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Cooperation in Lovers: An fNIRS-Based Hyperscanning Study

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This study investigated interactive exchange in lovers and the associated interpersonal brain synchronization (IBS) using functional near-infrared spectroscopy (fNIRS)-based hyperscanning. Three types of female-male dyads, lovers, friends, and strangers, performed a cooperation task during which brain activity was recorded in right frontoparietal regions. We measured better cooperative behavior in lover dyads compared with friend and stranger dyads. Lover dyads demonstrated increased IBS in right superior frontal cortex, which also covaried with their task performance. Granger causality analyses in lover dyads revealed stronger directional synchronization from females to males than from males to females, suggesting different roles for females and males during cooperation. Our study refines the theoretical explanation of romantic interaction between lovers.
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Cooperation in Lovers: An fNIRS-Based
Hyperscanning Study
Yafeng Pan,
1
Xiaojun Cheng,
1
Zhenxin Zhang,
2
Xianchun Li,
1
*and Yi Hu
1
*
1
School of Psychology and Cognitive Science, Faculty of Education, East China Normal
University, Shanghai, People’s Republic of China
2
Department of Psychology, Zhejiang Normal University, Jinhua, People’s Republic of China
r r
Abstract: This study investigated interactive exchange in lovers and the associated interpersonal brain
synchronization (IBS) using functional near-infrared spectroscopy (fNIRS)-based hyperscanning. Three
types of female-male dyads, lovers, friends, and strangers, performed a cooperation task during which
brain activity was recorded in right frontoparietal regions. We measured better cooperative behavior in
lover dyads compared with friend and stranger dyads. Lover dyads demonstrated increased IBS in
right superior frontal cortex, which also covaried with their task performance. Granger causality analy-
ses in lover dyads revealed stronger directional synchronization from females to males than from
males to females, suggesting different roles for females and males during cooperation. Our study
refines the theoretical explanation of romantic interaction between lovers. Hum Brain Mapp 38:831–841,
2017.V
C2016 Wiley Periodicals, Inc.
Key words: cooperation; lovers; interpersonal brain synchronization; fNIRS; hyperscanning
r r
INTRODUCTION
Humans have a natural inclination to form bonds with
others, which is more evidenced for romantic relationships
(Acevedo et al., 2012; Fletcher et al., 2015). In this type of
relationship, people of both sexes have a very large
amount of social interactions, such as sharing positive life
events and receiving quality feedback (Gable et al., 2003,
2004). Their interactions, with the same goals in most cases
(Li et al., 2002; Li and Kenrick, 2006), set the stage for
some degree of overlap in their behaviors. In the current
study, we investigate how lovers interact with each other
and any associcated synchronous brain activity between
them.
According to the theory of attachment, individuals
develop mental representations of their relations with
parents, peers, lovers and so on (Furman et al., 2002,
2014). These representations are not fully congruent with
each other. Romantic relationships, compared to other
relationships, involve the integration of sexual, caregiving
and affiliative behavioral systems (Furman et al., 2014).
These behavioral systems provide rich opportunities for
lovers to cooperate (Ackerman and Kenrick, 2009; Schnei-
derman et al., 2012), examples include mutual touch
(Gallace and Spence, 2010), constructive problem-solving
(Assad et al., 2007), and emotion coordination (Randall
et al., 2013). Neurobiological studies have even shown that
when participants view pictures of a loved one, their
Additional Supporting Information may be found in the online
version of this article.
Contract grant sponsor: Peak Discipline Construction Project of Edu-
cation at East China Normal University; National Natural Science
Foundation of China; Contract grant number: 31371052 (to Y.H.)
Y. Pan and X. Cheng contributed equally to this study.
*Correspondence to: Yi Hu, School of Psychology and Cognitive
Science, East China Normal University, Shanghai, 200062, People’s
Republic of China. E-mail: yhu@psy.ecnu.edu.cn and Xianchun Li,
School of Psychology and Cognitive Science, East China Normal
University, Shanghai, 200062, People’s Republic of China. E-mail:
xcli@psy.ecnu.edu.cn
Received for publication 29 April 2016; Revised 30 August 2016;
Accepted 23 September 2016.
DOI: 10.1002/hbm.23421
Published online 4 October 2016 in Wiley Online Library
(wileyonlinelibrary.com)
rHuman Brain Mapping 38:831–841 (2017) r
V
C2016 Wiley Periodicals, Inc.
oxytocin levels surged (de Boer et al., 2012; Zeki, 2007).
Oxytocin is a hormone that plays a pivotal role in trust,
empathy, and cooperation (Kosfeld et al., 2005; Schneider-
man et al., 2012). These findings are suggestive of the
cooperative nature of romantic relationships.
Gender differences in cooperation between lovers can be
explained by established theories from psychology and
evolutionary biology. The self-construal theory suggests
that females are interdependent and males are indepen-
dent (Cross and Madson, 1997). Females are more sharing,
affiliative, and emotionally supportive than males. They
display greater levels of prosociality, such as empathy,
selflessness, and positive emotions (e.g., Cross and Mad-
son, 1997; Eckel and Grossman, 1998; Zakriski et al., 2005).
It seems that, in general, females are more romantically
submissive to males. However, there might be other possi-
bilities. From an evolutionary biology perspective, females
expend more physical and temporal resources in pregnan-
cy and offspring care compared to males. The female
tends to be relatively choosy regarding acceptable qualities
in potential mates and to be actively restricted in their
access to the opposite sex partners (Buss and Schmitt,
1993; Kenrick et al., 1990; Li et al., 2002; Perilloux et al.,
2008). Males, on the other hand, may use more flexible tac-
tics (e.g., flaunting) to demonstrate acceptable mate-value
(Geary et al., 2004; Griskevicius et al., 2006) and thus
might be more capable of humoring females.
We asked two partners in a lover dyad to perform a
cooperative task (Baker et al., 2016; Cheng et al., 2015; Cui
et al., 2012). The lover dyad tried their best to simulta-
neously make quick responses to a stimulus. The quality of
their performance was defined by the difference and vari-
ability between their response times. A small difference
and less variability implied better cooperation (Funane
et al., 2011; Vesper et al., 2011). During the task, we simul-
taneiously recorded brain activities from both partners,
which is known as the “hyperscannning.” Hyperscanning
can be used with fMRI (e.g., Chiu et al., 2008; Li et al.,
2009), EEG (e.g., Lindenberger et al., 2009), and fNIRS (e.g.,
Cheng et al., 2015; Jiang et al., 2015; Tang et al., 2016). Pre-
vious studies using the hyperscanning technique during
studies of cooperation found interpersonal brain synchroni-
zation (IBS) in right centroparietal regions (Dumas et al.,
2010) and prefrontal cortex (McCabe et al., 2001).
