We know that whether or not we find someone attractive is determined by many psychological, social and cultural factors. But in order for those “sparks” to fly between two people a whole system of internal biochemical processes has to take place in a precisely specified order.
Love is the dream of the unhappy, inspiration of the poets and a big unknown for many scientists, from psychiatrists, through philosophers, to biologists. Let us now take a look at what can be studied empirically, in other words – love from the perspective of molecules. After all, each human is composed of approx. 7,000,000,000,000,000,000,000,000,000 (7 quadrillion) atoms and their combinations surely are important.
By observing processes that take place in humans when they fall in love, we can say that it looks like a chemical and biological chain reaction composed of many elements. Whether or not we find someone attractive is influenced by a vast number of psychological, social and cultural factors, and it is hard to specify strict rules that would apply to all of us. Nevertheless, according to Mark B. Kristal, professor of psychology from the Buffalo University, there are certain groups of biochemical compounds necessary for infatuation, and for two people to fall in love requires a whole system of external stimuluses and internal biochemical processes—all happening in the precise order. It all starts with the smell. What really matters is our natural scent, and pheromones hidden in it are most probably scent-free. The existence of pheromones in humans has not been scientifically proved yet but we know quite a lot about those excreted by animals and insects.
Pheromones are a mix of different chemical factors used for communication. Depending on their composition, they may serve as a way to attract a potential partner or a means for scare off a potential rival. In humans, these flying molecules excreted from different glands reach the nose, where they come across a very sensitive vomeronasal organ. This, in turn, activates the hypothalamus, a small portion of the brain, and if everything “matches”, we begin to take interest in our partner and our grey cells begin to glow during positron emission tomography (PET).
Using positron emission tomography, a brain activity imaging technique, Dr Richard Davidson from the University of Wisconsin-Madison managed to discover a part of the brain now considered the “love centre” — the already mentioned hypothalamus, a part of the forebrain which belongs to the limbic system, a set of the oldest brain structures. This area regulates various metabolic processes and many functions of the nervous system. It is also where the love chain reaction takes place when Cupid arrow strikes. When hypothalamus receives a signal showing that the person we smell might be a potential partner, it starts to excrete a neurotransmitter called phenethylamine (PEA). Increased level of PEA in the brain manifests itself, on the one hand, with happiness (sometimes inexplicable), self-confidence, excitement, overactivity, and problems with concentration. On the other hand, it leads to insomnia, eating disorders, breathlessness, and sometimes anxiety or depression. It is a state similar to what drug addicts often feel. This is due to the fact that PEA belongs to the group of amphetamines. No wonder that in popular culture phenethylamine is called „the love drug” and people, who fall in love act as if they were on amphetamine all the time and are uncritically enchanted with that other person.
But this is not all. Increased level of PEA results in more changes, such as higher excretion of noradrenaline, a hormone also known as the “substance of love” — a neurotransmitter, whose effects has not been fully confirmed yet. We do know that it works similar to adrenaline: when Romeo-to-be sees his beloved, his blood pressure goes up, his heart races, level of glucose in blood increases and his appetite shrinks. His Julia, on the other hand, blushes (as her facial blood vessel contract). Both people experience better blood flow, especially around clitoris and penis, and increased touch sensitivity. Now, the state of being completely carried away expands to the whole body and is visible for others.
As the level of noradrenaline goes up, another substance is released. This time it is dopamine, the happiness hormone, which completely affects the rest of our senses and body parts so far uninvolved in our “falling in love”. Dopamine affects brain processes that control movement and body activity, as well as the ability to express pleasure. We are familiar with this neurochemical because its level increases always when we get excited about a new gadget, a beautiful dress or a gift that is yet unpacked. We also “feel” it prior to receiving a prize – both material and emotional – as it affects our emotional response. That is why it is also referred to as the “reward pathway”. Dopamine makes us love someone “until death tear us apart…”
The second part of this duet is serotonin. When dopamine level increases, the amount of serotonin is substantially reduced. Normally, serotonin gives us good sleep and the feeling of calm but when its level is too low, it affects the nerve cells communication resulting in general absent-mindedness and concentration problems. A person struck by Cupid’s arrow becomes unfocused, prone to mood swings and at the same time waits impatiently for the next meeting with their second half as if they were waiting to collect their lottery prize.
All these four neurotransmitters make us crazy in love and happy to be in a relationship. The key substance here, however, is phenethylamine as it controls all the levels of the remaining three. Unfortunately, it doesn’t work indefinitely. As PEA is a drug derivative, after some time human body becomes resistant to it. Research shows that somewhere between 18 and 48 months (four years) into a relationship, peoples’ brains become resistant to PEA, and their flame of passionate love slowly burns out and becomes weaker. This is when infatuation or enchantment may end and the relationship enters a completely new phase.
High level of dopamine also causes the release of oxytocin and vasopressin, hormones which have a similar structure but different effect. They are found mainly in the brain but also in ovaries and testicles, and in a somewhat magical way they always act in moments very important for humans. Women have more oxytocin receptors, which become activated by touch, fondling and during orgasm. This hormone reduces stress, lowers blood pressure, reduces pain and helps to relax. It also causes uterine contractions during labour and is responsible for lactation when a woman breastfeeds. In men vasopressin dominates, which is released due to testosterone and erection. Its effects are similar to those of adrenaline: excitement, blood vessels contractions, higher blood pressure as if the body was getting ready for a fight, escape or sexual intercourse. Interestingly, its amount increases the higher the stress level is. High amount of vasopressin in a man results in his strong attachment to his partner, the need to look after her and remove potential rivals.
In both partners, increased levels of the above-mentioned hormones results in the feeling of relaxation, calm, attachment and mutual acceptance, and therefore they are directly linked with shaping of mature love in a relationship.
Over time, when the amount of PEA decreases, the endorphins—which up to now have been suppressed—enter the game. Endorphins are a group of hormones that have a similar effect to morphine: they generate feeling great about oneself and suppress any signs of anxiety and pain. Like gentle creatures, endorphins can move around our body for years stimulating deep feelings for our partner. So despite initial highs, our brain tries to work for the benefit of our relationship—after all we all want to be happy ever after. This is where this chemical and biological love reaction chain ends. We can compare it to a pile of wood that is covered with petrol before being set on fire. At the beginning, a single spark is enough for the whole thing to go off, flare up and keep burning. After such a striking start as the time passes the fire dies down a little bit but still burns and to prevent it from dying down completely we need to fuel it with the right substances. Science measures the presence of majority of these “love substances” forming a molecule cocktail in nanograms, i.e. one thousand-millionth of a gram. See how tiny love really is?
Date of publication: 1 February 2016
The article was published in Newsweek Nauka