The self and our perception of its synchrony – Beyond internal and external cognition

The self is the core of our mental life which connects one ’ s inner mental life with the external perception. Since synchrony is a key feature of the biological world and its various species, what role does it play for humans? We conducted a large-scale psychological study (n = 1072) combining newly developed visual analogue scales (VAS) for the perception of synchrony and internal and external cognition complemented by several psychological questionnaires. Overall, our findings showed close connection of the perception of synchrony of the self with both internal (i.e., body and cognition) and external (i.e., others, environment/nature) synchrony being associated positively with adaptive and negatively with maladaptive traits of self. Moreover, we have demonstrated how external (i.e., life events like the COVID-19 pandemic) variables modulate the perception of the self ’ s internal-external synchrony. These findings suggest how synchrony with self plays a central role during times of uncertainty.


Introduction
When we experience ourselves within the flow of our thoughts or dancing in tune with our body, at the same rhythm with our partner and the music around us we experience as synchronous and connected with ourselves and the environment.This is synchrony as defined as the state of operating in accordance with the same time scale as something/someone else.Synchrony is a key feature of the biological world where different individuals of the same species often synchronize with each other, as for instance in the flight formation of birds (Gunnarsson et al., 2004).Given its biological preponderance including its manifestation in the human brain (Raut et al., 2021), one would assume that synchrony is also present on the psychological level, especially in the human mind in its perception of the self.The self is a key feature of our mental life, which is involved in both internal cognition of one/s inner mental life and external perception of the outer environment.On the one hand, our self allows for internal cognition like mind-wandering (Christoff et al., 2016;Scalabrini, Schimmenti, et al., 2022;Smallwood et al., 2021) and episodic simulation (e.g., mental time travel) (Northoff, 2017;Schacter et al., 2012).At the same time, the self is also related to the perception of the external environment, including its social relationship to others (Atzil et al., 2014;Cirelli, 2018), connectedness (Carhart-Harris et al., 2018), empathy (Koehne et al., 2016;Levy & Feldman, 2019;Yu et al., 2018), and, more generally, nature (Gunnarsson et al., 2004;Motter, 2010;Ravignani, 2017).Given its role in both internal cognition and external perception, the self has been characterized as an integrative function (Sui & Humphreys, 2015) that provides an internal-external relation and thereby serves as "psychological baseline" (Northoff, 2016;Scalabrini, Mucci, et al., 2022;Scalabrini, Schimmenti, et al., 2022;Scalabrini et al., 2021).Is synchrony a key feature in our perception of the self's internal-external relation?Is the perception of the self as an internal-external relation related to its adaptive and maladaptive features as for instance during externally threatening events?Addressing these yet open questions is the goal of our study.
There are various lines of indirect evidence for a key role of synchrony with respect to our self.In the human context, synchronization with the own self and others promotes cooperation and compassion (Valdesolo & DeSteno, 2011;Wiltermuth & Heath, 2009).Intriguingly, the experience of synchrony with the own self and others can dramatically increase during meditation practice (Cooper et al., 2022).Experience of synchrony finds its priors in early internal-external relational experiences with primary caregivers in the context of attachment.Indeed, bio-behavioral synchrony is an important aspect of mother-infant attachment (Feldman, 2007), that contribute to the formation of the sense of self and relatedness (Mucci & Scalabrini, 2021;Scalabrini et al., 2018;Scalabrini, Mucci, et al., 2022).Through synchronization the mother regulates the infant's temperature (Levin, 2006), heart rate (Feldman et al., 2011), sleep and arousal (Feldman et al., 2002).Mothers regulate their infants' immune function by breastfeeding, synchronizing their gut microbiota and antigen-specific antibodies (Arrieta et al., 2014).
All these findings converge with the theory about the origin of human intersubjectivity developed by Colwyn Trevarthen.He gave synchrony a key role in emotional nonverbal communication between caregiver and infant with the function of regulating states of both members of the dyad (Trevarthen, 1993).More specifically, he described the experience of synchrony as the spatiotemporal coordination between the parent's and the child's nonverbal behavior and communicative signals during social interactions in ways that enhance positive reciprocity and mutual engagement (Stern, 1985;Trevarthen & Aitken, 2001).Intriguingly, more recent research found that visuo-tactile synchrony vs. asynchrony can be discriminated by newborns (Filippetti et al., 2013).This process of detecting "amodal properties" such as synchrony between different senses has been recently defined as "mentalization of the body" (Ciaunica & Fotopoulou, 2017;Fotopoulou & Tsakiris, 2017), indicating the capacity of the individual of organizing sensory input of both subjective and intersubjective origins in a unitary multi-modal schemata that include both internal-interoceptive and externalexteroceptive stimuli.