Hyperscanning has been used to investigate neural links
between lovers. Specifically, an fMRI study found that
affective facial communication in romantic partners eli-
cited activations in the same cerebral networks, such
as anterior temporal, insular, and somato-motor brain
regions (Anders et al., 2011). A recent EEG study found
that romantic kissing in lovers induced intra- and inter-
brain synchronization in the theta-alpha band (M
uller
and Lindenberger, 2014). We adopted the fNIRS-based
hyperscanning technique. The fNIRS device is more tol-
erant of motor artifacts and acheives temporal and spa-
tial resolutions that are comparable to fMRI and EEG. A
single fNIRS device can be divided for hyperscanning
experiments by using half of the channels for each par-
ticipant (Cheng et al., 2015; Cui et al., 2012). Therefore,
thefNIRSset-upcanresolvetheissueofvariablesensi-
tivities from different devices.
In sum, this study explored interactive exchange between
lovers through fNIRS-based hyperscanning. Based on the
more interactive experiences and the cooperative nature of
romantic relationships, we expected that lover dyads would
outperform friend and stranger dyads on the cooperative
task. Also, we anticipated that better performance would be
accompanied by increased IBS between the two partners.
Previous studies have found that right frontoparietal cortex
is associated with cooperation and reciprocal interactions
(Decety et al., 2004). Moreover, a right-lateralized frontopar-
ietal mirror-neuron network was shown to be involved
with social understanding (e.g., understand the emotions
and actions of others, Gallese et al., 2004; Iacoboni et al.,
2005) and was considered as the basis for bridging the self-
other gap during interaction (Uddin et al., 2007). Based on
these studies, we defined the region-of-interest for the pre-
sent study to be right frontoparietal area. Meanwhile, we
examined gender differences at the level of behavior and
brain activity, with the goal of providing evidence for either
self-construal theory or the evolutionary biological theory of
heterosextual cooperation.
METHOD
Participants
Ninety-eight adults (49 dyads, age: 21.07 61.85 yrs) par-
ticipated in the study. They were all male–female dyads,
which included 17 lover dyads, 16 friend dyads, and 16
stranger dyads. Lover dyads as well as friend dyads had
been acquainted before the experiment, and these two
types of dyads did not differ in duration of acquaintance
(21.01 65.08 vs. 15.75 63.41 months, t
(31)
51.23, P50.23,
Cohen’s d50.32). The lover dyads reported that they were
intensely in love (duration of “being in love”: M515.15
months, range 52–36 months). Each participant signed
informed consent before the experiment and was paid ¥ 20
for participation. The University Committee on Human
Research Protection of East China Normal University
approved study procedure.
Tasks and Procedures
Two participants in a dyad sat side-by-side, separated
by a board and in front of a shared computer display
(Fig. 1A). The procedure consisted of Rest 1 (30 s), Task
Block 1 (150 s), Rest 2 (30 s), Task Block 2 (150 s), and
Rest 3 (30 s) (Fig. 1B). For each task block, participants
needed to complete 20 trials. Within each trial (Fig. 1C), a
hollow gray circle (0.6 – 1.5 s) was presented first, followed
by a green signal. Upon seeing the signal, participants
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used their right index fingers to press the key simulta-
neously. The participant on the left (participant #1) used
the “1” key on a keyboard, and the participant on the right
(participant #2) used the “2” key on the other keyboard.
To maintain participants’ attention and increase cooper-
ative behaviors, we set a threshold (T) for a trial for which
they would get a winning point:
T51
8RT11RT2ðÞ
where RT1 and RT2 were the response times of participant
#1 and participant #2, respectively. The parameter 1/8 was
chosen to maintain a reasonable difficulty level (Baker
et al., 2016; Cheng et al., 2015; Cui et al., 2012). For each
dyad, if the time difference was smaller than their thresh-
old, both won one point; otherwise, they lost one point.
After key-pressings, a feedback screen (4 s) appeared.
The feedback consisted of the following information: (1)
win or lose; (2) cumulative points; (3) who was faster
(“1”) or slower (“2”). This information aided participants
in adjusting their responses to maximize points. No verbal
or physical communication was allowed. After the feed-
back, there was a blank screen (i.e., the intertrial interval)
lasting 2 s.
Subjective Measurements
We collected each participant’s attitudes towards her/
his partner and the experiment, these information includ-
ed: (1) trustworthiness for others in their daily life (pre-
experiment); (2) satisfaction for her/his own performance
(post-experiment); (3) cooperativeness during the coopera-
tion (post-experiment); (4) pleasantness while cooperating
(post-experiment); (5) concentration during tasks (post-
experiment); (6) favorability for the partner (pre- and post-
experiment). Participants used a 7-point Likert scale,
which ranged from 1 (“not very much”) to 7 (“very
Figure 1.
Experimental design. (A) Experimental setup. (B) Task design. There were two task blocks, each
consisting of 20 trials. (C) Trial design. Events and time flow in a trial. (D) Optode probe set.
The set was placed on the right frontoparietal cortices. [Color figure can be viewed at wileyonli-
nelibrary.com]
rCooperation in Lovers r
r833 r
much”), for all ratings. No discussion was allowed while
rating.
Data Acquisition
An ETG-4000 optical topography system (Hitachi Medi-
cal Corporation, Japan) was used to record the oxyhemo-
globin (HbO) and deoxyhemoglobin (HbR) concentrations
for each dyad. The absorption of near infrared light (wave-
lengths: 695 and 830 nm) was measured at a sampling rate
of 10 Hz. The optode probe set was placed over partici-
pants’ right frontoparietal regions (Fig. 1D), based on pre-
vious work showing cooperative exchange involved right
frontal and parietal regions (Decety et al., 2004).
Two 3 35 optode probe sets (eight emitters and seven
detectors, 3 cm optode separation) were used. Each set
consists of 22 measurement channels (CHs). The center of
the middle probe set row was placed at C4, according to
the 10/20 international system. The middle probe set col-
umn was placed along the sagittal reference curve. The
virtual registration method was used to determine the cor-
respondence between the NIRS CHs and the measured
points on the cerebral cortex (Singh et al., 2005; Tsuzuki
et al., 2007).
