in
the means of sympathetic-
parasympathetic balance
measures
Tabl e 3 Sympathetic-
parasympathetic balance studies Study name Hedges’gCI lower
limit
CI upper
limit
Weight (%)
Brown et al. (2013)0 −0.4 0.4 8.35
Gladwell et al. (2012)0.25 −0.12 0.63 8.80
Horiuchi et al. (2014)0.22 −0.3 0.75 6.34
Kobayashi et al. (2015) 0.32 0.24 0.4 16.33
Lee et al. (2011)0 −0.68 0.68 4.95
Lee et al. (2014) 0.44 0.11 0.76 9.83
Lee et al. (2015)−0.98 −1.72 −0.25 4.16
Park et al. (2008)0 −0.59 0.59 5.73
Park et al. (2009)0.63−0.09 1.35 4.46
Song et al. (2013a,b)0 −0.45 0.45 7.49
Song et al. (2013b)0.31 −0.26 0.89 5.76
Song et al. (2015)0 −0.45 0.45 7.49
Tsu netsu gu e t al. ( 2013)0.03 −0.28 0.34 10.32
Evolutionary Psychological Science

environments, but can all be accounted for in terms of the
three circle model.
Conclusions
The purpose of this brief review was to highlight the need to
link emotional responses to affect regulation (Kappas 2011)
and present evidence to support the application of an existing
and accessible evolutionary functional three circle model of
emotion and affect regulation within the context of the well-
being benefits of nature. A key outcome of this process is the
reminder to focus on the two types of positive affect that can
explain previous mixed results (Howell and Passmore 2013),
as well as consider a dimensional approach to emotion in
nature.
It is also possible to consider previous nature and well-
being research using subjective measures within the context
of the three circle model. A further review of the nature and
well-being literature placing it into the context of the model is
beyond the scope of the current review which focusses on
proposing and evidencing the three circle model with relevant
HRV studies. Therefore, examples broadly considering the
three main aspects of the model, including the two types of
positive affect, are used to illustrate its wider utility. For ex-
ample, there has been a body of research that considers posi-
tive outcomes of nature engagement, such as improved vitality
(Capaldi et al. 2014). This body of work can be mapped onto
the drive aspect within the context of stimulation,joy and high
arousal/high pleasure. In contrast, work on mindful attention
and reflection (e.g. Richardson and Sheffield 2015;Howell
et al. 2011) can be mapped onto the contentment aspect within
the context of calm and low arousal/high pleasure. Finally,
barriers to nature such as rumination and neuroticism
(Richardson and Sheffield 2015) as well as potential selective-
ly learnt anxieties can be mapped onto the threat dimension.
The model can also be considered within the context of
existing theories regarding the benefits of nature. Psycho-
evolutionary SRT focuses on restoration after stress (Ulrich
et al. 1991). SRT suggests increased positive affect, with the
three circle model highlighting the need to consider both
contentment and drive. The model can also be seen to
include physiological arousal based on physiological
adaptation to natural environments. Further, Mantler and
Logan (2015) note that emotion is central to SRT; hence, fol-
lowing Kappas (2011), there is a need to consider affect
regulation.
The attention restoration theory (ART) (Kaplan 1995)
focusses on directed attention which requires non-salient
distracters to be ignored, which brings cognitive effort.
Directed attention, which can be compared to drive and some-
times threat, is common in modern life and ART proposes that
natural environments are restorative. Its soft fascination
provides involuntary attention which facilities calm, rest and
contemplation (Beute and Kort 2014), thereby bringing the
desired balance between the three aspects of the three circle
affect regulation model.
ARTand SRT are both based on restoration, but Beute and
Kort (2014) used HRV as an indicator of exertion of self-
control and challenged the proposition that nature primarily
provides restorative benefits, as results showed beneficial ef-
fects of nature when resources had not been depleted. The
three circle model of affect regulation supports this account
and encourages a perspective of wellness through balance.
Nature can bring both joy and excitement and contentment
and affiliation. Both are argued to bring a balanced emotional
state and it is known that imbalance can lead to affective
disorders (e.g. mania is associated with excessive drive, arous-
al and extreme euphoria). In terms of general well-being, the
model allows for nature to be restorative and reduce stressors,
whilst also highlighting that natural environments may not
feel safe to some.