In this context, we can argue that the mother-infant relationship is a prior for developing the sense of synchrony and connectedness of the self and its relationship with the environment, which can be considered as the capacity to integrate internal and external stimuli.Furthermore, the experience of synchrony as well as the experience of connectedness, otherwise called "relational alignment" (Scalabrini et al., 2018;Scalabrini, Mucci, et al., 2022) is the prerequisite that shapes the baseline for the sense of subjectivity and intersubjectivity that, in turn, depend on the degree of attunement and synchronization to the infant's needs by the parents (Atzil & Barrett, 2017;Mucci, 2021;Mucci & Scalabrini, 2021;Schore, 2011).These first synchronic experiences shape the physiological and psychological "baseline" activity (Northoff, 2016;Northoff & Scalabrini, 2021b;Northoff et al., 2022;Scalabrini, Schimmenti, et al., 2022;Scalabrini et al., 2021).The quality and the organization of this psycho-physiological baseline needs to be considered as dependent on the relational experiences, firstly with the attachment figure (e.g., the mother/caregiver) and, secondly, with an extended social world which can impact the self both in a positive or adverse/traumatic way (Ciaunica, Constant, et al., 2021;Di Plinio et al., 2022;Mucci & Scalabrini, 2021;Scalabrini, Mucci, et al., 2022).When lack of attunement and synchrony characterize early relational life experience disorganized attachment, dissociative predisposition, feelings of disconnections and self-dysregulation (Ciaunica, Charlton, et al., 2021;Ciaunica, Roepstorff, et al., 2021;Farina et al., 2019;Liotti, 1992Liotti, , 2006;;Mucci, 2021;Scalabrini et al., 2020;Schimmenti & Caretti, 2016;Schore, 2013) becomes rooted in the self and its "psychological baseline".These experiences shape the characteristics of the self in terms of resiliency on one hand or vulnerability on the other.Altogether, these observations about the early mother-infant relation strongly speaks for a key role of synchrony in constituting the self as an internal-external relation in later adulthood.
A multitude of studies investigate the objective neural and psychological-behavioral effects of self-referential vs non-self-referential stimuli (Frewen et al., 2020;Qin et al., 2020).In contrast, the subjective perception or experience of the self, including its role in both internal cognition and external perception, remain to be investigated.Filling in this gap in our knowledge, we conducted a large-scale psychological study (n = 1072) where we combine standardized-psychological questionnaires targeting the self in its various domains (e.g., interoceptive awareness, self-concept clarity and connectedness with the natural environment) with newly developed subjective rating scales (visual analogue scales/VAS) on the perception of synchrony with self and its internal-external relation.
We hypothesize a key role (and its centrality using network analysis) of the perception of synchrony with both internal mentalbodily and external social-ecological features.We also expect that the perception of synchrony is positively related with the different psychological questionnaires of different facets of the self, while negatively correlated with maladaptive manifestations (e.g., rumination, emotional dysregulation, fear of covid and general psychopathological symptoms).Finally, we hypothesize the malleability in the perception of our self's internal-external synchrony external features like the COVID pandemic (showing a difference in the perception of synchrony before vs. after COVID).

Participants
The collection of data started around June 2020 during the first wave of the COVID-19 pandemic and one thousand and seventytwo individuals participated to the study and signed the electronic informed consent.They completed information on sociodemographic variables, the visual analogue scale (VAS) questions section of the survey and a set of psychological self-reports.Overall, the study involved a total of 1072 adults from different nationalities (311 males, 29 %; 761 females, 71 %).More information about participants can be found in Supplementary Information.

Procedures
All participants were recruited trough an online survey via social networks (e.g., Facebook and web-forums) and provided informed consent prior to participation in the study.This study was consistent with the ethical principles of the American Psychological Association (APA).Privacy of participants was guaranteed in accordance with the European Union General Data Protection Regulation 2016/679.The study is part of the project SYNC (no.20023).