Data Analysis
Behavior performance
For each participant dyad, response times (RTs), and
winning trials were recorded. Because there were some
outliers in the data, the median and median absolute devi-
ation of response times (median-RT, mad-RT) were calcu-
lated among all trials in each participant. Outliers were
identified by calculating an interval spanning over the
mean 63 SD. We also analyzed the median and median
absolute deviation of the difference of response times
(median-DRT and mad-DRT) between the two participants
in a dyad, similar to procedures used in previous studies
(Funane et al., 2011; Vesper et al., 2011). To quantify par-
ticipant performance and index the quality of cooperation,
we calculated the percentage of winning trials (PWT;
Cheng et al., 2015; Cui et al., 2012).
Nonparametric Wilcoxon tests were used on the
median-RT, mad-RT, median-DRT, and mad-RT, because
the data were not normally distributed. The PWT was dis-
tributed normally, so we applied a two-way ANOVA,
with factors of Group (lover, friend, stranger) by Task
Block (blocks 1, 2). Finally, we used a Bonferroni correc-
tion to account for multiple comparisons.
Interpersonal brain synchronization (IBS)
Because the HbO signal has been demonstrated to be
most sensitive to changes in cerebral blood flow during
fNIRS measurements (Cui et al., 2012; Hoshi, 2007), we
focused on the HbO time series. However, HbR time series
were also analyzed (see Supporting Information).
During preprocessing, the initial and ending periods
(Rest 1 and Rest 3, respectively) of the task were removed.
A line of evidence mentioned that the fNIRS can measure
both global (i.e., systemic components which are not task-
specific activity) and cortical blood oxygen level dependent
(BOLD) activities (Ferrari and Quaresima, 2012; Kirilina
et al., 2012), Therefore, we first used a principal component
spatial filter algorithm (i.e., PCA approach using Gaussian
spatial filtering) to remove the global components (Zhang
et al., 2016). Wavelet transform coherence (WTC) was then
used to assess the relationship between HbO time series for
each dyad (for more details see Grinsted et al., 2004). Based
on WTC analyses of two time series generated by each par-
ticipant dyad, we focused on the frequency band between
3.2 s and 12.8 s (i.e., 0.08 – 0.31 Hz) that was more sensitive
to our task (Fig. 2). Specifically, this frequency band
includes the period of the single trial (7s)inthecoopera-
tion task indicating that this coherence increase is task-
related. The selection of frequency band was also in accor-
dance with previous studies using the same paradigm
(Baker et al., 2016; Cheng et al., 2015; Cui et al., 2012).
Focusing on this frequency band enabled removal of high-
and low-frequency artificial noises, such as those related to
cardiac pulsation (1Hz).
For each pair of CHs between two participants, the aver-
age cross-brain coherence, or IBS, was calculated in task
Figure 2.
Frequency band of interest. Interpersonal brain synchronization
(IBS) indicated by wavelet transform coherence (WTC). The
coherence based on raw HbO signal from channel 20 (CH20) in
a representative pair of lovers. The red border represents the
frequency band of interest (3.2 s – 12.8 s), indicating when the
task was carried out. The color bar denotes the value of WTC
(1 5highest coherence, 0 5lowest coherence). [Color figure
can be viewed at wileyonlinelibrary.com]
rPan et al. r
r834 r
blocks and resting period. We defined IBS as the mean of
coherence in two task blocks minus the coherence during
the inter-block rest period (Rest 2):
IBS51
2IBSblock 11IBSblock 2
ðÞ2IBSrest 2
We converted IBS values to Fisher z-statistics and then cal-
culated a one-sample t-test with false discovery rate (FDR)
correction across all CHs (P<0.05). We generated a t-map
of IBS and smoothed it using the spline method. If a chan-
nel was found with significant IBS, a one-way ANOVA
was conducted on that IBS with the factor of Group. Bon-
ferroni correction was used to account for post hoc multi-
ple comparisons.
Directional coupling
To estimate the direction of synchronization for CHs
that exhibited significant IBS, Granger causality analyses
(GCA) were conducted (see more details in Barnett and
Seth, 2014; Im et al., 2010). GCA uses vector autoregressive
models to measure the causal relationship between time
series in brain data. Our GCA was based on PCA-
corrected signals during the task periods. The pairwise-
conditional Granger-causality (G-causality) of both partici-
pant directions (i.e., from females to males; from males to
females) was calculated. Then, one-sample t-tests were
used to examine whether each direction differed from
zero, and two-sample t-tests were used to compare differ-
ences between two directions.
Subjective measurements
A series of two-way ANOVAs were conducted to
estimate the effects of Group and Gender on participants’
ratings of their (1) trustworthiness, (2) satisfaction, (3)
cooperativeness, (4) pleasantness, and (5) concentration.
One three-way ANOVA was carried out on partner favor-
ability with the factors of Group, Gender, and Time (pre-
vs. post-experiment). We conducted follow-up t-tests with
Bonferroni corrections when necessary.
RESULTS
Behavioral Performance
For individual behavioral data, Wilcoxon tests on
median-RT showed that lover dyads responded faster than
stranger dyads (Bonferroni corrected,P<0.05; see Sup-
porting Information Table S1). Similar analyses on mad-RT
revealed that responses from lover and friend dyads were
less variable than stranger dyads responses (Bonferroni
corrected,Ps<0.05; see Supporting Information Table S2).
Additionally, we explored gender differences on median-
RT and mad-RT between these three groups. Wilcoxon
tests on median-RT showed that males responded slower
than females in the lover dyads (P<0.05), but not in
friend and stranger dyads (Ps>0.05; see Supporting Infor-
mation, Table S1). No other significant effect was found.
We tested for joint cooperation by using Wilcoxon tests
on median-DRT. These tests showed significant group dif-
ferences between lover and friend dyads (P<0.05), and
between lover and stranger dyads (P<0.05; Fig. 3A).
These differences indicate that median-DRT in lover dyads
was smaller than friend and stranger dyads. Similar analy-
ses on mad-DRT confirmed that mad-DRT in lover dyads
was smaller than friend and stranger dyads (Ps<0.05;
Fig. 3B).
The analysis of PWT (ANOVA with factors of Group
and Task Block) yielded statistical significance only for
Figure 3.
Cooperation performance. (A) The median of difference of response time (median-DRT).
(B) The median absolute deviation of difference of response time (mad-DRT). * P<0.05, after
correction. Error bars represent standard errors.
rCooperation in Lovers r
r835 r
Task Block (F
(1,46)
524.35, P<0.001, h2
p50.35) with the
higher PWT in block 2 among all groups (Ps<0.05; see
Supporting Information, Table S3 and Fig. S1). These find-
ings confirm that all participants performed the coopera-
tion task as instructed.
