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  • Writer's pictureAmos Gdalyahu

We Have Chemistry!

Updated: Jan 9

Sometimes we find ourselves with a potential partner and feel a connection on a different level, something that is difficult to explain in words and feels like a special bond. We say, "We have chemistry," and feel that we understand the phenomenon even though we've only given it a name, perhaps because now when it has a name, it feels clearer. But what does it actually mean to have chemistry? In this post, I will suggest an explanation based on research into the phenomenon and also share my own idea. I'll combine psychology and biology as I like to do. I will start with a background necessary to understand the explanation, then I will present the explanation itself, and will continue with a brain mechanism and with further expansion of the idea. Let's get started!

Background Attachment figures - parental relationship and romantic relationship Humans belong to the minority of mammals (about 5%) that form pair bonds. The bond can last a lifetime with sexual exclusivity, it can be for some period, and it can exist without sexual exclusivity. The main point is that humans form relationships. The other 95% of mammals, go their separate ways after sex, the mother raises the offspring alone and there is no connection between the parents. However, you may have noticed that I mentioned here another type of bond: the bond between the mother and the offspring. The mother takes care of them for food, protection and invests many resources in her offspring. The offspring, for their part, when they are in distress, call the mother for help. That is, even when there is no pair bond between the parents, there is a mechanism in evolution that causes bonding, the bond between the mother and the offspring