Experience/Perception of self and internal-external cognition -visual analogue scale (VAS) assessment
In order to investigate perception or experience, a set of visual analogues scales (VAS) were created ad hoc for this investigation.These VAS questions were created to probe different features of the personal experience or perception related to (i) synchrony with self, bodily, social, and environmental features; (ii) internal-external perception of constraints, like the degree of traumatic perception, and (iii) internal cognition like thoughts about the self and mental time travel (Table 1).These questions represent the initial conceptual framework theorized by the authors of a "psychological baseline" featured by the experience of synchrony of the self as different by the mental cognitive level of internal-external representations (Northoff & Huang, 2017;Northoff & Scalabrini, 2021a;Scalabrini, Mucci, et al., 2022;Scalabrini, Schimmenti, et al., 2022).These VAS were applied twice to probe the subjective experience of the individuals related to "during pandemic" (VAS-A) and secondly related to "before the pandemic" (VAS-B) (See Table 1 for questions of VAS "during Covid-19"; See Table S1 for questions of VAS "before Covid-19").

Psychological questionnaires
In addition to VAS, we also included a set of psychological questionnaires for the assessment of adaptive and maladaptive features related to the self: Self-Concept Clarity -SCC (Campbell et al., 1996).The SCC is a 12-item measure designed to assess the extent to which a person's self-beliefs are clearly and confidently defined, internally consistent, and stable.Items are rated on a 5-point Likert-type scale ranging from "Strongly disagree" to "Strongly agree."Examples of items include "my beliefs about myself often conflict with one another," "sometimes I feel that I am not really the person that I appear to be".In our sample the SCC scale has shown high internal consistency (Cronbach's α = 0.85).
Multidimensional Assessment of Interoceptive Awareness -MAIA (Mehling et al., 2012).The MAIA is a 32-item instrument that assesses interoceptive and body awareness on 6-point Likert-type scales that range from 0 (Never) to 5 (Always).It comprises eight scales, namely Noticing, Not-Distracting, Not-Worrying, Attention Regulation, Emotional Awareness, Self-Regulation, Body Listening, and Trusting.For the aim of the study, we administered only the scales that we thought might be more relevant for our investigation, i. e., Self-Regulation (Cronbach's α = 0.83) -ability to regulate psychological distress by attention to body sensations; Body Listening (Cronbach's α = 0.87) -active listening to the body for insight; Trusting (Cronbach's α = 0.89) -experiences of one's body as safe and trustworthy.
Difficulties in Emotion Regulation Scale -DERS (Gratz & Roemer, 2004).The DERS is a 36-item self-report questionnaire with items rated on a 5-point Likert scale.The DERS consists of six subscales-nonacceptance (e.g."when I'm upset, I feel ashamed at myself for feeling that way"), goals (e.g."when I'm upset, I have difficulty focusing on other things"), impulse (e.g."when I'm upset, I lose control over my behaviors"), awareness (e.g."I pay attention to how I feel"), strategies (e.g."when I'm upset, I believe that wallowing in it is all I can do"), and clarity (e.g."I have no idea how I am feeling").The higher the total score is, the higher the level of emotional dysregulation.For the purposes of this study, we considered only the DERS total score that in our sample has shown high internal consistency (Cronbach's α = 0.94).
Connectedness to nature -CNS (Mayer & Frantz, 2004).The CNS comprises 14 questions, such as "I often feel a sense of oneness with the natural world around me" and "I recognize and appreciate the intelligence of other living organisms," which assess the sense of oneness with the natural world.These questions are rated using a 5-point response scale, ranging from 1 (strongly disagree) to 5 (strongly agree).An overall score is calculated based on the mean of the responses to all questions, with higher scores reflecting greater connectedness to nature.This scale is widely used to measure the strength of respondents' traits that promote feelings of being emotionally connected to the natural world (Frantz et al., 2005;Howell et al., 2011;Kamitsis & Francis, 2013;Mayer et al., 2009).In our sample the CNS scale has shown high internal consistency (Cronbach's α = 0.85).
Identification with All Humanity -IWAH (McFarland et al., 2012).The IWAH consists of nine, 5-point Likert-type items covering different aspects of identification (e.g., "we" thinking, helping others, loyalty).For each of these aspects, participants indicated the extent to which this aspect described their relationship to people in their own community, to people from their own nation, and to people from all around the world (e.g., How much do you identify with [that is, feel a part of, feel love toward, have concern for] each of the following?(a) People in my community; (b) People of my nationality, (c) All humans everywhere).As a measure of identification with humanity we focused only on the items concerning "all humans everywhere".In our sample the scale showed high internal consistency (α = 0.88).
Rumination-Reflection Questionnaire -RRQ (Trapnell & Campbell, 1999).The RRQ is a 24-item measure that investigates rumination (RUM) and reflection (REF).Reflection and rumination are considered divergent functional modes or structures of thoughts related to the self: for instance, reflection is related to the item "My attitudes and feelings about things fascinate me", while rumination is featured by items like "My attention is often focused on aspects of myself I wish I'd stop thinking about".The items are divided equally between the two subscales, evaluated on a five-point Likert scale, from 1 ("completely disagree") to 5 ("completely agree").In our sample Cronbach's alpha for RUM was 0.87, Cronbach's alpha for REF was 0.86.
Multidimensional Assessment of COVID-19-Related Fears -MAC-RF (Schimmenti et al., 2020).The MAC-RF is an eight-item self-report measure scored on a five-point Likert scale (from 0 to 4) that was developed by the authors of this article to assess the eight facets of fear identified by Schimmenti and colleagues.Scores of the MAC-RF can range from 0 to 32, with higher scores indicating higher COVID-19-related fears.In our study MAC-RF showed good internal consistency (Cronbach's α = 0.73).
The DSM-5 Self-Rated Level 1 Cross-Cutting Symptom Measure (Association, 2013), was used to assess psychopathological symptoms.This measure includes 23 items rated on a 4-point Likert-type scale ranging from "very false or often false" to "very true or often true".Each item investigates how often an individual has suffered from specific symptoms in the last 2 weeks.For the purposes of this study, we considered only the total score that in our sample has shown high internal consistency (Cronbach's α = 0.89).