Interpersonal Brain Synchronization (IBS)
A series of one-sample t-test analyses of IBS in lover
dyads found significant IBS at CH19 (t
(16)
52.40, P<0.05,
Cohen’s d50.82) and CH20 (t
(16)
54.25, P<0.001,
Cohen’s d51.46). However, only IBS at CH20 survived
after FDR correction (P<0.05; Fig. 4A). CH20 was rough-
ly located in the right superior frontal cortex (r-SFC;
Tzourio-Mazoyer et al., 2002). In contrast, no significant
IBS was found in friend or stranger dyads. A one-way
ANOVA analysis demonstrated that IBS at CH20 was
affected by Group, (F
(2,46)
53.91, P<0.05, h2
p50.14). The
post hoc tests revealed that IBS in lovers was significantly
greater than that in friends and strangers (P<0.05;
Fig. 4B).
The IBS-Behavior Relation
Pearson correlation analyses were conducted on the sig-
nificant IBS at CH20 and behavior indices (e.g., DRT,
PWT). IBS and median-DRT were correlated (Fig. 5A,
r520.50, P<0.05), indicating that the IBS found in lover
dyads was associated with their cooperative performance.
However, similar correlations were not statistically signifi-
cant in friends or strangers (Ps>0.1).
We also calculated the change in IBS between task
blocks by subtracting the coherence value in task block 1
from that in task block 2, IBS
block 2 – block 1
, based on previ-
ous work (Cheng et al., 2015). The correlation between
IBS
block 2 – block 1
and the increase of winning trials from
block 1 to block 2, PWT
block 2 – block 1
, was significant (Fig.
5B, r50.56, P<0.05). In contrast, this relationship was
not significant in friend and stranger dyads (Ps>0.1).
Directional Coupling
To determine the direction of IBS at CH20, we con-
ducted one-sample t-tests on the mean G-causality. For
Figure 4.
Interpersonal brain synchronization (IBS). (A) One-sample t-test
map of IBS. (B) Upper graph: one-way ANOVA results of the
IBS to identify group differences. Lower graph: The amplitude of
synchronization at channel 20 (CH20). Note that only in lover
dyads, a significant IBS at CH20 was found after FDR correction.
Synchronization in lover dyads is higher than that in other dyads.
*P<0.05, after correction. Error bars represent standard
errors. [Color figure can be viewed at wileyonlinelibrary.com]
rPan et al. r
r836 r
lover dyads, both directions demonstrated significant
increases in the mean G-causality relative to zero: from
females to males (t
(16)
57.02, P<0.001, Cohen’s d52.41)
and from male to female (t
(16)
54.23, P<0.001, Cohen’s
d51.45; Fig. 6A). A two-sample t-test revealed that mean
G-causality from females to males was significantly larger
than from males to females (t
(16)
52.97, P<0.01, Cohen’s
d50.91; Fig. 6B). In contrast, no significant G-causality in
either direction or difference between the two directions
was found for the other dyads (Ps>0.05).
Subjective Measurements
The results of two-way ANOVAs showed no significant
effect of Group in evaluations of trustworthiness and con-
centration. However, the effect of Group was significant
on self-rated pleasantness (F
(2,95)
58.62, P<0.001,
h2
p50.08), satisfaction (F
(2,95)
55.71, P<0.01, h2
p50.06),
and cooperativeness (F
(2,95)
510.20, P<0.001, h2
p50.10).
Post hoc tests demonstrated that lover dyads felt more
pleasant and more satisfied than stranger dyads did
(Ps<0.05), but not than the friend dyads did (Ps>0.05).
Lovers felt more cooperative than friend and stranger
dyads (Ps<0.05). To address the potential contribution of
these subjective experiences to IBS, we examined whether
the self-rated pleasantness, satisfaction or cooperativeness
correlated with IBS. None of these correlations survived
(Ps>0.1).
Finally, we conducted a three-way ANOVA on partner
favorability that showed effects of Time (F
(1,95)
546.29, P
<0.001, h2
p50.21) and an interaction between Time and
Group (F
(2,95)
58.11, P<0.001, h2
p50.08). Further analyses
showed that friend and stranger dyads developed more
favorable impressions of their partners from the beginning
to the end of the experiment (Ps<0.01), while lover dyads
did not (P>0.1). The descriptive statistics can be found in
Supporting Information, Table S4.
DISCUSSION
To our knowledge, this is the first fNIRS-based hyper-
scanning study exploring interactive exchange in lovers.
Behavioral results showed that response time differences
between lover dyads were smaller and less variable than
friend and stranger dyads, indicating better cooperation
among lovers. More importantly, fNIRS results showed
interpersonal brain synchronization (IBS) only for lover
dyads. The IBS obtained in lover dyads was also found to
correlate with their task performance.
We found IBS in lover dyads using a task involving
interactive exchange in the form of simultaneously press-
ing keys to maximize joint performance. Our results are
consistent with IBS findings in other interactive activities,
such as game playing (Liu et al., 2016), button pressing
(Funane et al., 2011), and jointly acting (Dommer et al.,
2012). IBS might be accounted for by the familiarity lovers
have with each other or by their emotional involvement
with each other. However, we think these factors are
unlikely based on the following evidence. First, we
observed no significant IBS in friend dyads, who had a
similar duration of acquaintance as lover dyads. Second,
although lover-dyads reported more pleasantness during
the interactive exchange, our analyses suggested that it
might not affect the IBS (see Subjective Measurements in
the Results part). Thus, we argue that IBS found in lover
dyads arises from working together on the task, echoing
Figure 5.
IBS-behavior correlation in lover dyads. Correlations (A) between the IBS at CH20 and median-
DRT, (B) between IBS change at CH20 (IBS
block 2 – block 1
) and percentage of winning trials
change (PWT
block 2 – block 1
).
rCooperation in Lovers r
r837 r
the proposal that “significant others” trigger response
facilitation and therefore lead to two interactive partners
“being in tune” (Byrne, 2005). The cooperative task might
also recruit other cognitive processes, such as shared emo-
tions and social intentions, in addition to joint actions.
Whether our findings can generalize to these modalities is
a direction for future research.