In humans and monkeys, this bond is crucial for proper development. It is not enough to provide babies milk, food, and water. Without a personal connection that also involves gentle and warm touch, humans (and monkeys too) develop severe physical and psychological problems. Touch is thought to provides a sense of security, as demonstrated in Harry Harlow's studies in the 1950s-1970s (1). During that time, parents were actually advised to minimize physical contact with their children (!) due to fear of infections. It was only in the 1970s, following these studies, that the policy towards touch with children changed. The point is that babies and toddlers need human touch, the need for touch is a need for connection, and beneath the need for connection lies the attachment system. I wrote in detail about the attachment system here and now briefly: the attachment system causes the offspring to look for the mother in times of distress in order to receive security from her, and for the mother it causes a desire to care and help the offspring. In humans, ideally, the baby learns that his mother (and father) will help him when he is stressed and thus develops a secure attachment pattern with a sense of self-worth and trust in others. In nature, all the mother's efforts would be in vain if she were left alone. In an environment with many predators, or when you have to invest a lot of energy in bringing enough food, the mother alone will reach exhaustion and she needs help otherwise the offsprings will die. Under these conditions, every time anew, the relationship between the parents and also the paternal relationship developed in evolution. These connections allow the offspring to survive. How did this happen? The idea is that since there was already a system in the brain that allowed attachment between the mother and the offspring, nature repurposed it. That is, nature used a system that knows how to create a relationship (mother-offspring) to create a relationship between the parents and between the father and the offspring. That is, our attachment to our romantic partners is based on a mechanism that was shaped when we were babies while our parents took care of us and which is the same mechanism that allows us to take care of others. How does it work biologically? If the basis of romantic attachment and mother-offspring attachment is the same, then it makes sense that the mechanism in the brain is very similar. In 1980 during the birth of her eldest son, Prof. Sue Carter was flooded with feelings of love for the baby. Being a scientist, an idea flashed in her mind: she knew that the hormone oxytocin is secreted in large quantities during childbirth, it contracts the muscles of the vagina and uterus and thus speeds up the birth. Therefore, she speculated that if a bond forms between the mother and the baby after birth due to the action of oxytocin, perhaps oxytocin is also secreted during sex and facilitates the bond between sexual partners (2)? It was a guess but since then it has indeed turned out that the hormone oxytocin is secreted during sex and is indeed associated with the formation and maintenance of both the pair bond as well as the parental bond. I will mention oxytocin again later after I write about another possible basis for the attachment system: synchronization. Synchronization is also found between parents and babies and between spouses (3,4). It is possible that synchronization creates and preserves the bond between parents and offspring as well as the romantic bond, like oxytocin. In fact, synchronization and oxytocin will meet shortly, be patient. So what have we had so far: Our parents and romantic partners are attachment figures, that is, figures we trust to help us when we are stressed so that we can gain security and go out to explore the world. Prof. Gorit Birnbaum from Reichman University claims that passion is actually an internal barometer for the strength of the belief that the partner is an attachment figure (5), that is, a figure of support for us. At the beginning of the relationship, there is nothing that disproves this belief, and therefore the passion is very strong, later there is already (...) and the passion apparently decreases. But as long as basically the belief exists - the passion is there, and it will connect the couple during a crisis. A marital crisis will end in a 'make up sex' and a crisis outside the relationship leads to the desire to get closer to the partner. As in childhood we received the security from the presence of the parents, the first attachment figures, in adulthood partners become attachment figures that give us security. Adults like children are reassured by the attachment figures Proximity to attachment figures gives us confidence and directs cognitive resources to other tasks. That's why when the families join exhausted fighters at the end of their trainings the fighters get renewed strength, that's why people in a hearing test hear better (!) when they look at a picture of their attachment figures (6), that's why children do better in baseball when the parents are looking at them than when the parents are present but are absorbed in their phones (7), that's why when one of the partners goes through a crisis they need the presence of the other and that's why the loss of an attachment figure (bereavement or romantic breakup) is likely to cause cognitive decline. So how does it happen? How do relationships translate to biology? Let's start with parent-child relationships and then move on to romantic relationships. Synchronization between the parents and the baby Synchronization in behavior As mentioned, the basis of the romantic relationship is the attachment system created at the beginning for a maternal relationship. The baby's survival depends on who cares for it. Before the baby has language, he has to communicate his needs in another way and equally the caregivers cannot tell the baby to calm down, but have to convey the message in non-verbal ways. Little by little, the baby associates the parents' behaviors with relaxation and security. One of the most prominent things in the relationship between parents and babies is the synchronization. The parents and the baby imitate each other's facial expressions, they exchange glances, they pay attention to the same things "Look, a cat!", the adults start talking in the intonation of toddlers and sometimes with the same body posture and the toddlers in turn imitate the parents. A mutual relationship is created that gives satisfaction to both sides. Physical synchronization (autonomous, involuntary) Not only the voluntary behavior is synchronized: surprisingly it turned out that the involuntary biology is also synchronized! Prof. Ruth Feldman from Reichman University showed a match in heart rate and blood hormone levels (cortisol, oxytocin, CCK) between parents and their children. This is surprising because how does the parent's body know what the baby's heart rate is? And how does the baby know the level of cortisol - the stress hormone - in the parent in order to adapt to it. In fact, as far as I know, there is no answer to this, but the findings that the phenomenon itself exists are strong. The involuntary physical adjustment may be as a result of an emotional adjustment. That is, the behavior of a stressed parent causes the baby to be stressed and therefore both will have high cortisol levels. When the baby is in distress, he cries and this causes distress in the parent. Such a mechanism is actually a mechanism of empathy: when one hurts, then the other hurts too. This is how the parent feels what the baby feels even without language. Later in the post we will see a possible brain mechanism for this. But I'll just mention that Prof. Feldman also showed that the level of synchronization between parents and toddlers correlates with the amount of oxytocin in the parents (8), which raises the possibility that oxytocin increases interpersonal synchronization. Indeed, other studies support the idea that oxytocin increases synchronization between people (9-11) (perhaps helping this is the fact that oxytocin makes people look into each other's eyes (12)). This observation actually unites the two ideas: oxytocin increases synchronization and thereby strengthens interpersonal bonds. I'll come back to the mechanism - that is, how it happens - later, the important point right now is that the parents and the baby are synchronized with each other in their behavior and biology. I'm done with the background and now, finally, I can explain: What does it mean that "we have chemistry"?

Since the parents are in sync with their baby, I suggest that the baby learns to associate the attachment figure with a figure that is in sync with him. In other words: as far as the baby is concerned, 'a figure that is synchronized with me is my attachment figure'. This learning stays with us, therefore when we are adults and meet a potential partner and they are also in sync with us, because of the association we learned in childhood we believe they will be attachment figures for us, and an attraction is created . As the attachment figure gives security, a figure that is in sync with us gives us security. We are not aware of all this and just feel that we have chemistry. Implications and Extensions If this explanation is correct, synchronization between potential partners increases attraction. Is this really happening?