The three circle model also provides a tested framework in
which to consider positive affect and the mental well-being
and the benefits of nature. For example, stimulation of our
contentment system is a goal of psychological therapies such
as compassion-focused therapy. If natural environments can
be used to stimulate this type of positive affect regulation
system, nature can potentially be used to tone-down the threat
system and bring about positive physiological change in the
body. This would improve parasympathetic-sympathetic bal-
ance as indicated by the HRV literature above. Adding support
for this argument, it is now well recognised that exercises used
within CFT influence brain and bodily responding (see for
example Duarte et al. 2015; Longe et al. 2010).
Finally, the three circle model can be easily understood in
the context of our everyday lives and the model is accessible
to all. Crucially, the model in its present state provides a nar-
rative for the lay person to understand the benefits of nature
whilst providing a convincing physiological basis for those
not convinced by more subjective emotional accounts.
References
Averbeck, B. B., & Seo, M. (2008). The statistical neuroanatomy of
frontal networks in the macaque. PLoS Computational Biology,
4(4), e1000050.
Berridge, K. C. (2009). Wanting and liking: observations from the neu-
roscience and psychology laboratory. Inquiry, 52(4), 378–398.
Beute, F., & Kort, Y. A. (2014). Salutogenic effects of the environment:
review of health protective effects of nature and daylight. Applied
Psychology: Health and Well-Being, 6(1), 67–95.
Bressan, R. A., & Crippa, J. A. (2005). The role of dopamine in reward
andpleasurebehaviour—review of data from preclinical research.
Acta Psychiatrica Scandinavica, 111(s427), 14–21.
Evolutionary Psychological Science

Brown, D. K., Barton, J. L., & Gladwell, V. F. (2013). Viewing nature
scenes positively affects recovery of autonomic function following
acute-mental stress. Environmental Science & Technology, 47(11),
5562–5569.
Capaldi, C. A., Dopko, R. L., & Zelenski, J. M. (2014). The relationship
between nature connectedness and happiness: a meta-analysis.
Frontiers in Psychology, 5,976.
Carney, R. M., Blumenthal, J. A., Freedland, K. E., Stein, P. K., Howells,
W. B., Berkman, L. F., Watkins, L. L., Czajkowski, S. M., Hayano,
J., Domitrovich, P. P., & Jaffe, A. S. (2005). Low heart rate variabil-
ity and the effect of depression on post-myocardial infarction mor-
tality. Archives of Internal Medicine, 165(13), 1486–1491.
doi:10.1001/archinte.165.13.1486.
Carson, K. P., Schriesheim, C. A., & Kinicki, A. J. (1990). The usefulness
of the “fail-safe”statistic in meta-analysis. Educational and
Psychological Measurement, 50(2), 233–243.
Cho, M. M., DeVries, A. C., Williams, J. R., & Carter, C. S. (1999). The
effects of oxytocin and vasopressin on partner preferences in male
and female prairie voles (Microtus ochrogaster). Behavioral
Neuroscience, 113(5), 1071.
Darwin, C. (1872). 1965. The expressions of the emotions in man and
animals. Chicago: The University of Chicago Press.
de Almeida, J. R. C., Versace, A., Mechelli, A., Hassel, S., Quevedo, K.,
Kupfer, D. J., & Phillips, M. L. (2009). Abnormal amygdala-
prefrontal effective connectivity to happy faces differentiates bipolar
from major depression. Biological Psychiatry, 66(5), 451–459.
Depue, R. A., & Morrone-Strupinsky, J. V. (2005). A neurobehavioral
model of affiliative bonding. Behavioral and Brain Sciences, 28,
313–395.
Duarte, J., McEwan, K., Barnes, C., Gilbert, P., & Maratos, F. A. (2015).
Do therapeutic imagery practices affect physiological and emotional
indicators of threat in high self‐critics? Psychology and
Psychotherapy: Theory, Research and Practice, 88(3), 270–284.
Etkin, A. (2009). Functional neuroanatomy of anxiety: a neural circuit
perspective. In Behavioral neurobiology of anxiety and its treatment
(pp. 251–277). Berlin: Springer.
Etkin, A., Büchel, C., & Gross, J. J. (2015). The neural bases of emotion
regulation. Nature Reviews Neuroscience, 16(11), 693–700.