We found IBS in the right superior frontal cortex
(r-SFC). Previous functional brain imaging studies reported
the engagement of superior frontal gyrus/intraparietal sul-
cus while viewing a lover’s photograph (Bartels and Zeki,
2000, 2004; Xu et al., 2011) and medial orbitofrontal cortex/
parietal lobes while thinking of their romantic partner (Xu
et al., 2012). A recent study even found that functional
resting-state connectivity in the frontoparietal network was
significantly enhanced for the “in-love” group (Song et al.,
2015). The function of r-SFC has been intensely discussed in
the literature: it has been implicated in implicit understand-
ing of others’ action (Hari and Kujala, 2009), response
inhibition (Dziobek et al., 2012), working memory (du Bois-
gueheneuc et al., 2006), and self-awareness (Goldberg et al.,
2006). The role of r-SFC identified here offers support for
the theory of mind hypothesis (Cui et al., 2012; Yang et al.,
2015), as our cooperation game required understanding,
modeling, and predicting partner behavior. Certainly, the
exact meaning of the IBS at superior frontal cortex (SFC) is
a direction for future research.
We observed similarities and differences between our
findings and two recent studies using fNIRS-based hyper-
scanning. Cui et al. (2012) found IBS at the r-SFC for the
cooperation of 11 participant-dyads, but the gender of the
two partners was not under consideration. In a recent
study that controlled for gender, Cheng et al. (2015)
revealed IBS at the frontopolar cortex, orbitofrontal cortex,
and left dorsolateral prefrontal cortex for female-male
dyads, but not for female-female dyads and male-male
dyads. The fNIRS optode patch was placed mostly over
the prefrontal cortex, and the two partners were unac-
quainted with each other before the experiment. By con-
trast, our study relied on the a priori hypothesis that right
frontoparietal brain areas likely underlay social under-
standing and interactive exchange between partners.
We found gender differences in lover dyads: males
tended to respond more slowly to cues. The slower
response suggests that males needed extra time to adapt
their responses to females’ responses. In agreement with
our finding, a recent study found that when judging the
degree of romance in sentences, males responded more
slowly compared to females. The authors posit that males
may use more cognitive effort to perceive romance (Yin
et al., 2013). These findings support different roles for
females and males in romantic relationships.
Our GCA results for lover dyads further showed that
the direction of IBS from females to males was stronger
than from males to females, implying that the primary
information flow was from females to males. Previous
studies showed IBS directional differences for partners in
relationships as gesturer-guesser (Schippers et al., 2010),
model-imitator (Holper et al., 2012), and leader-follower
(Jiang et al., 2015). Specifically, the brain activity in the
gesturer predicted that of the guesser (Schippers et al.,
2010), the brain activity of the model caused that of the
imitator (Holper et al., 2012), and there was a more impor-
tant role for the leader compared to the follower (Jiang
et al., 2015). In our study, females might “lead” the activi-
ty and “send” information to males, who “receive” the
information and play the “follower” role. Results from
Granger causality analyses highlight the important role of
dynamic social interactions in lovers’ cooperation (Schil-
bach et al., 2013).
Gender differences found for lover dyads tends to sup-
port the evolutionary biological perspective that the male
is more capable of going along with females’ behavior
(Griskevicius et al., 2006; Hyde, 2014). We note that our
participants are mostly undergraduate university students.
Figure 6.
Directional coupling in lover dyads. (A) The G-causality was
analyzed on two directions (from males to females, from females
to males). Significant G-causality was indicated by the solid-lines
(thresholded at P<0.001). (B) Mean G-causalities in both direc-
tions were illustrated in the bar graphs. The mean causality
from females to males (indicated by red color) was significantly
higher than that from male to female (indicated by blue color).
**P<0.01. Error bars represent standard errors. [Color figure
can be viewed at wileyonlinelibrary.com]
rPan et al. r
r838 r
They are in the early stages of the romantic relationship,
during which males exert themselves, display acceptable
attributes, and demonstrate the ability to achieve sexual
access. As such, the examination of gender differences in
lovers should consider more factors, such as relationship
stage (Kenrick et al., 1990), attachment style (Furman
et al., 2002), and affiliation (Furman et al., 2014), to name a
few. In addition, studies have shown that in situations
involving prosocial behaviors, males are expected to
undertake the roles of high status and power, and thus
were more agentic and dominant than females (e.g., Eagly,
2009). Further investigation is needed to elaborate the gen-
der differences in romantic lovers during interactive
exchange.
Investigation of IBS using two-person interactions is a
promising yet nascent field, and it could provide insight
into higher cognitive functions, such as cooperation and
communication. However, fNIRS faces some analytic chal-
lenges. First, the spontaneous oscillations of blood flow
(i.e., Mayer waves, 0.1 Hz), which might contaminate the
task-related brain activities (Lloyd-Fox et al., 2010; Scholk-
mann et al., 2014), were included in our frequency of inter-
est (0.08–0.31 Hz). Consequently, we carried out a parallel
IBS analysis in the frequency band of 0.09–0.11 Hz, but no
significant group difference was detected (see Supporting
Information, Fig. S2). Such physiological process therefore
should have equal impact on fNIRS responses among all
groups and cannot explain our finding of increased IBS
only in the lover dyads. Second, fNIRS signals were con-
taminated with global systemic components, which are not
task-specific, such as the scalp blood flow and changes in
blood pressure. Therefore, we used a PCA approach that
included Gaussian spatial filtering to remove the global
systemic components (Zhang et al., 2016), although such
signals cannot be filtered out completely. Third, we
detected the primary components of IBS based on the
HbO measurement, and we cannot exclude the possibility
of additional useful information in the HbR signal. Previ-
ous studies have shown that HbO is more influenced by
scalp blood flow and HbR is more related to neurovascu-
lar coupling (Ou et al., 2009; Zhang et al., 2016). Therefore,
we also analyzed the HbR time series and found a similar
effect at the r-SFC (see Supporting Information, Fig. S3).
Because fNIRS signals might suffer from various con-
founding contaminants such as physiological processes
and global systemic effects, future studies could (1) collect
physiological responses, and (2) analyze both HbO and
HbR concentrations to get a full picture about measured
brain activity.
Limitations of this study are important to note. First, the
optode probe set of NIRS only covered the right frontopar-
ietal regions of the brain, leaving other regions unex-
plored. In a previous study of cooperative performance,
IBS was also found at the left inferior parietal lobule and
the occipital cortex (Egetemeir et al., 2011). The roles of
these brain regions could be examined by measuring from
the entire brain. Second, close personal relationships are
found to be closely related to motivation and reward brain
systems (Acevedo et al., 2012; Aron et al., 2005), and the
relevant brain structures are mostly subcortical. These sub-
cortical structures could be investigated by using fMRI-
based techniques. Third, we cannot dismiss the potential
effects of motivational state on the establishment of IBS,
since motivation plays an important role during the social
interactions (Canessa et al., 2012). Future studies could
manipulate or control participant’s motivational state and
explore the relationship between motivation and brain
activity.