Romantic attraction and synchronization

The video on the computer screen in the lab showed a couple on a blind date: Danny, a handsome guy, leaned back and put his hands on his hips. He looked at Helen's beautiful red hair sitting across from him, as she leaned forward, her hands on her glass of wine and looking into his eyes. The researcher already knew the answer and yet she looked at another screen, where there was a graph that displayed Danny's and Helen's skin conductance throughout the session. Danny's skin conductivity went up and down - and so did Helen's - but there was no match between the two lines. When Helen's skin conductivity increased for Danny's skin conductivity sometimes there was no change, sometimes there was a decrease and sometimes an increase and vice versa. In other words, both body language and skin conductivity were out of sync between Danny and Helen and the researcher pointed out dryly "she won't want him". An hour later, when Helen was asked who she would choose for another date from the series of men she had met in the experiment, she did indeed choose Jimmy a slim man who apparently looked less attractive than Danny. However, the researcher was not surprised because on Jimmy and Helen's date, their body language was synchronized: they both touched the wine glass at the same time, they exchanged glances and then a smile and also their skin conductivity was coordinated. This is a story I made up to illustrate such an experiment conducted by Prof. Shir Atzil from the Hebrew University, Israel (13). According to synchronization in body language (where people look, their body posture, their hand placement) which is under conscious control, and according to biological synchronization in skin conductance, which we cannot consciously control, it was possible to predict which couples would want to continue to another date and which ones would not! Previous studies have also found similar conclusions: synchronization predicts a desire for closeness (14,15) and vice versa: emotional closeness leads to synchronization. In contrast, potential or existing partners who are not synchronized feel distance and less attraction. Synchronization is also tested by the rate of approach: does one partner try to approach faster than the other want? In that case he will be perceived as aggressive. too slow? In that case he will be perceived as insecure and boring. Exactly at the right pace for both? Walla! Bingo. There is chemistry. I mention this because in reality, we can rely on body language, on intonation, on biological processes to get feedback on how close the other party wants to get. According to the feedback we receive, we can adjust ourselves to each other and maintain synchronization. However, these things are obviously missing in online communication, so I think the success of online dating will be less than face-to-face dating. Synchronization refers to the coordination of processes that take place over time, but it is possible that we generalize it so that not only synchronization but similarity in general creates closeness: "You are also from West L.A? I am too!", or "I also love George Harrison!".. Prospects partners are often trilled to find commonalities. In other words, it may be possible to explain in that way the idea that 'like attracts like'. How do we do it?

Some of you are already thinking practically now, about specific partners you want. You understand that in order for them to want you too, you need to be in sync. But how do you do it? I mean what helps us synchronize? Two people can synchronize with each other according to an external rhythm, for example go dancing, or go to a concert. In other words, music synchronizes people thanks to the rhythm. Another way to achieve synchronization is through the practice of joint breathing, as done in tantric practices, where individuals also sit in excellent symmetry while looking into each other's eyes. In the same way, shared emotions also synchronize us, for example when we watch a movie together, or go to a theater together which are known couple activities. In general, joint activities, a trip for example, do the trick and sync. The message is not only to be together but to do together. Individual close synchronization not only in a relationship Behavioral synchronization between people brings them together not only under romantic circumstances. Turns out, that in general synchrony brings people together and form groups: worship, rituals ceremonies and prayers include a rhythm and they synchronize those involved, and by that throughout history they formed tribes and communities. One can also think of the fondness of army's generals for order exercises in the same way. Also, think of laughter, it is contagious, synchronizes people and consolidates the group. Think of one person who doesn't laugh when everyone around is laughing: he is immediately perceived as not belonging. Indeed, one of the things that people frequently say is important to them in a partner is a sense of humor. This may be the reason. Laughter synchronizes us. In groups, like between romantic partners, as synchronization in behavior develops the group syncs biologically! When there is more biological synchronization (for example in heart rate) there is more feeling of group cohesion (16). In addition, actors, musicians and dancers know a state of flow in group-improvisation. It happens when they achieve superb coordination between them, and they sometimes call it 'To be in the zone'. It's a pleasant feeling of togetherness, dissolution of interpersonal boundaries and it is also accompanied by... biological synchronization (17), yup. Another example of biological synchronization and attachment is mental therapy. It turns out that in therapy a synchronization develops between the therapist and the patient, and oxytocin helps this (18) supporting the view that oxytocin acts through increasing inter-personal synchrony. Moreover, experienced therapists synchronize better than new therapists (18), which shows that the ability to synchronize is learned and that that ability can be developed throughout life even if we are not aware of it at all. So the conclusion is that synchronization does bring adults together. Therefore it's likely that when we say we have chemistry we are actually experiencing interpersonal synchronization. How does the brain understand that there is synchronization? How does the brain create synchronization? As far as I know, there is still no complete answer, but in the next section I will state what is known.