Fox, A. S., Oler, J. A., Tromp, D. P., Fudge, J. L., & Kalin, N. H. (2015).
Extending the amygdala in theories of threat processing. Trends in
Neurosciences, 38(5), 319–329.
Fredrickson, B. L. (2001). The role of positive emotions in positive psy-
chology: the broaden-and-build theory of positive emotions.
American Psychologist, 56(3), 218.
Frijda, N. H. (1987). Emotion, cognitive structure, and action tendency.
Cognition and Emotion, 1(2), 115–143.
Park, B. J., Tsunetsugu, Y., Hirano, H., Kagawa, T., & Miyazaki, Y.
(2007). Physiological evaluation of the effects of Shinrinyoku (tak-
ing in the atmosphere of the forest) in Kayanodaira Highland,
Kijimadaira Village, Nagano Prefecture (in Japanese). Kanto
Journal of Forest Research, 58,219–222.
Jones, M. V., Hurst, G., Masterson, D., Clark-Carter, D., Tarvainen, M. P.,
Smith, G., & Nieuwenhuijsen, M. (2015). Where to put your best
foot forward: psycho-physiological responses to walking in natural
and urban environments. Journal of Environmental Psychology.
doi:10.1016/j.jenvp.2015.11.003.
Gilbert, P. (2005). Compassion: conceptualisations, research and use in
psychotherapy. Oxford: Routledge.
Gilbert, P. (2009a). The compassionate mind: a new approach to the
challenges of life. London: Constable & Robinson.
Gilbert, P. (2009b). Introducing compassion-focused therapy. Advances
in Psychiatric Treatment, 15(3), 199–208.
Gilbert, P. (2014). The origins and nature of compassion focused therapy.
British Journal of Clinical Psychology, 53(1), 6–41.
Gilbert, P., Broomhead, C., Irons, C., McEwan, K., Bellew, R., Mills, A.,
& Gale, C. (2007). Striving to avoid inferiority: scale development
and its relationship to depression, anxiety and stress. British Journal
of Social Psychology, 46,633–648.
Gilbert, P., McEwan, K., Mitra, R., Franks, L., Richter, A., & Rockliff, H.
(2008). Feeling safe and content: a specific affect regulation system?
Relationship to depression, anxiety, stress, and self-criticism. The
Journal of Positive Psychology, 3(3), 182–191.
Gilbert, P., McEwan, K., Bellew, R., Mills, A., & Gale, C. (2009). The
dark side of competition: how competitive behaviour and striving to
avoid inferiority are linked to depression, anxiety, stress and self
harm. Psychology and Psychotherapy: Theory, Research and
Practice, 82,123–136.
Gladwell, V. F., Brown, D. K., Barton, J. L., Tarvainen, M. P., Kuoppa, P.,
Pretty, J., Suddaby, J. M., & Sandercock, G. R. H. (2012). The
effects of views of nature on autonomic control. European Journal
of Applied Physiology, 112(9), 3379–3386.
Graustella, A. J., & MacLeod, C. (2012). A critical review of the influ-
ence of oxytocin nasal spray on social cognition in humans: evi-
dence and future directions. Hormones and Behavior, 61(3), 410–
418.
Gray, J. A. (1982). On mapping anxiety. Behavioral and Brain Sciences,
5(03), 506–534.
Hartig, T., van den Berg, A. E., Hagerhall, C. M., Tomalak, M., Bauer, N.,
Hansmann, R., Ojala, A., Syngollitou, E., Carrus, G., van Herzele,
A., & Bell, S. (2011). Health benefits of nature experience: psycho-
logical, social and cultural processes. In K. Nilsson, M. Sangster, C.
Gallis, K. De Vries, K. Seeland, & J. Schipperijn (Eds.), Forests,
trees and human health (pp. 127–168). New York: Springer.
Henry, J. P. (1980). Present concept of stress theory. In E. Ursdin, R.
Kvetnansky, & I. J. Kopin (Eds.), Catecholamines and stress: recent
advances (pp. 557–571). New York: Elsevier.
Horiuchi, M., Endo, J., Takayama, N., Murase, K., Nishiyama, N., Saito,
H., & Fujiwara, A. (2014). Impact of viewing vs. not viewing a real
forest on physiological and psychological responses in the same
setting. International Journal of Environmental Research and
Public Health, 11(10), 10883–10901.