In summary, we demonstrated that cooperative behavior
between lover dyads was better than friend and stranger
pairs and identified IBS in the right superior frontal cortex.
Our findings support the theory that there are distinctive
mental representations developed for individuals in rela-
tionships with others. Performance differences between
partners and the direction of IBS suggest a leading/affilia-
tive role for females/males in romantic relationships, pri-
marily supporting theories from evolutionary biology. Our
study advances the understanding of the unique brain sig-
nature for lovers’ interactions and potentially provides
insights in the evolution of human love.
ACKNOWLEDGMENTS
Authors thank Dr. Kimberlee D’Ardenne from the Depart-
ment of Psychology at Arizona State University for her
wonderful suggestions and grammar corrections. Authors
thank Yue Yang and Guowei Chen for their technical
assistance with the fNIRS hyperscanning. Authors thank
Qun Ye and Lili Zheng for their assistance in data acquisi-
tion and entry.
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rCooperation in Lovers r
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... Studies have consistently found that better cooperative interactions between individuals are associated with higher IBS [5,7,8]. Indeed, the accumulated hyperscanning research has reported that higher levels of IBS in the frontopolar cortex (FPC), orbitofrontal cortex (OFC), dorsolateral prefrontal cortex (DLPFC), superior frontal cortex (SFC), superior temporal gyrus (STG), and temporoparietal junction (TPJ) were associated with higher task performance during goal-oriented cooperative interactions [7,[12][13][14][15][16][17][18]. For instance, IBS in the FPC, which has a role in social interaction [19], tended to increase with increasing task performance during cooperation [12]. ...
... Factors related to the interacting partners include individual characteristics (i.e., age, gender) and their interpersonal relationship [23]. For example, Pan et al. [15] reported a significant increase in IBS in the r-SFC for dyads composed of lovers compared to male-female friends or stranger dyads. IBS in the TPJ and frontal cortex has been reported in studies of parent-child cooperative interactions [24]. ...
... Regions of interest (ROI) were created by the fNIRS optodes' location decider (fOLD) [35] and NIRS-SPM toolboxes in MATLAB. ROIs were grouped as follows: (1) left frontal lobe: CH 2, 3, 4, 5, 6, 7, 8, 9, 10, and 11; (2) right frontal lobe: 13,14,15,16,17,18,19,20 We assessed the anatomical positions of optodes and channels (CHs) on a standardized 3D head with Nz (nasion), Iz (Inion), AL (left preauricular point), AR (right preauricular point), and Cz (central zero) as referential points. Then, the NIRS_SPM software (http: //www.nitrc.org/projects/nirs_spm/, ...
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This thesis investigates how recurrent face-to-face social interactions engender relatively invariant patterns of being together that cause those who instantiate them to act in ways that support their reproduction. Existing accounts within both cognitive science and sociology offer important insights into the consideration of patterns of being together. However, given their explanatory strategies, they struggle to integrate both ‘social’ and ‘individual’ levels of explanation. Herein a compatibilist account is developed, intended as a ‘third way’ that obviates the limitations of existing accounts. This compatibilist account — by integrating insights from across disciplines and theoretical frameworks — develops a philosophical vocabulary with which to maintain explanatory consistency when articulating patterns of being together and moving between individual and social levels of explanation. It relies heavily on an extension of the enactive notion of autonomous habits to the social domain, redescribing patterns of being together as habituated participatory sense-making frames. Participatory sense-making frames result from processes of coenhabiting, i.e. processes of ongoing social habit making implicit in the dynamics of recurrent social interactions. Such processes are one primary means by which we produce and reproduce the relatively stable forms that characterise our shared worlds. These habituated frames embed much of the normativity of social life, and can serve our felicitous coordinations therein, allowing us to feel well situated, particularly in contexts within which we have some history of interacting. However, when they are not well aligned, they lead to tensions that result in either the production of novel frames or breakdowns in social interaction. The account developed has implications for many domains of human action, from psychotherapy to epistemology, and from critical studies to the development of political and ecological praxes.
... Regarding the social influence on synchronization performance, Dai et al. (2018) conducted a real-person jointtapping hyperscanning experiment and found interpersonal SMS performance was better in a bidirectional than in unidirectional condition, suggesting bidirectional condition can be considered as more cooperative than unidirectional condition. Interestingly, two-person studies showed the right PFC of two interactive individuals exhibited synchronization during joint-tapping tasks (Cheng et al., 2015;Baker et al., 2016;Pan et al., 2017). It is, therefore, possible that even a simple motor task if openly socially framed can affect the neural activation of the participants engaged in the synchronization task. ...
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This research explored the effect of explicit Interoceptive Attentiveness (IA) manipulation on hemodynamic brain correlates during a task involving interpersonal motor coordination framed with a social goal. Participants performed a task requiring interpersonal movement synchrony with and without a social framing in both explicit IA and control conditions. Functional Near-Infrared Spectroscopy (fNIRS) was used to record oxygenated (O2Hb) and deoxygenated hemoglobin (HHb) changes during the tasks. According to the results, the prefrontal cortex (PFC), which is involved in high-order social cognition and interpersonal relations processing, was more responsive when inducing the explicit focus (IA) on the breath during the socially framed motor task requiring synchronization, as indicated by increased O2Hb. In the absence of a broader social frame, this effect was not significant for the motor task. Overall, the present study suggests that when a joint task is performed and the individual focuses on his/her physiological body reactions, the brain hemodynamic correlates are “boosted” in neuroanatomical regions that support sustained attention, reorientation of attention, social responsiveness, and synchronization. Furthermore, the PFC responds significantly more as the person consciously focuses on physiological interoceptive correlates and performs a motor task requiring synchronization, particularly when the task is socially framed.
... Ample research evidence suggested the role of INS in the right TP in social interaction (Cheng, Li, & Hu, 2015;Pan, Cheng, Zhang, Li, & Hu, 2017). Stolk et al. found both the correlation and causal relationship between the right TP and the evolution of the communication system (Stolk et al., 2013(Stolk et al., , 2014. ...
