Vol.3, No.8, 723-727
opyright © 2011 SciRes. Openly accessible at http://www.scirp.org/journal/NS/
(2011) Natural Science
Perceived happiness level influences evocation of
positive emotions
Masahiro Matsunaga1*, Hiroki Murakami2, Kaori Yamakawa3, Tokiko Isowa4,
Seisuke Fukuyama5, Jun Shinoda5, Jitsuhiro Yamada5, Hideki Ohira3
1Division of Cerebral Integration, Department of Cerebral Research, National Institute for Physiological Sciences, Aichi, Japan;
*Corresponding Author: mmatsu@nips.ac.jp
2Department of Psychology, Stony Brook University, New York, USA;
3Department of Psychology, Graduate School of Environmental Studies, Nagoya University, Aichi, Japan;
4Faculty of Nursing, Graduate School of Medicine, Mie University, Mie, Japan;
5Chubu Medical Center for Prolonged Traumatic Brain Dysfunction, Kizawa Memorial Hospital, Gifu, Japan.
Received 12 April 2011; revised 30 April 2011; accepted 5 May 2011.
Happiness is a positive feeling characterized by
satisfaction, joy, pleasure, or love. Perceived
happiness level is likely associated with health
and well-being. However, the neurobiological
mechanisms underlying the positive effects of
happiness on psychological and physiological
wellness remain obscure. In this study, we
found that the medial prefrontal cortex (MPFC)
was strongly activated and positive emotions
were strongly evoked in individuals with high
perceived happiness levels compared to those
with low perceived happiness lev els when either
looked at a favorite person. Moreover, positive
mood changes were positively correlated with
MPFC activity. These results show that per-
ceived happiness level is associated with posi-
tive emotion evocation by means of the MPFC
function, which may be involved in psycho-
logical and physiological wellness. Therefore,
happiness may play an important role in psy-
chological and physiological wellness.
Keywords: Happiness; Medial Prefrontal Cortex;
Attraction; Positron Emission Tomogr aphy
Stress and anxiety can lead to depression [1]. Psycho-
neuroimmunological studies have shown that psychoso-
cial stressors can activate the sympathetic nervous sys-
tem and that prolonged elevation of sympathetic nervous
activity weakens immune defense mechanisms [2]. There-
fore, stress and anxiety may cause or facilitate not only
depression but several other diseases as well, including
cancer [3].
The idea that perceived happiness level may be asso-
ciated with health and well-being has recently been ex-
plored. Individuals with a high level of perceived happi-
ness have reduced sympathetic activation after exposure
to psychological stressors compared with those having
low levels of perceived happiness [4]. A recent study has
also indicated that perceived happiness is negatively
correlated with depression and anxiety [5]. Therefore,
perceived happiness level is involved in both psycho-
logical and physiological well-being. The neurobiologi-
cal mechanism that explains these positive effects of
happiness on psychological and physiological well-being
remains obscure. The medial prefrontal cortex (MPFC)
is one of the brain regions that may be involved in psy-
chological and physiological wellness. It has been shown
that electrical stimulation of the MPFC has an antide-
pressant effect by increasing synaptic availability of se-
rotonin [6], suggesting that MPFC maintains positive
mood states. From this viewpoint, it is suggested that
individuals with high levels of perceived happiness have
stronger MPFC activity and stronger positive emotion
evocation than individuals with low levels of perceived
happiness upon exposure to positive emotional stimuli.
To test this hypothesis, participants in this study were
required to watch films featuring people that they con-
sidered attractive, and we simultaneously recorded their
brain activity using 15O-water positron emission tomo-
graphy (PET) during various mood states.
2.1. Participants
We recruited 18 healthy right-handed male volunteers
(age range, 20 - 29 years). None of the participants had
M. Matsunaga et al. / Natural Science 3 (2011) 723-727
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chronic illness and none were taking medications known
to affect immunity. Only men were included to avoid
gender-related endocrine system and immune variations
caused by the female menstrual cycle. To screen indi-
viduals with higher or lower levels of perceived happi-
ness, we requested them to use the Japanese version of
the subjective happiness scale (JSHS) [5]. The JSHS is a
4-item scale that measures relatively stable perceived
happiness. Internal consistency, test-retest reliability,
convergent validity, and discriminant validity of the
JSHS have been confirmed [5]. Results of this screening
investigation indicate that the mean JSHS score for the
participants was 4.83 with a standard deviation (SD) of
0.9, similar to those reported earlier [5]. According to
the mean participant JSHS score, we designated partici-
pants with scores >5.0 as higher happiness respondents
(n = 9) and those <4.9 as lower happiness respondents (n
= 9). The participants were age-matched. All participants
signed informed consent forms prior to participating in
the study in accordance with university policy, and the
study was approved by the Kizawa Memorial Hospital
ethics committee.
