Absence of a Lover Promote Dyadic Competition through the Strengthened Interpersonal Neural Synchronization in the Intimate Relationship

doi:10.21203/rs.3.rs-2874889/v1

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Absence of a Lover Promote Dyadic Competition through the Strengthened Interpersonal Neural Synchronization in the Intimate Relationship

https://doi.org/10.21203/rs.3.rs-2874889/v1

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Interbrain synchronization is considered the foundation of consciousness. When people jointly complete a social interaction, there is an inevitable overlap in their cognitive activities; brain synchronization is also considered a sign of individuals completing social interaction together. Based on Darwin's sexual selection theory, this study explored the influence of intimate relationship lover's companionship on female individual competitive interaction and peer brain coupling with competitors through EEG hyperscanning technology, using visual cue-target paradigm and taking inter-brain synchronized phase lock value (PLV) as a measurement index. The research results showed that in competitive interactions, there is a significant increase in theta and alpha frequency band activity between women and their competitors' brains. Brain synchronization is strongest when lovers are not around and women compete with same-sex competitors. In addition, there was a significant negative correlation between brain synchronization and behavioral DRT. The research results indicate that intimate companionship impacts the early alertness and late cognitive execution mechanisms of female individuals in competition. Women tend to focus on competitive tasks when their partner is not around. Moreover, due to intimate relationships, women in the romantic group pay less attention to opposite-sex competitors, while they pay more attention to same-sex competitors. This study demonstrates the impact of intimate relationship partner companionship status and opponent gender on individual female competition and improves the theoretical explanation of intimate relationships and competitive interaction.

EEG

hyperscanning

competition

intimacy

gender

With the rapid development of today's society, competition has become an essential topic of Social neuroscience. Competition stimulates the creative spirit and affects people's lives and the development of intimate relationships (Chuang et al., 2015). In Darwin's sexual selection theory, there is a discussion about competition. The first is what he calls the law of competition, which is competition between individuals of the same sex (usually male), and the second is the taste of beauty, which means that individuals of a specific personality (typically female) choose partners based on specific innate preferences (Darwin, 1981). It can be seen that there is also competition in the mate choice of individual intimate relationships. Women often choose the ideal spouse based on the results of male competition, and competition mainly occurs between individuals of the same sex. Deeply exploring competition can help establish intimate relationships.

Recent studies have shown that there is also competition between the opposite sex. With the development of social culture, competition between the opposite sex continues to increase, and the competitive scenarios that women need to face also continue to grow (Semenyna et al., 2020). A study showed that female archers exhibit higher levels of arousal and cognitive anxiety than male archers at different stages of the competition (Abdoshahi et al., 2023). When individuals face competition, female individuals are more sensitive to competition. In addition, women generally have higher awareness and influence on interpersonal communication processes (Acitelli, 1992). They tend to be more enthusiastic and submissive than men, while men tend to be more dominant and indifferent than women (Suh et al., 2004). There are significant differences between men and women in interpersonal communication. Competition is an interactive process, and no matter what kind of relationship group we are in, humans inevitably engage in social interaction with the outside world, and intimate relationships are no exception (Li et al., 2023). Previous studies have shown that people are more sensitive to interpersonal relationships in more intimate (such as romantic) relationships, and women generally exhibit higher interpersonal sensitivity (Jack et al., 2016). Therefore, female individuals may also be more influenced by intimate relationships when facing competitive interaction scenarios.

Previous theories suggest that an individual's efforts in competitive interactions can result in a certain degree of overlap between their behavior and more profound consciousness, manifested through synchronized brain activity (Gugnowska et al., 2022; Chang et al., 2023). The synchronized activity between individuals' brains can help us understand the cognitive neural mechanisms of women in competitive interactions and explore the impact of intimate relationships on the competition. There is evidence that when individuals receive positive feedback, compared with cooperation, their consciousness is more improved in competition, reflected in the inter-brain synchronization of the theta frequency band near the frontal lobe. With the improvement of subjective consciousness, the interbrain synchronization of individuals in competition is down (Balconi & Vanutelli, 2018). The relationship between individual brain synchronization and external performance feedback proves the connection between cognitive ability and theta frequency band and its role in individual brain synchronization. In addition, Putri et al. This indicates that the winner can monitor the opponent's activity in competitive interactions. The brain activity in the alpha frequency band is related to the individual's perception and consciousness. A near-infrared study found that acute psychosocial stress promoted competitive behavior among unfamiliar women and increased interpersonal neural synchrony (INS) in the dorsolateral prefrontal cortex of the right prefrontal cortex, revealing the dependent response patterns of women in social interaction to stress situations (Zhang et al., 2021). Based on the above research, we propose a hypothesis that under the influence of competition, differences in brain synchronization between female individuals will occur in the theta and alpha frequency bands, and the companionship status of intimate relationships and the gender of opponents may also have an impact on female individuals' competitive behavior.