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Conceptual alignment is a prerequisite for mutual understanding. However, little is known about the neurophysiological brain-to-brain underpinning during conceptual alignment for mutual understanding. Here, we recorded multi-channel electroencephalogram (EEG) simultaneously from two participants in Experiment 1 and adopted the dual-tACS techniques in Experiment 2 to investigate the underlying brain-to-brain EEG coupling during conceptual alignment and the possible enhancement effect. Our results showed that 1) higher phase-locking value (PLV), a sensitive measure for quantifying neural coupling strength between EEG signals, at the gamma frequency band (28-40 Hz), was observed in the left temporoparietal site (left TP) area between successful versus unsuccessful conceptual alignment. The left TP gamma coupling strength correlated with the accuracy of conceptual alignment and differentiated whether subjects belonged to the SUCCESS or FAILURE groups in our study. 2) In-phase gamma-band transcranial alternating current stimulation (tACS) over the left TP area increased the accuracy of subjects in the SUCCESS group but not the FAILURE group. 3) The effect of perspective-taking on the accuracy was mediated by the gamma coupling strength within the left TP area. Our results support the role of gamma-band coupling between brains for interpersonal conceptual alignment. We provide dynamic interpersonal neurophysiological insights into the formation of successful communication.
... At a neural level, correlations between brain regions from individuals engaged during social inference can be observed, which are significantly stronger during immediate social contact ( Bilek et al., 2015 ). In prior work, we demonstrated that these correlations can be found in the right temporo-parietal junction (rTPJ), a core region of the social brain network, implicated in the central coordination and control of social the bonding level between subjects is reflected in peak synchronization ( Kinreich et al., 2017 ;Pan et al., 2017 ), and mother-infant empathy and learning are associated with neural synchrony during their interactions ( Levy et al., 2017 ;Reindl et al., 2018 ). This kind of synchronization is thought to be a key aspect of therapeutic alliances (e.g., Koole and Tschacher, 2016 ;Kupper et al., 2016 ), and interestingly, within-group structure as well as between-group conflict relate to synchronization between members ( Jiang et al., 2015 ;Yang et al., 2020 ). ...
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Advances in social neuroscience have made neural signatures of social exchange measurable simultaneously across people. This has identified brain regions differentially active during social interaction between human dyads, but the underlying systems-level mechanisms are incompletely understood. This paper introduces dynamic causal modelling and Bayesian model comparison to assess the causal and directed connectivity between two brains in the context of hyperscanning (h-DCM). In this setting, correlated neuronal responses become the data features that have to be explained by models with and without between-brain (effective) connections. Connections between brains can be understood in the context of generalized synchrony, which explains how dynamical systems become synchronized when they are coupled to each another. Under generalized synchrony, each brain state can be predicted by the other brain or a mixture of both. Our results show that effective connectivity between brains is not a feature within dyads per se but emerges selectively during social exchange. We demonstrate a causal impact of the sender's brain activity on the receiver of information, which explains previous reports of two-brain synchrony. We discuss the implications of this work; in particular, how characterizing generalized synchrony enables the discovery of between-brain connections in any social contact, and the advantage of h-DCM in studying brain function on the subject level, dyadic level, and group level within a directed model of (between) brain function.
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Researchers from multiple fields have sought to understand how sex moderates human social behavior. While over 50 years of research has revealed differences in cooperation behavior of males and females, the underlying neural correlates of these sex differences have not been explained. A missing and fundamental element of this puzzle is an understanding of how the sex composition of an interacting dyad influences the brain and behavior during cooperation. Using fNIRS-based hyperscanning in 111 same- and mixed-sex dyads, we identified significant behavioral and neural sex-related differences in association with a computer-based cooperation task. Dyads containing at least one male demonstrated significantly higher behavioral performance than female/female dyads. Individual males and females showed significant activation in the right frontopolar and right inferior prefrontal cortices, although this activation was greater in females compared to males. Female/female dyad’s exhibited significant inter-brain coherence within the right temporal cortex, while significant coherence in male/male dyads occurred in the right inferior prefrontal cortex. Significant coherence was not observed in mixed-sex dyads. Finally, for same-sex dyads only, task-related inter-brain coherence was positively correlated with cooperation task performance. Our results highlight multiple important and previously undetected influences of sex on concurrent neural and behavioral signatures of cooperation.
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Functional near-infrared spectroscopy (fNIRS) is an increasingly popular technology for studying social cognition. In particular, fNIRS permits simultaneous measurement of hemodynamic activity in two or more individuals interacting in a naturalistic setting. Here, we used fNIRS hyperscanning to study social cognition and communication in human dyads engaged in cooperative and non-cooperative interaction while they played the game of Jenga™. Novel methods were developed to identify synchronized channels for each dyad and a structural node-based spatial registration approach was utilized for inter-dyad analyses. Strong inter-brain neural synchrony (INS) was observed in the posterior region of the right middle and superior frontal gyrus, in particular Brodmann area 8, during cooperative and obstructive interaction. This synchrony was not observed during the parallel game play condition and the dialogue section, suggesting that BA8 was involved in goal-oriented social interaction such as complex interactive movements and social decision-making. INS was also observed in the dorsomedial prefrontal region (dmPFC), in particular Brodmann 9, during cooperative interaction only. These additional findings suggest that BA9 may be particularly engaged when theory-of-mind is required for cooperative social interaction. The new methods described here have the potential to significantly extend fNIRS applications to social cognitive research.
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Romantic partners' emotions become coordinated in various ways and this may have implications for well-being (Butler (2011) Temporal interpersonal emotion systems: The TIES that form relationships. Personality and Social Psychology Review, 15, 367-393.). The present study uses a community sample of 44 committed heterosexual couples to examine whether cooperation, a generally beneficial relational process, is associated with emotional coordination and whether the pattern differs when men's emotions are coordinated with their female partners' prior emotions or vice versa. Using behavioral observations of cooperation and second-to-second measures of emotional experience during a face-to-face conversation, men showed the most positive emotional experience at high levels of mutual cooperation. As predicted, cooperation was associated with different coordination patterns for men and women, with high mutual cooperation predicting an inphase pattern for men (emotions changing in unison with their partners) and an antiphase pattern for women (emotions changing in opposite directions from their partners). Our results suggest that men and women may experience cooperation differently, despite engaging in similar behaviors.