Howell, A. J., & Passmore,H. A. (2013). The nature of happiness: nature
affiliation and mental well-being. In C. L. M. Keyes (Ed.), Mental
well-being (pp. 231–257). New York: Springer.
Howell, A. J., Dopko, R. L., Passmore, H. A., & Buro, K. (2011). Nature
connectedness: associations with well-being and mindfulness.
Personality and Individual Differences, 51(2), 166–171.
Kamitsis, I., & Francis, A. J. (2013). Spirituality mediates the relationship
between engagement with nature and psychological wellbeing.
Journal of Environmental Psychology, 36, 136–143.
Kaplan, S. (1995). The restorative benefits of nature: toward an integra-
tive framework. Journal of Environmental Psychology, 15(3), 169–
182.
Kappas, A. (2011). Emotion and regulation are one! Emotion Review,
3(1), 17–25.
Kellert, S. R. (1993). The biological basis for human values of nature. In
S. R. Kellert & E. O. Wilson (Eds.), The biophilia hypothesis (pp.
42–69). Washington: Island Press.
Khan, K. S., Kunz, R., Kleijnen, J., & Antes, G. (2003). Five steps to
conducting a systematic review. Journal of the Royal Society of
Medicine, 96(3), 118–121.
Kobayashi, H., Song, C., Ikei, H., Kagawa, T., & Miyazaki, Y. (2015).
Analysis of individual variations in autonomic responses to urban
and forest environments. Evidence-Based Complementary and
Alternative Medicine, 2015.
LeDoux, J. (1998). The emotional brain. London: Weidenfeld and
Nicolson.
LeDoux, J. E. (2014). Coming to terms with fear. Proceedings of the
National Academy of Sciences, 111(8), 2871–2878.
Lee, J., Park, B. J., Tsunetsugu, Y., Ohira, T.,Kagawa, T., & Miyazaki, Y.
(2011). Effect of forest bathing on physiological and psychological
Evolutionary Psychological Science

responses in young Japanese male subjects. Public Health, 125(2),
93–100.
Lee, J., Park, B. J., Tyrväinen, L., Li, Q., Kagawa, T., Miyazaki, Y., &
Tsunetsugu, Y. (2012). Nature therapy and preventive medicine.
INTECH Open Access Publisher.
Lee, J., Tsunetsugu, Y., Takayama, N., Park, B. J., Li, Q., Song, C., &
Miyazaki, Y. (2014). Influence of forest therapy on cardiovascular
relaxation in young adults. Evidence-Based Complementary and
Alternative Medicine, 69(2), 104–110.
Lee, J., Park, B. J., Ohira, T., Kagawa, T., & Miyazaki, Y. (2015). Acute
effects of exposure to a traditional rural environment on urban
dwellers: a crossover field study in terraced farmland.
International Journal of Environmental Research and Public
Health, 12(2), 1874–1893.
Leknes, S., & Tracey, I. (2008). A common neurobiology for pain and
pleasure. Nature Reviews Neuroscience, 9(4), 314–320.
Lindquist, K. A., Wager, T. D., Kober, H., Bliss-Moreau, E., & Barrett, L.
F. (2012). The brain basis of emotion: a meta-analytic review.
Behavioral and Brain Sciences, 35(03), 121–143.
Longe, O., Maratos, F. A., Gilbert, P., Evans, G., Volker, F., Rockliff, H.,
& Rippon, G. (2010). Havinga word with yourself: neural correlates
of self-criticism and self-reassurance. NeuroImage, 49(2), 1849–
1856.
MacLean, P. D. (1949). Psychosomatic disease and the “visceral brain”:
recent developments bearing on the Papez theory of emotion.
Psychosomatic Medicine, 11(6), 338–353.
MacLean, P. D. (1990). The triune brain in evolution: role in
paleocerebral functions. New York: Plenum.
Mantler, A., & Logan, A. C. (2015). Natural environments and mental
health. Advances in Integrative Medicine, 2(1), 5–12.
Maratos, F. A., Mogg, K., Bradley, B. P., Rippon, G., & Senior, C. (2009).
Coarse threat images reveal theta oscillations in the amygdala: a
magnetoencephalography study. Cognitive, Affective, &
Behavioral Neuroscience, 9(2), 133–143.