Electroencephalography (EEG) is used to detect dynamic inter-brain oscillation activity with high temporal resolution (i.e., milliseconds), becoming one of the most commonly used techniques in hyper-scan research (Balconi & Vanutelli, 2018). This study uses EEG technology to explore the cognitive and neural effects of intimate relationship partner companionship status and opponent gender on inter-brain synchronization related to individual female competition through hyperscanning. Thus supplementing the field of female competitive psychology and brain activity and improving the theoretical explanation of intimate relationships and competition.

2.1 Participants

We used G∗Power (Faul et al., 2007) to determine the sample size needed. According to the analysis (f = 0.4, α = 0.4, 1-β = 0.8, analysis of variance: repeated measurement, inter-test factor), the required sample size was N = 52, a total of 104 people, that is, 13 pairs of subjects for each condition. A group of 120 healthy university students (30 male, 90 female, range: 18–25 years, mean: 20.30 years) participated in the study. To experiment, participants were randomly ordered into 60 dyads. A total of 60 pairs of participants (Dyad) were formed, including 15 partners competing with the same sex, 15 partners competing with the opposite sex, 15 partners not around competing with the same sex, and 15 partners not around competing with the opposite sex. Members of pairs were not acquainted with each other before the experiment. All participants were right-handed, with normal or corrected to normal vision/hearing, self-reported nonhistory of neurological/psychiatric disorders or drug abuse, and unaware of the experiment's purpose. The lover dyads reported being intensely in love (duration of “being in love”: M = 15.15 months, range = 2–36 months). Each participant signed informed consent before the experiment and was paid 10 to 20 yuan for participation. The study was approved by the Medical Ethical Committee of the local school by all provisions of the Declaration of Helsinki. All participants provided written informed consent.

2.2 Tasks and Procedures

The experiment consisted of a visual cue-target task (Cui et al., 2012; Cheng et al., 2015). Let the participants sit 50cm in front of the computer display. Among the lovers with uniform seats, the girl is on the left, the competitor is on the right, and the girl accompanies the lover on the left. In the condition that the lover is not accompanied, the position of the lover's companion is replaced by the stranger to eliminate the influence caused by mere gaze.

Figure 1 shows the sequence of events during the task. First, introduce the experimental requirements to the subjects, and present the corresponding instructions on the screen. Before the formal experiment, the exercise experiment was carried out, including five trials. The subjects were familiar with the competitive task process. Each trial began with the presentation of a 2 s blank, followed by the appearance of a gray ring in the center of the screen. This gray ring was the cue stimulus with a random duration between 0.6 and 1.5 s. After this random period, the target stimulus was presented. The target stimulus was a green circle with a gray border. Dyad members must press a button on their respective gamepad when viewing the target stimulus.

The target stimulus remained on the screen until both subjects responded. After the participants responded, a feedback screen was presented for 4 s. During the experiment, the subjects were required to press the keys as quickly as possible.

In the task, the original essential score of both sides was 100 points; 3 points added to the winner's total score, while 3 points reduced the loser. After both sides press the button, the feedback screen will display the winning and losing situation in the current competition task and their respective points, plus and minus, and cumulative points. Then enter the next test after a black-screen interval of 2000ms. The formal experiment includes three blocks; each block contains 20 tests, a total of 60.

2.3 Subjective Measurements

After the experiment, the female participants in the couples were asked to complete the Chinese version of the Interpersonal Reactivity Index-C (IRI), which included four subscales: perspective selection, personal pain, imagination, and empathy. A total of 22 questions were scored with Richter's five points (0–4, from "inappropriate" to "very appropriate")(Pang et al., 2022). In addition, we collected each participant’s attitudes towards her partner and the experiment; this information included: (1) the Competitor's ability; (2) The good-looking degree of the opponent. Participants used a 9-point Likert scale, which ranged from 1 (“not very much”) to 9 (“very much”) for all ratings. No discussion was allowed while rating.