2.2. Task Procedure
Each participant was instructed not to eat for 2 h be-
fore the scanning session but was allowed nonalcoholic
and caffeine-free fluids. Either an emotionally neutral
film (control film) or a film featuring people that the
participant considered attractive (positive film) was
viewed for 4 min on a 15-inch display positioned ap-
proximately 60 cm from the participants. PET scanning
(duration, 60 s) was performed during the first 2 - 3 min
of the screening. To obtain reliable PET data, each par-
ticipant was assigned 2 positive and 2 control films and
4 PET scans were obtained per participant. The control
film was a TV news program that featured a newscaster
that the participants did not consider particularly attrac-
tive. The participants watched the edited control and
positive films for the first time at the time of the experi-
ment. The emotional valence of the films had been pre-
viously evaluated [7]. The order of the 2 film types was
randomized across participants. The detailed PET pro-
cedure was described previously [7].
2.3. Image Acquisition by PET, Image
Processing, and Analysis
During each film-watching period, the distribution of
regional cerebral blood flow (rCBF) was measured using
an Advance NXi PET scanner (GE Healthcare Life Sci-
ences, Little Chalfont, England) operating in high-sensi-
tivity 3-dimensional mode [7]. SPM99 software [8] im-
plemented in Matlab (version 6.1; Mathworks, Sherborn,
MA) was used for spatial preprocessing and statistical
analyses as described previously [7]. To clarify signifi-
cant regional changes within groups (high vs. low) dur-
ing the positive condition, differences between the 2
groups were analyzed by subtracting the images of the
low happiness group from the images of the high happi-
ness group (each obtained by subtracting the control
condition images from those obtained during the positive
condition). The effects at each voxel were estimated
using a general linear model. Voxel values for each con-
trast yielded a statistical parametric map of the t-statistic
(SPM t), which was subsequently transformed to a unit
normal distribution (SPM z). The peak voxel value sig-
nificance thresholds were set at p < 0.001 (uncorrected)
and the cluster significance thresholds were set at 15
Further, to examine the association between brain ac-
tivity reflected by the rCBF and positive mood, we cre-
ated statistical parametric maps to identify the brain re-
gions that were activated in synchrony with the positive
mood changes using the high happiness group data. For
these maps, the covariates option was selected, generat-
ing regression analyses that tested the linear relationship
between rCBF and positive mood, yielding a z score at
each voxel. We entered the value changes obtained in
the positive mood obtained by subtracting the value be-
fore watching a film from the value after watching a film
as covariates. For covariate analysis, the statistical
threshold was set at p < 0.0001 (uncorrected) for height
and clusters including >20 contiguous voxels were re-
ported. For ease of discussion, we refer to our findings in
terms of significant “correlations,” although the analysis
formally involved linear regression rather than correla-
tion assessment. After voxel-wise regression analysis,
the MPFC value was extracted using SPM99, and the
Pearson correlation coefficient was computed between
the MPFC response and the positive mood change. Both
control and positive conditions (2 × 9 data points) were
used in both the voxel-wise regression analysis and the
Pearson correlation coefficient computation.
2.4. Statistical Analyses
The positive mood before and after film watching was
compared using 3-way analysis of variance (ANOVA)
(group [high vs. low] × condition [control vs. positive] ×
period [before vs. after]), followed by paired t-tests. This
index was measured twice for each condition; thus, sta-
tistical analyses were conducted among participants after
each participant’s average was calculated.
Subtraction of the low happiness from the high hap-
M. Matsunaga et al. / Natural Science 3 (2011) 723-727
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piness group data revealed significant increases in the
rCBF of the MPFC (Brodmann area 9; x, y, z = –2, 58,
30), dorsal striatum (x, y, z, = –16, 10, –4), insula (x, y,
z = –36, 10, 0), and supplementary motor area (SMA; x,
y, z = –14, 8, 64) (Figure 1). With regard to the positive
mood, the ANOVA identified significant interactions of
group (high vs. low) × condition (control vs. positive) ×
period (before vs. after) (F [1,32] = 5.75, p < 0.05; Fig-
ure 2). Further statistical analyses indicated that watch-
ing the positive film significantly elevated the positive
mood in both groups: high: t(8) = 5.53, p < 0.01; low: t(8)
= –3.41, p < 0.01 (Figure 2). However, the positive
mood score after watching the positive film was higher
in the high happiness group than in the low happiness
group: t (8) = 3.46, p < 0.01 (Figure 2). We then ana-
lyzed the correlation between change in positive mood
and rCBF: positive correlations were identified in sev-
eral brain regions, including the MPFC (x, y, z = –2, 56,
38). The MPFC value, which was activated greatly in the
high happiness group, was then extracted and the Pear-
son correlation coefficient between the MPFC response
and the positive mood change was computed: r (18) =
0.51, p < 0.05 (Figure 3).