Statistical analysis
Jamovi and JASP were used to analyze the data.Cronbach's α coefficient was used to assess the internal consistency of the psychological questionnaires.Data were initially examined through simple descriptive statistics, while between-group differences were tested by means of independent sample t-test and Chi-square test.
The logic of the subsequent statistical analyses comprised different steps: 1) Principal component analysis.To reduce the dimensionality of the data we extracted underlying latent components of the VAS items trough a principal component analysis (PCA).The use of the PCA allows the extraction of relevant latent variables.Keiser-Meyer Olkin criteria (KMO > 0.6) and Bartlett's Test of sphericity (<0.05) were explored.After the administration of the PCA we firstly gave names to the factors, and secondly, we extracted their respective factorial values.

2) Correlation between VAS components and psychological questionnaires
Pearson's r coefficient was used to evaluate the association between the factors of the PCA and the psychological questionnaires.Bonferroni correction for multiple comparisons was performed on the obtained correlation coefficients, such that only p values (before correction) were considered significant below p < 0.05/number of calculated correlations.
A. Scalabrini et al. 3) Graph-theoretical measure (EBICglasso) First network analysis was applied to the VAS items that constituted the first component of the PCA (intra-network analysis approach), secondly network analysis was applied to a larger network comprising all variables included in the PCA (inter-network analysis approach).These analyses were administered in order to establish how the different VAS items are related to each other's and which of the single VAS items act as a central node in the intra-and inter-network.
Network analysis allows calculating closeness (the inverse of the sum of all shortest paths from the node of interest to all other nodes), betweenness (the number of shortest paths that pass through the node of interest), and degree of centrality (the sum of the absolute input weights of that node.In general, a higher centrality measure indicates that this node is more central to the network) using EBICglasso technique, i.e. computing a sparse gaussian graphical model with the graphical lasso (Friedman et al., 2008).Tuning parameter is set at 0.5 using the Extended Bayesian Information criterium (EBIC); this 0.5 indicates that more parsimonious models with fewer edges are preferred.This method provides a network of partial correlation coefficients with a limited number of spurious edges (Epskamp et al., 2018;Epskamp et al., 2012).Centrality indices are plotted using standardized z-scores to facilitate interpretation.
4) Difference in the perception of synchrony during the pandemic vs. before the pandemic As a last step, a) by means of paired sample t-test we tested the differences between VAS related to before and after pandemic.Finally, as a further control, G*Power 3.1 (Faul et al., 2009) was used to conduct post-hoc power analysis on the total sample of 1072 subjects for an expected correlation (r = 0.20; α = 0.05).The analysis revealed a Power (1 -β err prob) of 0.99 suggesting an optimal sample size.