Synchronization in brain activity

Romantic partners synchronize in their behavior and they also synchronize in things that are out of their control such as hormones level, heart rate and even in their brain waves (19)! The brain waves themselves are created from synchronized neural activity within each brain. Apparently the hormone oxytocin helps interpersonal synchronization not only between parents and babies but also between adults (9-11). But how can brains synchronize with each other? A recent study from UCLA done in pairs of mice (20) found neurons in the brain whose activity reflects the activity of the mouse itself and other neurons in the brain whose activity reflects the behavior of the other mouse that is nearby. Thus the two mice synchronize with each other at the brain level even when they perform completely different actions. For example, let's say that mouse A grooms his mustache (his whiskers). He has nerve cells in his brain that immediately start to act because they reflect this behavior. Mouse B also has nerve cells that immediately start to act because they also reflect grooming of mouse A. Therefore, when mouse A grooms his whiskers, he has neurons that their activity reflects that, and mouse B also has neurons that reflect that, so that both mice have neurons that are synced to the grooming done by mouse A. The synchrony the researchers found was associated with non-sexual behaviors so it appears brain synchrony is a general feature of social behavior beyond the romantic realm. By the way, it turned out that the degree of dominance determines the degree of synchronization: dominant mice had more cells that reflected their own behavior and less of the non-dominant mouse. In any case, the presence of nerve cells that encode the other's behavior allows a mechanism in the brain for involuntary emotional and physical synchronization, such as heart rate and hormone secretion. This is a beginning of an answer but there are still many unanswered questions: how do we synchronize when there are many people around, why is it easier for us to synchronize with some people than with others? (I'm guessing that perhaps we have a certain range within which we can move to synchronize (lets' say in heart rate) and therefore we can only synchronize with those within this range, for example if I am emotionally cold and inhibited I can synchronize with someone who is a little excited but not with someone who is in an emotional storm). In another study (21), also from UCLA, the researchers artificially synchronized the brain activity of two mice from a group of 4 mice and then found that the mice whose brains were synchronized preferred to be with each other! Again, this reinforces the message of this post: Synchronization in brain activity causes attraction. The success of the artificial brain synchronization was so amazing, almost unbelievable, that the researchers kind of 'hid' it in the article and highlighted the achievement in the development of the technology itself. Many people myself included are waiting to see if it will be possible to repeat the results of this research. (BTW - try to guess in which university I did my post-doctorate research!)