2.4 Data Acquisition

Following the procedures described in Barraza et al. (2019) for the implementation of the EEG hyperscanning setup, The EEG signals were recorded using the 64-channel EEG recording system produced by Neuroscan, and the EEG signals of two subjects were recorded simultaneously using two 64-channel SynAmps 2, and then connected to an amplifier through a separate head box.

Signals from the two participants were synchronously recorded in a 64-channel workspace of the BrainVision Recorder software. The data were continuously acquired during the whole experiment. The electrodes were placed at the standard positions based on the comprehensive international 10–20 system. During the experiment, the average of the whole brain was used as the reference electrode. The vertical and horizontal electromyography (VEOG) were recorded by bipolar recording. The VEOG electrodes were placed in the middle of the left eye at 1 cm above the orbit, and 1 cm below the orbit, respectively, and the HEOG electrodes were placed in the left and right lateral canthus, respectively. Electrode impedances were kept below five kΩ. The EEG was filtered online from 0.05 to 100 Hz with a sampling rate of 1000 Hz. At the same time, E-prime 3.0 was used to record the subjects' reaction time (from the beginning of the stimulus to the subject's reaction time to the key press).

2.5 Data Analysis

2.5.1 Behavior performance

Response times (RTs) and winning trials were recorded for each participant dyad. To measure the closeness of subjects when completing tasks in the experiment, and to avoid abnormal values in the data, calculate the median of the absolute value of reaction time difference (median-DRT) of each pair of subjects in all trials. The smaller the value, the closer the subjects' reaction time is.

DRT = abs (RT1 − RT2)

To quantify the subjects' performance, we calculated the overall percentage of winning trials (PWT)(Cheng et al., 2015; Cui et al., 2012). First, the variables were checked for normality via Kolmogorov–Smirnov tests, and the median-DRT and PWT are by a normal distribution. This study uses univariate analysis of variance to analyze median-DRT with partner status and opponent sex as fixed variables, α The level is set to 0.05. At the same time, the PWT was also investigated by univariate ANOVA with partner status and opponent sex as fixed variables. Finally, Spearman bivariate correlation analysis was performed to test the relationship between brain synchronization and behavior.

2.5.2 EEG Data

EEG data were pre-processed using MATLAB R2018b with EEGLAB toolbox (Makeig & Delorme, 2004). The data preprocessing process includes reducing the sampling to 500Hz, manually removing the lousy segment, correcting the electromyographic artifact, performing 1 ~ 45 Hz bandpass filtering, and removing the amplitude of more than ± 100 µ V artifact test times. The EEG segmentation analysis time course is − 2000 ~ 1000 ms, with the stimulation time point as the zero point. EEG data were then re-referenced to the whole brain average. The inter-brain synchrony was estimated using the phase-locking value (PLV)(Lachaux et al., 1999). In short, this method difference calculates the brain phase difference between all electrode pairs in a time window and then evaluates the phase difference's stability through all experiments (Burgess, 2013). First, the segmented EEG signal is transformed by a short-time Fourier transform to obtain the time-frequency matrix of all segmented phase information. Then make a difference to the phase matrix of the two electrodes of each section, set φi and φj as the positive vector of the signal phase of the two electrodes i and j between the time window t and the frequency f. The phase difference between the two electrodes is:

φij = φi · φj × (φj × being the complex conjugate of φj )

For each time-frequency point, calculate the consistency of the phase differences of all segments at that time-frequency point, and obtain the PLV of each time-frequency point as follows:

PLVij = abs(1/N × ∑φij)

Where N is the number of tests, calculate the PLV of each pair of electrodes (i, j) between two subjects (electrode I belongs to subject one, and electrode j belongs to subject 2). The PLV ranges from 0 to 1, where 0 indicates that the two signals are unsynchronized, and 1 indicates perfect synchronization.