Descriptive statistic
Table S2 (supplementary material) shows descriptive statistics for VAS and Table S3 (supplementary material) shows descriptive statistic for the psychological questionnaire.Table S2bis and S3bis (in supplementary material) also show gender differences for VAS and psychological questionnaires respectively.

Perception of self and cognition -VAS and principal component analysis
In order to reduce the dimensionality of the VAS data and increase their interpretability, we conducted a principal component analysis (PCA).Kaiser-Meyer-Olkin measure of sampling adequacy (KMO) and Bartlett's Test of sphericity showed the suitability of data for the PCA (KMO = 0.73 l6; Bartlett's Test = p < 0.001).Results of Kaiser-Meyer-Olkin test suggested the presence of an adequate sample size relative to the number of items in the scale (Mulaik, 2009).Bartlett's Test evidenced that the correlation matrix was not an identity matrix, or a matrix whose diagonal entries are all 1, and all off diagonal elements are 0 (Mulaik, 2009).The PCA yielded three main components which together explained 51.4 % of the cumulative variance.
Specifically, the first component explained 20.8 % of the variance and included all items related to synchrony like with self, body, other and environment.We named the first component "Synchrony".Notably, none of the synchrony items was included in the other two factors (Table 2).Instead, the other two PCA components concerned perception of external constraints and internal cognition.VAS items for the second components explained 17.3 % of variance and included items focusing on perception of trauma, encloseness, freedom, and past thoughts.We named the second component as "Perception of Constraints".Finally, the third component explained 13.3 % of the variance and included VAS items like thought about present, future and thought about the self (see Table 3).We named the third component "Internal Cognition".Together, our findings clearly support the importance of our perception of synchrony with self, body, others and environment/nature as key component that is distinct from internal cognition and perception of external

constraints.
Since, the correlation between the three components resulting from the oblimin rotation was very low (r < 0.2; Synchrony -Perception of Constraints r = -0.155;Synchrony -Internal Cognition p = 0.126; Perception of Constraints -Internal Cognition p = 0.146) we reported data using the varimax rotation for the PCA.* p-value still significant after Bonferroni correction for multiple comparisons.
To further confirm the component structure of our VAS items we also performed PCA on VAS related to before covid (VASB) and we also controlled for gender differences.Intriguingly PCA analysis on VASB scales showed a highly similar structure (See Supplementary material, Table S4).To further confirm our results Table S6 and S7 in supplementary material show a highly similar structure for males and females in relation to VASA (Fig. 1).

Validation of VAS synchrony component -psychological rating scales relate to VAS
In a next step we extracted the factorial scores of each component, which we correlated with several psychological questionnaires.Intriguingly, this yielded major relationship of the scales with specifically the first PCA component, i.e., Synchrony, whereas there were only sparse correlations with the second component "Perception of constraints" (Table 3).
We observed significant positive correlations of the first PCA component, that is Synchrony, with various MAIA subscales (selfregulation, body-listening and trusting), with Self-concept clarity, with Connectedness with Nature scale, and with Identification with humanity (See Table 3 Correlations).These correlations suggest that higher degrees of synchrony in the VAS relate to higher degrees of interoceptive awareness, clarity of self, and connectedness with both nature and humanity/world.These data suggest that the perception of synchrony relates the self to both internal (body, cognition) and external (nature, humanity, environment) adaptive featuresone can thus speak of internal-external synchrony of self.In contrast, we obtained negative correlations of the Synchrony component, with the scales for emotion dysregulation, rumination, fear of covid and symptoms: the weaker the synchrony, the higher the dysregulation of emotions, the higher levels of rumination, and the more general symptomatology and covid-related fear.These data suggest that high synchrony of self provides some kind of prevention against subclinical cognitive-emotional and behavioral malfunction.(See Table 3Correlations).
Unlike the first PCA component, the second PCA component of the VAS, Perception of Constraints showed positive correlations with more or less those variables with which the first component, Synchrony, correlated negatively.Specifically, higher degrees in Perception of Constraints were positively related to higher degrees in symptoms, rumination, more dysregulation of emotions and COVID-related fear.Moreover, we observed a weaker but still significantly negative correlation of Perception of Constraints with Selfconcept clarity.Together, these data suggest that high levels of Perception of Constraints can be considered a risk factor for subclinical malfunction.Similar results were also found between components resulting from PCA on VAS before covid-19 and psychological questionnaires (Table S8 in supplementary material).
Last, intriguingly we did not observe any correlation between the third component "Internal Cognition" with other psychological scales.