Sync and Sex Synchronization is a difficult task and the ability to synchronize may indicates the other person's fitness. In order to synchronize, it is necessary to pay attention to the other person's rhythm, as well as to one's own rhythm, keep the rhythm, make adjustments and find the 'right' time for a rhythm change, otherwise there is habituation and boredom. Therefore, it is possible that the one who manages to synchronize and also remain interesting is an evolutionary preferred partner (22). I have already written about synchronization and attraction before contact is made. Once the interaction becomes physical, the kiss can also be a barometer for synchronization. Moreover, making love is characterized by rhythm and interpersonal synchronization that is increasing. As in music and dancing I mentioned earlier, also in sexual relations the sensual body rhythm synchronizes the partners and in addition it synchronizes their brains. Moreover, intercourse is a situation in which people are more focused on the here and now and their attention is directed to the senses more than in any other activity (23). In such a state, which is a state of flow, the ego is reduced and synchronization happens automatically without thought. Thus, a rhythm of movements creates a rhythm of sensations that can create a brain rhythm that gradually increases in brain activity until states of ecstasy (22). Indeed, neural activity across the brain reaches a peak of activity during orgasm similar to an epileptic attack (24). The more attention is paid to the senses, the more the ego disappears (a flow state) and there is more the feeling of merging with the other person who is in sync with us, the dissolution of interpersonal boundaries and an ultimate sense of closeness. Indeed, both men and women who frequently experience orgasm at the same time as their partner also report more sexual satisfaction, more general satisfaction with the relationship and generally more satisfaction with their life (25) Summary Romantic partners are attachment figures. I suggest that as children we learn that our attachment figures are in sync with us and therefore as adults when we meet someone who is in sync with us there is attraction and a feeling of chemistry. The synchronization is in voluntary behavior and surprisingly also in the action of the involuntary systems: the autonomic nervous system (which controls among others heart rate and skin conductance), in the hormonal system and even in brainwave synchronization. Apparently the synchronization is achieved thanks to cells in the brain whose activity reflects the behavior of the other. Synchronization creates closeness (26) and closeness further increases synchronization, which is most pronounced during sexual activity. In sexual activity, the rhythm is reflected in in brain activity that is more and more synchronized in each of the brains with itself, and between the brains involved. This creates - in peak situations - a trance state and a feeling of self dissolution. We have chemistry.


I thank Prof. James Pfaus from Charles University in Prague for sharing with me his thoughts and vast knowledge about everything sexuality including this subject.


  1. “Love in Infant Monkeys”, Harry Harlow, (1959) Scientific American.

  2. “The Monogamy Paradox: What Do Love and Sex Have to Do With It?” Carter, C. Sue, Perkeybile, Allison M. (2018) Frontiers in Ecology and Evolution

  3. “Parent-infant synchrony: a biobehavioral model of mutual influences in the formation of affiliative bonds”, (2005) Feldman, Ruth, Monographs of the Society for Research in Child Development

  4. “The Neurobiology of Human Attachments”, (2017) Feldman, Ruth, Trends in Cognitive Sciences

  5. “Evolved to be connected: the dynamics of attachment and sex over the course of romantic relationships”, (2019) , Birnbaum, Gurit E. Reis, Harry T. Current Opinion in Psychology

  6. “Safe and Sound: The Effects of Experimentally Priming the Sense of Attachment Security on Pure-Tone Audiometric Thresholds Among Young and Older Adults” (2022) Psychological Science, Nagar, S., Mikulincer, M., Nitsan, G., & Ben-David, B. MStupica, B. (2016).

  7. “Rounding the bases with a secure base.” (2016) Attachment & Human Development. “Social Support and the Perception of Geographical Slant” (2008), Journal of Experimental

  8. “Oxytocin and vasopressin support distinct configurations of social synchrony”, (2014), Apter-Levi, Yael, Zagoory-Sharon, Orna, Feldman, Ruth, Brain Research

  9. “Oxytocin improves synchronisation in leader-follower interaction”, (2016), Gebauer, L., Witek, M. A.G., Hansen, N. C., Thomas, J., Konvalinka, I., Vuust, P. Scientific Reports

  10. “The oxytocinergic system mediates synchronized interpersonal movement during dance” (2019), Josef, Liad, Goldstein, Pavel, Mayseless, Naama, Ayalon, Liat, Shamay-Tsoory, Simone G. Scientific Reports

  11. “Oxytocin enhances inter-brain synchrony during social coordination in male adults”, (2016), Mu, Yan, Guo, Chunyan, Han, Shihui, Social Cognitive and Affective Neuroscience

  12. Oxytocin Increases Gaze to the Eye Region of Human Faces, (2008), Guastella, Adam J., Mitchell, Philip B.,Dadds, Mark R., Biological Psychiatry