Select − 800 to − 200 ms before stimulation as the baseline correction baseline. Based on the previous literature and the spectrum generated in this study, select − 200–1000 as the time period of interest theta band (3 ~ 7 Hz) 、alpha band (8 ~ 12Hz) is defined as the frequency band of interest, and independent sample t-test, univariate analysis of variance and FDR correction are performed. The effect size was calculated with an r ratio (non-parametric) or Cohen’s d (parametric). Values of 0.2 indicated a small effect, 0.5 a medium effect, and 0.8 or greater a significant effect (Cohen, 1988). The α level was set at 0.05 for all tests. The same sensory stimuli and stimuli presentation sequence were used to avoid physical stimulus confounds or context differences between conditions. The only difference was the intention with which the participants performed the task.

3.1 Behavioral Performance

The two-way ANOVAs of variance were performed for median-DRT. We found that when the partner is not around, the total score of the scale (M = 72.57; SD = 8.89) is significantly higher than that of the scale when the partner is around (M = 64.00; SD = 11.36) (F(1, 56) = 10.53, p = 0.002, \({{\eta }}_{p}^{2}\) =0.158)—no statistical differences between gender and interaction.

Conduct univariate analysis of variance for PWT. The results showed that the main effect of gender was significant (F(1, 56) = 7.59, p = 0.008, \({{\eta }}_{p}^{2}\) = 0.12), the PWT of same-sex competition (M = 57.00; SD = 2.74) was significantly greater than that of heterosexual competition (M = 46.33; SD = 2.74), the main effect of partner status was not significant (F(1, 56) = 0.01, p = 0.909), and the interaction between partner status and gender was not significant (F(1, 56) = 0.12, p = 0.732). See Fig. 2.

3.2 Interbrain Phase Synchrony

The results of inter-brain synchronization showed that during competition, inter-brain synchronization between individuals appeared significantly in the alpha and theta frequency bands (Fig. 3).

3.2.1 Theta Interbrain Coupling

First, t-test analysis and FDR correction were performed for different groups. The results showed that when competing with the opposite sex, there was a significant difference in brain synchronization between FC5 and PO4 electrodes at 5-7hz of the theta frequency band of 500-700ms when the partner was not around or around (t(17.043) = -3.02, p = 0.008, Cohen's d = -1.10). When competing with the opposite sex, the inter-brain synchronization (M = 0.11; SD = 0.04) was more significant when the partner was not around (M = 0.08; SD = 0.01). During 700-1000ms, when the partner is not around, under the condition of competition with the same sex and the opposite sex, there is a significant difference in brain synchronization between the 5-7hz, F8, and FC5 electrodes in the theta frequency band (t(28) = 4.32, p < 0.001, Cohen's d = 1.58). That is, when the partner is not around, the brain synchronization of same-sex competition (M = 0.10; SD = 0.02) is significantly greater than that of heterosexual competition (M = 0.07; SD = 0.01).

The analysis of variance showed that the main effect of the companion state between FC5 and PO4 electrodes was significant (F(1, 28) = 9.53, p = 0.003, \({ {\eta }}_{\text{p}}^{2}\)= 0.15). When competing with the opposite sex, the inter-brain synchronization (M = 0.11; SD = 0.04) was more significant when the partner was not around (M = 0.08; SD = 0.01). The main effect of opponent gender between F8 and FC5 electrodes was significant (F(1, 28) = 10.19, p = 0.002, \({{\eta }}_{p}^{2}\) = 0.15). That is, when the partner is not around, the brain synchronization of same-sex competition (M = 0.10; SD = 0.02) is significantly greater than that of heterosexual competition (M = 0.07; SD = 0.01) (Fig. 4).

3.2.2 Alpha Interbrain Coupling

The results of t-test analysis and FDR correction showed that when competing with the same sex, the conditions of the partner's absence and presence were significantly different between C2 and P4 electrodes at 8-10hz of the 200-500ms alpha frequency band (t(28) = -4.16, p < 0.001, Cohen's d = -1.52). When competing with the same sex, the brain synchronization when the partner is not around (M = 0.13; SD = 0.03) is significantly greater than the brain synchronization when the partner is around (M = 0.09; SD = 0.02).