Network structure of synchrony -Graph-theoretic analysis
The first PCA component included synchrony with Self, body, others and environment.What is the network relation among these different synchrony items?For that purpose, we applied a graph-theoretical measure that allows calculating the relationship among the distinct VAS items included in the first PCA factor, the synchrony of self (See Fig. 2).
The network analysis yielded high degrees of centrality, betweenness and closeness for specifically synchrony with self and synchrony Fig. 2. Network analysis of the first PCA -Synchrony -VASA items (Intra-network).
A. Scalabrini et al. with body whereas the other synchrony items showed lower values in these measures (Fig. 2).This suggests a key role of the internal synchrony of the self (e.g., mental self) (Qin et al., 2020) and its own body (synchrony with body) in constituting synchrony with external environment and the others.
Extending beyond the first PCA component (i.e., Synchrony), we next included all VAS items of all three PCA components in our network analysis.This again yielded high centrality for two synchrony items, namely synchrony self and synchrony with the body showing higher degree of centrality and betweenness (Fig. 3).Intriguingly, also the VAS thought of the self, belonging to the more cognitive component showed higher betweenness and closeness scores.This suggests that the mental/cognitive self plays a key role in connecting the perception of synchrony and the more cognitive layers of our subjective internal and external perception.

Synchrony of self -Malleability by internal and external factors
Our data show that synchrony consists in the perception of synchrony with both internal (mental self and bodily self) and external (others, environment) features.Do extreme changes in these internal and external features lead to changes in the perception of synchrony?This was probed by investigating the impact of the COVID pandemic on VAS items in subjects that underwent two times testing, before and during COVID (See Table 4).
We observed significant differences in almost all synchrony VAS items after the COVID compared to before COVID.Synchrony with self, body, and environment was significantly lower after the COVID pandemic than before (Fig. 4).In contrast, no significant differences were observed in the VAS items for internal cognition (while the ones for perception of constraints, such as the feeling of encloseness and the reduction of the sense of freedom, increased as expected) (Fig. 4).Together, these findings demonstrate the malleability of the perception of synchrony to xternal environmental events like the COVID pandemic.This suggests environmental sensitivity of perception of synchrony and further supports its internal-external relational character.

