Where do intense feelings come from?
The most important role in the generation of passion and intense romantic feelings is given to dopamine, writes Semir Zeki, professor of neuroscience at University College London. By acting on certain receptors in the brain, this neurotransmitter motivates us to fulfill our desires and achieve goals - usually they are associated with something useful for life. For example, with reproduction (respectively, the desire to get the object of passion) or with the acquisition of new knowledge, impressions, experience: the better you know the situation and the more you know how, the higher the chances of survival.
Dopamine is also associated with the joy of new experiences, travel, overcoming danger, the desire to grow in salary and my desire to complete this article. Dopamine receptors D2 are responsible for our love impulses - they are backed up by D1, which block interest in other potential partners.

So, we abandon friends, lose productivity, can't tear ourselves away from each other, orgasms darken our eyes. But this is temporary.

Why feelings get cold
Over time, the sense of novelty fades. And also a familiar partner is always at hand - there is no longer a need for dopamine motivation to win him over. This neurotransmitter, of course, continues to be released, but not in those quantities.

As a result, passion fades somewhat, feelings are no longer so burning, and someone may even be drawn to flirt with someone else.

Leading sex training speculate on this topic, calling to play inaccessibility. There is some truth in these words, except that in close relationships you usually don’t bother and don’t arrange an obstacle course on the way to the bedroom.

It is important that dopamine-induced activity in some areas of the brain is associated with a decrease in the work of others: for example, the ability to critically evaluate a partner is drowned out. When the love euphoria passes, you yourself know what happens.

How love changes over time
If the subsided dopamine wave did not expose a pile of garbage on the shore from misunderstanding and disappointment, then it makes sense to talk about vasopressin and oxytocin. They are your invitation cards to a cozy family life.

These social molecules form kindred warmth, tenderness, give a sense of calm and security next to loved ones. Oxytocin is released at the dating stage, plays a big role in the formation of attachment and, unlike dopamine, does not leave you after a year of relationship.
Oxytocin is especially active in women (it is associated with maternal feelings and is involved in lactation), and in men, vasopressin, which is chemically similar to it, plays a large role. It forms paternal feelings and “turns on” care, as well as aggression towards other contenders for a partner. The feeling of vasopressin ownership is also familiar to women, albeit to a lesser extent.

A strong surge in oxytocin and / or vasopressin is detrimental to dopamine, according to Daniel Lieberman, a psychiatrist and author of Dopamine: The Most Needed Hormone. This is partly why immediately after the birth of a child, you usually do not really want sex. But a moderate concentration of these substances just contributes to the release of dopamine, which is associated with arousal, notes Rutgers University anthropologist Helen Fisher.

In long-term relationships, areas of the brain associated with sympathy are also activated. They also rely on friendship, which is accompanied by the release of opioids and endorphins (they act on opioid receptors).

Like vasopressin and oxytocin, in moderate amounts, these substances additionally activate dopamine (and with it sexual desire). Therefore, strong friendship is a component of passion. And also loyalty. According to a paper by Oklahoma State University researchers, friendship-related opioids appear to lower testosterone levels in both, but especially in men because they naturally have more testosterone (vasopressin and oxytocin, by the way, have a similar effect). Meanwhile, this hormone is tightly intertwined with sexual desire and supports the desire to find someone to continue the family. Those who are in successful relationships, and even more so raising children, have lower testosterone levels than those who are single.

But in men (less often in women), who lack something in the family, testosterone rises, they begin to desire intimacy more. And given that not everything is fine in a relationship, they often resort to connections on the side, experts conclude.

This should not be taken as an excuse for cheating.

In the end, well-married and married people can cheat with low testosterone, and the owners of its high concentration can still be faithful. Because cheating is primarily a choice, not biology.

What keeps long-term love
Apparently, it is thanks to friendship that science knows people who celebrate a pink wedding in a kind of dopamine euphoria. A group of scientists from the already mentioned Rutgers University studied couples who retained years of love and passion almost in its original form, and analyzed their relationship. It turned out that the partners were connected by close friendship and the ability to influence each other's personal growth through it.

This implies not just a comfortable existence, but the presence of common interests, views, the desire to do something together, to develop in one direction.

The logic is simple: the many pleasant, interesting, and rewarding things you can do with a like-minded partner contribute to the release of dopamine that causes passion. He's usually fun to be around too.

How common hobbies are transformed into desire
According to the two-factor theory of emotion and excitatory transfer theory, the brain has an interesting tendency to interpret average sensations in intensity depending on the context. This was first proven in an experiment with two bridges. Two groups of men walked on different bridges: stable and shaky. Both there and there the participants were met by an attractive girl who asked questions from the questionnaire and left her number. The men who met the girl on the dangerous bridge called and made appointments more often.

Researchers believe that in a relatively safe situation, the brain is able to take a slight fright for excitement (if there is someone exciting nearby) and gladly spend the produced dopamine on it. This may work with other stimuli and neurotransmitters as well.

In another experiment, subjects from different groups first received physical activity - light, medium and strong - and then watched erotica. The members of the second group got excited the fastest. The remnants of excitement caused by sports, at the opportunity, were transformed into sexual desire.