Univariate analysis of variance showed that the main effect of the companion state between C2 and P4 electrodes was significant (F(1, 28) = 13.91, p < 0.001, \({{\eta }}_{p}^{2}\)= 0.20). When competing with the same sex, the brain synchronization when the partner is not around (M = 0.13; SD = 0.03) is significantly greater than the condition when the partner is around (M = 0.09; SD = 0.02). Moreover, the interaction between C2 and P4 electrode points on the opponent's sex and partner status was significant (F(1, 28) = 5.57, p = 0.022, \({{\eta }}_{p}^{2}\)= 0.09). Further analysis shows that when the partner is not around, the brain synchronization of same-sex competition is significantly greater than that of heterosexual competition (M same-sex = 0.13, SD = 0.01; M heterosexual = 0.11, SD = 0.01; p = 0.012); When competing with the same sex, the inter-brain synchronization when the partner is not around is significantly greater than the inter-brain synchronization when the partner is around (M is not at = 0.13, SD = 0.01; M is at = 0.10, SD = 0.01; p < 0.001) (Fig. 4).

3.3 The PLV-Behavior Relation

To evaluate the degree of association between interbrain coupling and motor response, a Spearman bivariate correlation analysis was computed between the PLV values and the median-DRT of the dyads (Fig. 4). The correlation results showed that in the alpha frequency band of 200-500ms, under same-sex competition, the inter-brain synchronization of C2-P4 electrode points between the subjects was significantly negatively correlated with the median-DRT (r = -0.46*, p = 0.011). In the Theta frequency band of 5-7hz, 700-1000ms, when the partner is not around, the inter-brain synchronization of the F8-FC5 electrode between the subjects is significantly negatively correlated with the median-DRT (r = -0.41*, p = 0.026). In the Theta frequency band of 5-7hz, 500-700ms, under the condition that the subjects compete with the opposite sex, the inter-brain synchronization of FC5-PO4 electrode points is significantly negatively correlated with median-DRT (r = -0.46**, p = 0.010). The above results mean that the shorter the median DRT, the closer the task completion time, the more intense the competition, and the higher the inter-brain synchronization between subjects.

3.4 Subjective Measurements

Univariate analysis of variance was conducted with partner status and opponent sex as independent variables and the total score of the IRI scale as dependent variables. The results showed that when the partner was not around, the total score on the scale (M = 72.57; SD = 8.89) was significantly higher than that when the partner was around (M = 64.00; SD = 11.36) (F(1, 56) = 11.20, p = 0.\({\eta }_{p}^{2 }\)= 0.167). The main effect of opponent gender is not significant (F(1, 56) = 1.23, p = 0.273). The interaction between partner status and opponent sex is significant (F(1, 56) = 4.18, p = 0.046, \({ {\eta }}_{p}^{2}\) = 0.07). Further analysis showed that the total score of the IRI scale (M = 76.60; SD = 2.56) in competition with the same sex was significantly higher than that in competition with the opposite sex (M = 68.53; SD = 2.56) when the partner was not around, p = 0.030; When competing with the same sex, the total score of IRI scale (M = 76.60; SD = 2.56) was significantly higher when the partner was not around (M = 62.80, SD = 2.56), p < 0.001 (Fig. 5).

The results of Spearman correlation analysis showed that the evaluation of the ability performance (r = 0.433 **, p = 0.001) and the appearance value (r = 0.348 **, p = 0.006) of the female subjects in the couples were significantly positively correlated with the total score of the IRI scale, that is, the subjective impression of the participants on the opponents was positively correlated with the degree of empathy in the task (Fig. 6).

This study uses EEG hyper-scanning technology to analyze the behavior of binary entities participating in competitive interactions and the brain dynamics of oscillations and to explore the impact of intimate relationship partners' companionship status on individual competition. Our findings support the research hypothesis and demonstrate the particular neurodynamic viewpoint that the companionship status of personal relationships and the gender of competitors affect the brain synchronization of competitive social interactions among female individuals.

The results find that compared to the companionship state of a lover, female individuals have higher empathy scores, i.e., higher levels of empathy and shorter reaction times to complete competitive tasks when their partner is not around. Previous studies have shown that under competitive conditions, individuals reduce their inhibitory control mechanisms and improve their motor response-ability to defeat opponents, decreasing reaction time (Barraza et al., 2020). This is consistent with the results of this study. In addition, in this study, due to the absence of a partner's gaze, individuals may be more able to focus on competitive tasks without distraction while also paying more attention to their competitors and developing a certain level of empathy (Cazzato et al., 2015; Mehmood et al., 2021).