Discussion
Conducting a large-scale psychological study, we demonstrate the key role of synchrony in our perception of self with respect to both internal cognition and perception of constraints.Our data on subjective visual analogue scales and psychological self-reports, identify the perception of synchrony with both internal self/body and external others/environment as most basic feature as distinct from internal cognition itself and perception of constraints.Using graph-theoretic measures for network analysis, synchrony of self, together with synchrony with the body, takes on the role as node with high centrality and betweenness within the psychological network of internal-external perception.Finally, the perception of synchrony is malleable to both internal (related to adaptive and maladaptive features of the self) and external (life events like COVID pandemic) factors.Together, we demonstrate the importance of synchrony in the perception of our self on the psychological level which, given recent findings, may be met by corresponding synchronization on the neural level (Raut et al., 2021).Synchrony would then be considered as a shared feature in neural and Fig. 3. Network analysis of all VASA items (Inter-network).
Our main focus was on the subjective perception of synchrony as different from internal cognition and external perception of constraints.We accordingly developed different VAS items subjecting them to principal component analysis.As hypothesized, that yielded a high loading of all VAS synchrony items as distinct from both internal cognition and perception of constraints.Most notably, this included perception of synchrony with self, body, others and environmentthis suggests that the perception of synchrony is not restricted to the own inner mental space of the self but extends beyond to the bodily boundaries to the environmental space.Being based on the perception of synchrony, the self can be considered relational as it crosses the gap of the internal mind and the external world.Such internal-external relational conception of self is well in accordance with models proposed in the recent literature (Craig, 2010;Di Plinio et al., 2022;Kim & Johnson, 2012, 2015;Northoff, 2016;Northoff & Panksepp, 2008;Scalabrini, Schimmenti, et al., 2022;Yeshurun et al., 2021).
The key role of synchrony is further supported by our correlation data with the psychological scales.Synchrony measures largely constituted the first PCA component which showed significant positive correlation with various rating scales related to the sense of self (e.g., interoceptive awareness and self-concept clarity), and relation with the natural environment, identification with nature and humanity.This does not only validate our VAS synchrony scales but also underscores the key role of synchrony in establishing relation  A. Scalabrini et al. with the sense of self, the body, others, and the external environment or nature.Albeit tentatively, we suppose that such relational nature of self can developmentally be traced to mother-infant relationships (Feldman, 2007;Feldman et al., 2011;Feldman et al., 2002) and its impact on self-other relationships in adulthood (Ulmer Yaniv et al., 2021) as described in the introduction.On the other side, synchrony also correlated negatively with rumination, total symptomatology, fear of covid-19 and emotional dysregulation, suggesting how lack of synchrony might represent an internal vulnerability of the self.The network analysis shows some differentiation even within the first PCA component (i.e., the synchrony component).Synchrony with both self and body showed high degree of centrality and betweenness suggesting that they take on the role as node for the other synchrony items including the synchrony to other and the environment.That is well in line with the robust correlation of synchrony especially with the scale for Self-concept clarity and interoceptive awareness (MAIA), which concern mainly the perception of the own body and the own self.The enlarged network analysis shows that synchrony of self, including again synchrony to body, take on a central role for all the VAS items related to the experience of internal cognition and perception of constraints.We consequently assume that the perception of internal-external synchrony of self may constitute a key component for what recently has been described as Fig. 5. Graphical representation of main findings of the study.Synchrony can be conceptualized like one of the core features of the "psychological baseline model", that is related with adaptive and maladaptive features of the self and is malleable to the internal vulnerabilities and external events.
Finally, we demonstrate that perception of synchrony is malleable by external features.Our data show that an external environmental life event like the COVID pandemic induces significant change in the perception of synchrony with self, body, others and environment.After the pandemic, subjects reported to perceive significantly lower degrees of synchronization of their self (e.g., desynchronization) -its role as "psychological baseline" may thus be destabilized by the external threatening events.
Such perception of a desynchronization of self, body, others and environment, in turn, seems to be associated with subclinical behavioral and psychological symptoms comprising Covid-related fear experience (Schimmenti et al., 2020), higher degree of emotion dysregulation (Siegel et al., 2021) and rumination (Satici et al., 2022).Moreover, we also found some gender differences, indeed after the onset of covid pandemic men reported higher scores then women on the experience of synchrony with self, other and body while, on the contrary, women reported higher scores on the experience of trauma, limitation of freedom, feeling of encloseness (Table S2bis).Regarding the psychological questionnaires women reported higher scores then men in connection with nature, identification with humanity, rumination, and fear of covid (Table S3bis).These data are in line with previous findings related to psychopathological manifestations in covid-19 patients showing that females report higher scores in several psychopathological domains over the time (Mazza et al., 2020;Mazza, Palladini, De Lorenzo, et al., 2022;Mazza et al., 2021;Mazza, Palladini, Poletti, et al., 2022;Scalabrini et al., 2023).
In sum, our data suggest how of the degree of perceived synchrony or connectedness seem to constitute characteristic of resiliency vs. vulnerability in dealing with stressful and uncertain moments of life.Thus, the construct of self and psychological baseline, needs to be considered as an adaptive factor that also suggest how promoting psychological and social well-being should target the experience of connectedness/attunement/synchrony as a key factor to better develop coping and resiliency features.
Together, our findings highlight the key relevance of the perception of an internal-external synchrony of our self with body and environment.This is distinguished from the perception of constraints and internal cognition.Albeit tentatively, we might assume that the perception of an internal-external synchrony of self constitutes a psychological baseline or default for both internally-and externally-oriented (Northoff et al., 2022;Scalabrini, Schimmenti, et al., 2022).The key role of synchrony on the psychological level puts the self in line with both neural and biological levels (e.g., brain and biological world).Various findings show that high neural synchronization is related to higher sense of self (Kolvoort et al., 2020;Scalabrini et al., 2019;Scalabrini et al., 2017;Smith et al., 2022;Wolff et al., 2019;Wolman et al., 2023) synchrony may then be shared by neural and psychological levels of self as their "common currency" (Northoff et al., 2020a).Synchrony in this sense is neither special to the self nor the brain though.Synchronization processes are abundant in the biological world where they can be observed in different species like aunts, birds, monkeys and others.Hence, rather than being a special higher-order cognitive process, the self may be mediated by synchrony as a most fundamental and completely non-special biological process that is abundant in the biological world (Fig. 5).