McMahan, E. A., & Estes, D. (2015). The effect of contact with natural
environments on positive and negative affect: a meta-analysis. The
Journal of Positive Psychology, 10(6), 507–519.
Méndez-Bértolo, C., Moratti, S., Toledano, R., Lopez-Sosa, F., Martínez-
Alvarez,R.,Mah,Y.H.,…& Strange, B. A. (2016). A fast pathway
for fear in human amygdala. Nature Neuroscience.
Mineka, S., Davidson, M., Cook, M., & Keir, R. (1984). Observational
conditioning of snake fear in rhesus monkeys. Journal of Abnormal
Psychology, 93(4), 355.
Nave, G., Camerer, C., & McCullough, M. (2015). Does oxytocin in-
crease trust in humans? A critical review of research. Perspectives
on Psychological Science, 10(6), 772–789.
Netmums (2016). CMA: the three circles model. Retrieved from: www.
netmums.com/woman/health-and-happiness/making-mums-
happy/cma-the-three-circles-model.
Ochsner, K. N., Silvers, J. A., & Buhle, J. T. (2012). Functional imaging
studies of emotion regulation: a synthetic review and evolving mod-
el of the cognitive control of emotion. Annals of the New York
Academy of Sciences, 1251(1), E1–E24.
Olds, J. (1956). Pleasure centers in the brain. Scientific American, 195,
105–117.
Panksepp, J. (1998a). Affective neuroscience.NewYork:Oxford
University Press.
Panksepp, J. (1998b). Affective neuroscience: the foundations of human
and animal emotions. Oxford: Oxford University Press.
Papez, J. W. (1937). A proposed mechanism of emotion. Archives of
Neurology & Psychiatry, 38(4), 725–743.
Park, B. J., Tsunetsugu, Y., Ishii, H., Furuhashi, S., Hirano, H., Kagawa,
T., & Miyazaki, Y. (2008). Physiological effects of Shinrin-yoku
(taking in the atmosphere of the forest) in a mixed forest in
Shinano Town, Japan. Scandinavian Journal of Forest Research,
23(3), 278–283.
Park, B. J., Tsunetsugu, Y., Kasetani, T., Morikawa, T., Kagawa, T., &
Miyazaki, Y. (2009). Physiological effects of forest recreation in a
young conifer forest in Hinokage Town,Japan. Silva Fennica, 43(2),
291–301.
Park, B. J., Tsunetsugu, Y., Kasetani, T., Kagawa, T., & Miyazaki, Y.
(2010). The physiological effects of Shinrin-yoku (taking in the
forest atmosphere or forest bathing): evidence from field experi-
ments in 24 forests across Japan. Environmental Health and
Preventive Medicine, 15(1), 18–26.
Parsons, R. (1991). The potential influences of environmental perception
on human health. Journal of Environmental Psychology, 11(1), 1–
23.
Pedersen, C. A., Caldwell, J. D., Walker, C., Ayers, G., & Mason, G. A.
(1994). Oxytocin activates the postpartum onset of rat maternal be-
havior in the ventral tegmental and medial preoptic areas.
Behavioral Neuroscience, 108(6), 1163.
Pessoa, L. (2014). Understanding brain networks and brain organization.
Physics of Life Reviews, 11(3), 400–435.
Phelps, E. A., & Ledoux, J. E. (2005). Contributions of the amygdala to
emotion processing: from animal models to human behavior.
Neuron, 48,175–187.
Pomeranz, B., Macaulay, R. J., Caudill, M. A., Kutz, I., Adam, D.,
Gordon, K. M., Kilborn, A. C., Barger, D. C., Shannon, Cohen, R.
J., & Benson, H. (1985). Assessment of autonomic function in
humans by heart rate spectral analysis. American Journal of
Physiology—Heart and Circulatory Physiology, 248(1), H151–
H153.
Porges, S. W. (1995). Orienting in a defensive world: mammalian mod-
ifications of our evolutionary heritage: a polyvagal theory.
Psychophysiology, 32,301–318.
Porges, S. W. (2007). The polyvagal perspective. Biological Psychology,
74(2), 116–143.
Porges, S. W. (2009). The polyvagal theory: new insights into adaptive
reactions of the autonomic nervous system. Cleveland Clinic
JournalofMedicine,76(Suppl 2), S86.