4.1 Late cognitive control affects Theta frequency band brain synchronization.

The study found that in the late stage of stimulus presentation, in heterosexual competition conditions, when the partner is not around, the theta frequency band brain synchronization between female individuals and their competitors near the inferior parietal lobule (IPL) is significantly greater than the partner's present condition. In the absence of a partner, the theta frequency band brain synchronization near the inferior frontal gyrus (IFG) of women competing with the same sex was significantly greater than that of women competing with the opposite sex. In previous studies, the Theta frequency band has been considered a marker of cognitive load, closely related to advanced cognitive functions such as cognitive control, memory encoding, and recall (Klimersch, 1999; Jensen & Tesche, 2002). Activation of brain activity in the Theta frequency band reflects an increased demand for specific cognitive functions such as situational memory recall and cognitive control (Babiloni et al., 2009; Sauseng et al., 2010). IPL is closely related to cognitive functions, such as viewpoint-taking (Iacoboni & Dapretto, 2006) and self-other differentiation (Jackson & Decety, 2004; Abu Akel & Shamay Tsoory, 2011). Compared to cooperation, competitive situations require additional cognitive resources, and IPL exhibits more pronounced brain-to-brain synchronization in competition compared to the association (Liu et al., 2017). In this study, while the partner is around, female individuals may also want to maintain a good image in front of their partner while completing competitive tasks, which suppresses competitive behavior and fails to make in-depth evaluations and adjustments to their competitive outcomes promptly in the late stages of the competition (Cazzato et al., 2015; Mehmood et al., 2021). When a partner is not around, female individuals may be more able to immerse themselves in competitive interactions like their competitors, actively recalling competition and related experiences in the late stages of competitive stimulation and trying to control the competitive situation (Arnott & Elwood, 2008). Thus, when the partner is not around, the level of brain synchronization between female individuals and their competitors is significantly higher.

From the perspective of women themselves, compared to single individuals, when female individuals are in a stable relationship, their attention to opposite-sex partners decreases (Karremans & Verwijmergen, 2008). Some studies have shown that the theta band is related to the performance of working memory that transmits stimulus-specific information to the visual cortex under focused attention (Ekstrom et al., 2005). Consistent with the above, in this study, the theta frequency band of brain synchronization was higher during same-sex competition. This may result from women's greater attention and more focused attention toward same-sex competitors than strangers of the opposite sex. This enables female individuals to acquire working memory, adjust and plan their behavior in time, and win the competition in the late stage after completing competitive key actions, along with competitors' performance.

4.2 Alpha band brain synchronization as a marker of alertness

Based on previous studies, it has been found that the alpha frequency band is closely related to the allocation of attention in selective tasks and the overall alertness of the brain. When an individual's alertness decreases, the alpha frequency band activation increases (Dikker et al., 2020). Song et al. (2022) found that curling athletes exhibit higher brain activity during competitive tasks in the alpha frequency range than inexperienced individuals. This result indicates that the brain activity in the alpha frequency band is related to factors such as the individual's competitive experience, alertness when receiving task stimuli, and visual processing level towards stimuli.

In this study, in the early stage of stimulus presentation, when female individuals competed with same-sex individuals without their partners, the alpha frequency band near the IPL had the highest degree of brain synchronization. This may be because, at this stage, empathy cognition has not yet been deeply processed, and the alpha frequency band only reflects the results of individual visual processing when viewing the same stimulus (Clements et al., 2023). As women, both sides of the competition can guess each other's intentions from a familiar perspective of their gender and predict their competitors' subsequent actions, thus reducing the alertness of individual women and their opponents (Ravreby et al., 2022). Based on the above, it can be seen that whether a lover is with them may affect the alertness of female individuals when participating in the competition. In the early stages of competitive tasks, compared to the presence of a certain level of competitive pressure when the partner is around, when the partner is not around, the pressure on female individuals during early stages of competitive tasks may be lower (Órfão et al., 2023).