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The neural mechanism of leader emergence is not well understood. This study investigated (i) whether interpersonal neural synchronization (INS) plays an important role in leader emergence, and (ii) whether INS and leader emergence are associated with the frequency or the quality of communications. Eleven three-member groups were asked to perform a leaderless group discussion (LGD) task, and their brain activities were recorded via functional near infrared spectroscopy (fNIRS)-based hyperscanning. Video recordings of the discussions were coded for leadership and communication. Results showed that the INS for the leader–follower (LF) pairs was higher than that for the follower–follower (FF) pairs in the left temporo-parietal junction (TPJ), an area important for social mentalizing. Although communication frequency was higher for the LF pairs than for the FF pairs, the frequency of leaderinitiated and follower-initiated communication did not differ significantly. Moreover, INS for the LF pairs was significantly higher during leader-initiated communication than during follower-initiated communications. In addition, INS for the LF pairs during leaderinitiated communication was significantly correlated with the leaders’ communication skills and competence, but not their communication frequency. Finally, leadership could be successfully predicted based on INS as well as communication frequency early during the LGD (before half a minute into the task). In sum, this study found that leader emergence was characterized by highlevel neural synchronization between the leader and followers and that the quality, rather than the frequency, of communications was associated with synchronization. These results suggest that leaders emerge because they are able to say the right things at the right time.
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This article evaluates a thesis containing three interconnected propositions. First, romantic love is a "commitment device" for motivating pair-bonding in humans. Second, pair-bonding facilitated the idiosyncratic life history of hominins, helping to provide the massive investment required to rear children. Third, managing long-term pair bonds (along with family relationships) facilitated the evolution of social intelligence and cooperative skills. We evaluate this thesis by integrating evidence from a broad range of scientific disciplines. First, consistent with the claim that romantic love is an evolved commitment device, our review suggests that it is universal; suppresses mate-search mechanisms; has specific behavioral, hormonal, and neuropsychological signatures; and is linked to better health and survival. Second, we consider challenges to this thesis posed by the existence of arranged marriage, polygyny, divorce, and infidelity. Third, we show how the intimate relationship mind seems to be built to regulate and monitor relationships. Fourth, we review comparative evidence concerning links among mating systems, reproductive biology, and brain size. Finally, we discuss evidence regarding the evolutionary timing of shifts to pair-bonding in hominins. We conclude there is interdisciplinary support for the claim that romantic love and pair-bonding, along with alloparenting, played critical roles in the evolution of Homo sapiens. © The Author(s) 2014.
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Romantic love is a motivational state associated with a desire to enter or maintain a close relationship with a specific other person. Studies with functional magnetic resonance imaging (fMRI) have found activation increases in brain regions involved in processing of reward, emotion, motivation when romantic lovers view photographs of their partners. However, not much is known on whether romantic love affects the brain’s functional architecture during rest. In the present study, resting state functional magnetic resonance imaging (rsfMRI) data was collected to compare the regional homogeneity (ReHo) and functional connectivity (FC) across a lover group (LG, N=34, currently intensely in love), ended-love group (ELG, N=34, romantic relationship ended recently), and single group (SG, N=32, never fallen in love).The results showed that:1) ReHo of the left dorsal anterior cingulate cortex (dACC) was significantly increased in the LG (in comparison to the ELG and the SG); 2) ReHo of the left dACC was positively correlated with length of time in love in the LG, and negatively correlated with the lovelorn duration since breakup in the ELG; 3) functional connectivity (FC) within the reward, motivation, and emotion network (dACC, insula, caudate, amygdala and nucleus accumbens) and the social cognition network (temporo-parietal junction (TPJ), posterior cingulate cortex (PCC), medial prefrontal cortex (MPFC), inferior parietal, precuneus and temporal lobe) was significantly increased in the LG (in comparison to the ELG and SG); 4) in most regions within both networks FC was positively correlated with the love duration in the LG but negatively correlated with the lovelorn duration in the ELG. This study provides first empirical evidence of love-related alterations of brain functional architecture. The results shed light on the underlying neural mechanisms of romantic love, and demonstrate the possibility of applying a resting state approach for investigating romantic love.
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In daily life, INTERPERSONAL: interactions are influenced by uncertainty about other people's intentions. Face-to-face interaction reduces such uncertainty by providing external visible cues such as facial expression or body gestures and facilitates shared intentionality to promote BELIEF OF COOPERATIVE DECISIONS AND ACTUAL COOPERATIVE BEHAVIORS IN INTERACTION: . However, so far little is known about INTERPERSONAL: brain synchronization BETWEEN TWO PEOPLE: engaged in naturally occurring face-to-face interactions. In this study, we combined an adapted ultimatum game with FUNCTIONAL: near-infrared spectroscopy (fNIRS) hyperscanning to investigate how face-to-face interaction impacts INTERPERSONAL: brain synchronization during economic exchange. Pairs of strangers interacted repeatedly either face-to-face or face-blocked, while THEIR ACTIVATION WAS SIMULTANEOUSLY MEASURED: in the right temporo-parietal junction (rTPJ) and the CONTROL REGION: , right dorsolateral prefrontal cortex (rDLPFC). Behaviorally, face-to-face interactions increased shared intentionality between strangers, LEADING MORE POSITIVE BELIEF OF COOPERATIVE DECISIONS AND MORE ACTUAL GAINS IN THE GAME: . FNIRS results indicated increased INTERPERSONAL BRAIN: synchronizations during face-to-face interactions in rTPJ (but not in rDLPFC) with greater shared intentionality between partners. These results HIGHLIGHTED THE IMPORTANCE OF RTPJ IN COLLABORATIVE SOCIAL INTERACTIONS: during face-to-face economic exchange and warrant future research that combines face-to-face interactions with fNIRS hyperscanning to study social brain disorders such as autism.
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Previous studies have shown that brain activity between partners is synchronized during cooperative exchange. Whether this neural synchronization depends on the gender of partner (i.e., opposite or same to the participant) is open to be explored. In current study, we used functional near-infrared spectroscopy (fNIRS) based hyperscanning to study cooperation in a two-person game (female-female, female-male, and male-male) while assaying brain-to-brain interactions. Cooperation was greater in male-male pairs than in female-female pairs, with intermediate cooperation levels for female-male pairs. More importantly, in dyads with partners with opposite gender (female-male pairs), we found significant task-related cross-brain coherence in frontal regions (i.e., frontopolar cortex, orbitofrontal cortex, and left dorsolateral prefrontal cortex) whereas the cooperation in same gender dyads (female-female pairs and male-male pairs) was not associated with such synchronization. Moreover, the changes of such interbrain coherence across task blocks were significantly correlated with change in degree of cooperation only in mixed-sex dyads. These findings suggested that different neural processes underlie cooperation between mixed-sex and same-sex dyadic interactions. Hum Brain Mapp, 2015. © 2015 Wiley Periodicals, Inc. © 2015 Wiley Periodicals, Inc.