We hypothesized that the MPFC may be strongly ac-
tivated in individuals with high levels of perceived hap-
piness and that strong positive emotions may be evoked
upon sight of a favorite person compared to individuals
with low levels of perceived happiness. As expected, this
Figure 1. Brain regions activated by the
positive films in the high happiness group
as identified by PET and by subtracting
the low happiness group values from the
high happiness group values (p < 0.001,
uncorrected). PET: positron emission to-
mography; MPFC: medial prefrontal cor-
tex; SMA: supplementary motor area.
Figure 2. Change in positive mood state
after watching the films. p < 0.01 vs.
before watching by paired t-test. ††p <
0.01 vs. after watching the positive film in
the low happiness group by paired t-test.
Figure 3. SPM99 covariate analysis results (p < 0.0001, un-
corrected) showing a positive correlation between change in
positive mood and rCBF in the MPFC; scatterplot showing
MPFC activity and positive mood change from baseline to
after film screening (r(18) = 0.51, p < 0.05). rCBF: regional
cerebral blood flow; MPFC: medial prefrontal cortex.
study showed that the high happiness group had a
greater degree of MPFC activation. Moreover, strong
positive emotions were evoked in participants in this
group compared to participants in the low happiness
group when the participants looked at a favorite person.
Covariate analysis indicated that MPFC activation was
positively correlated with positive mood increases.
These results show that perceived happiness level is as-
sociated with positive emotion evocation via MPFC
function. Thus, individuals with high levels of perceived
happiness may maintain psychological well-being via
MPFC function. In addition, MPFC can control auto-
M. Matsunaga et al. / Natural Science 3 (2011) 723-727
Copyright © 2011 SciRes. Openly accessible at http://www.scirp.org/journal/NS/
nomic nervous system activity via brain autonomic cen-
ters such as the hypothalamus and midbrain through
direct neural projections [9]. Thus, it is possible that
reduced sympathetic activation in individuals with high
levels of perceived happiness after exposure to psycho-
social stressors [4] will also be attributable to the MPFC
function. A well-functioning MPFC may mediate the
association between perceived happiness and health and
Happiness is a positive feeling characterized by con-
tentment, satisfaction, joy, pleasure, or love. Dopamine
plays an important role in the expression of positive
emotions [10-12]. The dopaminergic network within the
brain, which projects to the prefrontal cortex and stria-
tum from the midbrain region, is known as the “brain
reward system” [10,11], and our results indicated that
the reward-related brain regions including the dorsal
striatum were strongly activated in individuals with high
levels of perceived happiness. Findings have suggested
that dopaminergic function deficiency may be a possible
explanation for depression [13] and that antidepressant
treatment facilitated dopamine release in the nucleus
accumbens of a genetic animal model of depression [14].
Furthermore, activation of reward-related brain regions
can improve physiological functions including immune
functions [7]. Thus, brain dopaminergic function may be
a key factor in the positive effects of perceived happi-
ness levels.
The present study also indicated that activation of the
insula and SMA was higher in the high happiness group
than in the low happiness group when participants
looked at a favorite person. The insular cortex is in-
volved in the perception of signals arising from the body
and plays an important role in emotional experience
[15-17]. We have recently shown that parasympathetic
activity increases after an individual experiences positive
emotions and that activity of the insular cortex is associ-
ated with changes in peripheral autonomic activity [18].
Although the present study could not measure the pe-
ripheral autonomic activity during the task because of
technical limitations, it is possible that parasympathetic
activity was greater in the high happiness group than in
the low happiness group when positive emotions were
elicited, and the greater insula activity in the high hap-
piness group reflected this. Moreover, one study indi-
cated a positive correlation between SMA activity and
laughter/smiling; therefore, SMA activity reflects motor
activity associated with these actions [19]. The individu-
als with high levels of happiness probably smiled often
while watching the positive film compared with those
having low levels of happiness. Therefore, positive emo-
tion-related brain regions may have been highly stimu-
lated upon sight of a favorite person by participants of
the high happiness group compared with those of the
low happiness group.
Certain limitations of this study must be recognized.
Some reports have noted gender-related differences with
regard to perceived happiness level and physiological
reactivity [5,20], and we did not investigate the effect of
gender. Thus, the generalizability of the present findings
must be further tested using a larger sample size that
includes both male and female participants.
The findings of this study indicate that perceived hap-
piness level is associated with evocation of positive
emotions via MPFC function. High MPFC function in
individuals with high perceived happiness levels may
enhance psychological and physiological wellness.
This work was supported by Grant-in-Aid for Young Scientists (B)
from the Japan Society for the Promotion of Science (22700683 to
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