Limitations
Some limitations shall be mentioned.We are aware that VAS questions are subjective and therefore lack the kind of objectivity one would wish for on methodological grounds.However, we showed their correlation with the objective psychological instruments providing some validity.Moreover, another limitation concern that the VAS scales referring to the period defined as "before covid" were administered retrospectively introducing a subjective bias.However, the key target and focus of our study was exactly on the subjective nature of self, that is, the perception of its synchrony and internal cognition by the subjects themselves.For that VAS are ideally suited.We aimed to validate our VAS by psychological rating scales by correlating both.This showed especially correlation of synchrony with those scales that focus on relationship with self-concept clarity, with the body (MAIA), connectedness with nature scale (CNS), and others/humanity (IWAH).Although requiring future more substantial validation, this provided some evidence for the validity of our VAS items.
Our subjects were from a wide range of different countries which introduces cultural differences.While this may be considered a weak factor, we regard it as strength as it really shows the universality of the perception/experience of synchrony of self across various cultures if not the whole world.That further supports the idea of the synchrony as a most basic and therefore universal feature which, as we speculate, puts the human self on a pair with the biological world and its various species.
Finally, we did not include any neuronal measure.Is the perception or experience of synchrony of self on the psychological level accompanied by corresponding synchronization processes on the neuronal level of the brain?Synchronization in neural activity can be measured in both spatial and temporal domains like in network structure and phase-related processes.Are these neuronal measures of synchrony related to the psychological measures of synchrony, that is, perception of synchrony of self as probed in VAS items?In that case, synchrony would be shared by both neural and psychological levels providing their "common currency" (Northoff et al., 2020a).Being potentially common to both, synchrony may then be central in providing transition or transformation of neuronal into psychological or mental activity.

Conclusion
Synchrony is a most fundamental and basic feature in the biological world and thus in nature holding across different species.Does it also apply to our perception of self?Using both subjective VAS and self-report psychological questionnaires, we demonstrate that the perception of an internal-external synchrony of our self with body, others and environment is a most basic fundamental feature of our A. Scalabrini et al. mental life that according to its degree of can be related do adaptive or maladaptive manifestations.The perception of the internalexternal synchrony of self is highly malleable by either internal psychological difficulties or external life events like the Covid pandemic; such malleability of the synchrony of self leads to psychopathological symptoms like depression with rumination, anxiety/ fear, and others.Thus, we suggest that that our self and our degree of synchrony with the body, others and the environment is the psychological component more threatened by an adverse external event (like the COVID-19 pandemic) and, at the same time, the factor more associated with resiliency and coping during such times.Together, we demonstrate the key role of an internal-external synchrony in our perception of selfthis aligns the self with the biological world and nature where synchrony is a most basic fundamental feature holding across different species.

Funding sources
This research was supported by "Search for Excellence -UdA" to A.S. for the project SYNC (The Self and its psYchological and Neuronal Correlates, European Union's Horizon 2020 Framework Program for Research and Innovation under the Specific Grant Agreement No. 785,907 (Human Brain Project SGA2).G.N. is grateful for funding provided by UMRF, uOBMRI, CIHR and PSI.

Declaration of Competing Interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Fig. 4 .
Fig. 4. Graphical plot of VAS significant t-test differences for before vs after covid pandemic.

Table 2
Principal Component Analysis of VAS during covid-19.
VASA = Visual Analogue Scale during pandemic Only values > 0.3 are reported in the tableA.Scalabrini et al.

Table 3
Correlation analysis between psychological scales and PCA components with a 95% confidence interval (CI) based on 1000 bootstrap samples for the bivariate associations.

Table 4
Paired sample t test before vs. after the threat.