Richardson, M., & Sheffield, D. (2015). Reflective self-a ention: A more
stable predictor of connection to nature than mindful attention.
Ecopsychology, 7(30),166–175.
Richardson, M., Cormack, A., McRobert, L., & Underhill, R. (2016). 30
days wild: development and evaluation of a large-scale nature en-
gagement campaign to improve well-being. PLoS ONE, 11(2),
e0149777. doi:10.1371/journal.pone.0149777.
Rosenthal, R. (1979). The file drawer problem and tolerance for null
results. Psychological Bulletin, 86(3), 638.
Russell, J. A. (2003). Core affect and the psychological construction of
emotion. Psychological Review, 110(1), 145.
Russell, J. A., & Barrett, L. F. (1999). Core affect, prototypical emotional
episodes, and other things called emotion: dissecting the elephant.
Journal of Personality and Social Psychology, 76(5), 805.
Song, C., Ikei, H., Tsunetsugu, Y., Lee, J., Kagawa, T., & Miyazaki, Y.
(2013a). Physiological and psychological impacts of walking stress
in an urban environment on young males. Journal of Geography
and Natural Disasters, 3, 113.
Song, C., Joung, D., Ikei, H., Igarashi, M., Aga, M., Park, B. J., …&
Miyazaki, Y. (2013). Physiological and psychological effects of
walking on young males in urban parks in winter. Journal of
Physiological Anthropology, 32(1), 1.
Song, C., Ikei, H., Kobayashi, M., Miura, T., Taue, M., Kagawa, T., Li,
Q., Kumeda, S., Imai, M., & Miyazaki, Y. (2015). Effect of forest
walking on autonomic nervous system activity in middle-aged hy-
pertensive individuals: a pilot study. International Journal of
Environmental Research and Public Health, 12(3), 2687–2699.
Thayer, J. F., Yamamoto, S. S., & Brosschot, J. F. (2010). The relationship
of autonomic imbalance, heart rate variability and cardiovascular
disease risk factors. International Journal of Cardiology, 141(2),
122–131. doi:10.1016/j.ijcard.2009.09.543.
Evolutionary Psychological Science

Tinbergen, N. (1951). The study ofinstinct. New York: Oxford University
Press.
Tsunetsugu, Y., Park, B. J., Ishii, H., Hirano, H., Kagawa, T., & Miyazaki, Y.
(2007). Physiological effects of Shinrin-yoku (taking in the atmosphere
of the forest) in an old-growth broadleaf forest in Yamagata Prefecture,
Japan. Journal of Physiological Anthropology, 26(2), 135–142.
Tsunetsugu, Y., Lee, J., Park, B. J., Tyrväinen, L., Kagawa, T., &
Miyazaki, Y. (2013). Physiological and psychological effects of
viewing urban forest landscapes assessed by multiple measure-
ments. Landscape and Urban Planning, 113,90–93.
Ulrich, R. S. (1983). Aesthetic and affective response to natural environ-
ment. In I. Altman & J. Wohlwill (Eds.), Behavior and the natural
environment (pp. 85–125). New York: Plenum.
Ulrich, R. S., Simons, R. F., Losito, B. D., Fiorito, E., Miles, M. A., &
Zelson, M. (1991). Stress recovery during exposure to natural and
urban environments. Journal of Environmental Psychology, 11(3),
201–230.
Van den Berg, A. E., Koole, S. L., & van der Wulp, N. Y. (2003).
Environmental preference and restoration: (how) are they related?
Journal of Environmental Psychology, 23(2), 135–146.
Van Rhee, H. J., Suurmond, R., & Hak, T. (2015). User manual for meta-
essentials: workbooks for meta-analysis (version 1.0).Rotterdam:
Erasmus Research Institute of Management. Retrieved from www.
erim.eur.nl/research-support/meta-essentials.
Watson, D., & Tellegen, A. (1985). Toward a consensual structure of
mood. Psychological Bulletin, 98(2), 219.
Wilson, E. O. (1984). Biophilia. Cambridge: Harvard University Press.
Wilson, E. O. (1992). The diversity of life. London: Penguin.
Zhang, J. W., Howell, R. T., & Iyer, R. (2014). Engagement with natural
beauty moderates the positive relation between connectedness with
nature and psychological well-being. Journal of Environmental
Psychology, 38,55–63.
Evolutionary Psychological Science