  13. “Bio-behavioral synchrony is a potential mechanism for mate selection in humans”, (2022), Zeevi, Lior, klein Selle, Nathalie, Kellmann, Eva Ludmilla, Boiman, Gal, Hart, Yuval, Atzil, Shir, Scientific Reports

  14. “You are in sync with me: Neural correlates of interpersonal synchrony with a partner”, (2014) Cacioppo, S., Zhou, H., Monteleone, G., Majka, E. A., Quinn, K. A., Ball, A. B., Norman, , G. J., , Semin, G. R., Cacioppo, J. T. Neuroscience

  15. "Being on the same wavelength: Behavioral synchrony between partners and its influence on the experience of intimacy", (2019), Sharon-David, Hilla, Mizrahi, Moran, , Rinott, Michal, Golland, Yulia, Birnbaum, Gurit E., Journal of Social and Personal Relationships

  16. “Interpersonal Physiological Synchrony Predicts Group Cohesion”, (2022), Tomashin, Alon, Gordon, Ilanit, Wallot, Sebastian, Frontiers in Human Neuroscience

  17. “Being in the zone: Physiological markers of togetherness in joint improvisation”, Noy, Lior, Levit-Binun, Nava, Golland, Yulia, Frontiers in Human Neuroscience

  18. “Inter-brain plasticity as a biological mechanism of change in psychotherapy: A review and integrative model”, (2022), Sened, Haran, Zilcha-Mano, Sigal, Shamay-Tsoory, Simone, Frontiers in Human Neuroscience

  19. “Human attachments shape interbrain synchrony toward efficient performance of social goals”, (2021), Ruth Feldman, NeuroImage

  20. “Correlated Neural Activity and Encoding of Behavior across Brains of Socially Interacting Animals”, (2019), Kingsbury, Lyle, Huang, Shan, Wang, Jun, Gu, Ken, Golshani, Peyman, Wu, Ye Emily, Hong, Weizhe, Cell

  21. “Wireless multilateral devices for optogenetic studies of individual and social behaviors”, (2021) Yang, Yiyuan,Wu, … Rogers, John A. Nature Neuroscience

  22. “What is orgasm? A model of sexual trance and climax via rhythmic entrainment”, (2016), Safron, Adam, Socioaffective Neuroscience & Psychology

  23. “A Wandering Mind Is an Unhappy Mind”, (2010), Killingsworth, Matthew A., Gilbert, Daniel T., Science

  24. “Brain Activity Unique to Orgasm in Women: An fMRI Analysis”, (2017) , Wise, Nan J., Frangos, Eleni, Komisaruk, Barry R.

  25. "Simultaneous Penile–Vaginal Intercourse Orgasm is Associated with Satisfaction (Sexual, Life, Partnership, and Mental Health)", (2011) Brody, Stuart, Weiss, Petr, The Journal of Sexual Medicine

  26. "Being on the same wavelength: Behavioral synchrony between partners and its influence on the experience of intimacy", (2019), Sharon-David, Hilla, Mizrahi, Moran, Rinott, Michal, Golland, Yulia, Birnbaum, Gurit E. Journal of Social and Personal Relationships

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Kedem isabel
Kedem isabel
Apr 23

היי חברים, אני אנה קדם, אני חדשה פה אני לא יודעת איך הדברים עובדים פה, אבל קראתי פה תגובות טובות ואוסיף קצת מהחיים שלי כי זה יהיה שימושי עבור רבים אנחנו כאן, מחפשים תשובות ומערכות יחסים לפתרון בעיות. הייתי במערכת יחסים עם סמול ארבע שנים, הוא נפרד ממני, עשיתי הכל כדי להחזיר אותו, אבל הכל היה לשווא, כל כך רציתי אותו בגלל האהבה שיש לי לבעלי, ביקשתי ממנו על כל מה שהבטחתי, אבל הוא סירב. הסברתי את הבעיה של מערכת היחסים שלי עם עמית לעבודה והיא הציעה לי לפנות אל מטיל אהבה שיוכל לעזור לי לעשות כישוף אהבה כדי לקבל גבר הביתה, אבל אני אישה שמעולם לא האמינה בקסם, היה לי אין ברירה, ניסיתי, יצרתי קשר עם מטיל כישוף והוא…

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