The results of this study on the correlation between brain synchronization and behavioral DRT showed a significant negative correlation between subjects' DRT and brain synchronization PLV, indicating that the shorter the difference in reaction time between subjects, the stronger the brain synchronization between subjects. This trend is correlated in the late stage of theta band stimulation and the early stage of the alpha band stimulation program. This result also confirms the possible impact of focus (Ekstrom et al., 2005). When both individuals are focused on competing tasks, when the target appears, the individual will immediately press the button to react. Compared to distract individuals who are not focused on the job, individuals with high concentration have closer reaction times and higher levels of brain synchronization (Boxhoorn et al., 2022; Bowen et al., 2023).

In addition, based on subjective results, it can be concluded that when a partner is not around, the overall IRI score of an individual is higher, and women are more likely to empathize with same-sex individuals. Therefore, in same-sex competition, they may better understand each other's intentions than when competing with the unfamiliar opposite sex, which has been confirmed in previous studies (Pang et al., 2023). Individuals pay more attention to and empathize with same-sex competitors, increasing brain synchronization when competing with same-sex individuals (Kang et al., 2022). Moreover, from the subjective measurement results, it can be seen that there is a significant positive correlation between the personal impression and empathy of participants towards their competitors. When facing the attractive and capable opposite sex, participants may have more compassion toward their competitors and are more willing to invest more energy when competing with them (Balconi et al., 2022).

However, there are also some limitations in this study. Firstly, due to venue limitations, the lovers studied in this study are concentrated on university campuses, and the lovers are also students. The research results can only illustrate university campuses' social interaction and competition situation. As for the groups of working couples, married couples, elderly partners, etc., this result does not yet represent their research results. Future research can vertically expand the subject population to explore the impact of intimate relationships on competition in different age groups and scenarios. Secondly, this study did not control for the potential impact of female physiological cycles on competition in romantic relationships. Previous studies have shown that women's response to social stress may be influenced by the menstrual cycle (Albert et al., 2015; Banis & Lorist, 2017; Duchesne & Pruessner, 2013; Kirschbaum et al., 1999). In the process of competitive interaction, there will inevitably be some competitive pressure, and female physiological cycles may also have a particular impact on competitive interaction. Future research can consider studying the comprehensive effect of competition in intimate relationships and menstrual cycle stages on women's social interactions. Thirdly, this study only evaluated the length of time intimate relationship lovers had been in love and did not rate their level of intimacy or relationship patterns (Rice et al., 2022). Therefore, the impact of their partner's companionship on the level of brain synchronization between women and others may be inconsistent. Future research on intimate relationships should be conducted through questionnaires or interviews to gain a deeper understanding of the emotional status of participants and control such variables' impact on research results.

To sum up, based on the theory of sexual selection, this study studied the competitive social interaction neurodynamics of intimate relationship lovers through EEG hyperscanning technology. It proved that the companion status of lovers and the gender of competitors regulate competition. The companionship of a partner during competition can impact a woman's alertness in the early stages of the competition and profound cognitive control in the later stages. In contrast, women are more likely to concentrate on competitive tasks without a partner around them. In addition, when the partner is not around, women and women have higher brain synchronization, which indicates that when women have a stable intimate relationship, they pay less attention to the opposite sex. Compared with strange men, women and women have stronger empathy, greater attention, lower alertness, and higher brain synchronization. The application of ultra-scanning technology in competition can provide a more realistic understanding of real-time interpersonal interaction brain activity in real life, promote EEG understanding of social interactions related to intimate relationships, and provide insights for the evolution of intimate relationships that keep up with the times.

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No competing interests reported.

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Absence of a Lover Promote Dyadic Competition through the Strengthened Interpersonal Neural Synchronization in the Intimate Relationship

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Abstract

Figures

1. Introduction

2. METHOD

2.1 Participants

2.2 Tasks and Procedures

2.3 Subjective Measurements

2.4 Data Acquisition

2.5 Data Analysis

2.5.1 Behavior performance

2.5.2 EEG Data

3. RESULTS

3.1 Behavioral Performance

3.2 Interbrain Phase Synchrony

3.2.1 Theta Interbrain Coupling

3.2.2 Alpha Interbrain Coupling

3.3 The PLV-Behavior Relation

3.4 Subjective Measurements

4. Discussion

4.1 Late cognitive control affects Theta frequency band brain synchronization.

4.2 Alpha band brain synchronization as a marker of alertness

5. Conclusion

References

Additional Declarations

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