Neurochemistry of Love: Molecular Mechanisms of Human Attachment and Relationship Dynamics

In all its manifestations, love is one of the deepest experiences of humanity, but it is also based on the neurobiological processes that can be measured. Scientific studies of love have advanced in leaps since the seminal work by Fisher, who suggested that there are different systems in the brain that are used to attract, romantically love, and attach [1]. Modern neuroscience also discloses how what poets have been explaining or raving about over thousands of years concerns the heart; it is actually complicated neurochemical activity coordinated by the brain. In evolutionary terms, romantic attachment capabilities provided significant adaptive benefits. The pair-bonding also enabled biparental care, a higher survival rate of the offspring, and the formation of social structures, which improved cohesion of the groups. The neurochemical pathways of these behaviours are strikingly similar across mammal species, indicating ancient evolutionary roots. An example of this is prairie voles, which have been an essential animal model for studying monogamous pair-bonding because of close neurochemical parallels of their attachment mechanisms with human attachment mechanisms [2]. In this review, the molecular mechanisms that govern human romantic relationships have been reviewed in an integrated approach, and how neurotransmitters, neuropeptides, and hormones interplay to generate the subjective experience of love as well as stimulate the attachment behaviours. We also take into consideration the effect of individual differences within these systems, which can explain the difference in attachment styles and relationship outcomes.

The Three-Phase Model of Romantic Love

Fisher and colleagues hypothesized a theory of romantic love according to which there are three neurobiological systems, but each is separate yet tied to each other: lust, attraction, and attachment. All the stages have various neurochemical profiles and play different functions of evolution.

Lust: The Foundation Phase

Sexual desire or lust is mainly determined by sex hormones, which are present in both males and females, though in varying quantities, i.e., testosterone and estrogen. These hormones act on the hypothalamus and lead to the desire of attaining sexual satisfaction. The sexual desire level is intertwined with the level of testosterone, and it has been shown that testosterone can be used to boost libido in males and females. But lust in itself is not sufficient to explain partner preference or selective bonding and involves other neurochemical systems [3].

Attraction: The Romantic Love Phase

The attraction phase, which is full of excessive attention to a particular person, euphoria when being together with the person, and intrusive thinking about the beloved person, is found to have a particular neurochemical profile. The study findings of functional magnetic resonance imaging indicate that people who look at the pictures of romantic partners experience greater activation of the areas of the brain containing dopamine, especially the ventral tegmental area and caudate nucleus, which are related to reward processing and motivation [4]. Dopamine is very critical during this stage. High doses of dopamine create exhilaration, energy, concentration, attention, and drive to seek pleasures—all the traits of early romantic love. The dopaminergic reward system generates some positive reinforcement to the closeness of the romantic partner, like the processes that take place in addiction. This analogy is the reason why romantic love is capable of causing dependency-like symptoms, such as tolerance, withdrawal, and relapse patterns. Interestingly, these people in early-stage romantic affection demonstrate a reduction in serotonin levels, similar to that of the case of the obsessive-compulsive condition. This decrease can explain the intrusive, obsessive thinking of the beloved that is a feature of new relationships. Also, the levels of norepinephrine rise when one feels attraction, which adds to arousal, a rapid heart rate, and physiological thrill that is caused by romantic interactions [5].

Attachment: The Long-Term Bonding Phase.

With the development of the relationships, beyond attraction, attachment mechanisms dominate. This stage is full of neuropeptides like oxytocin and vasopressin, as it is the stage that is full of calmness, security, and emotional connection to the long-term partner [6].

Fig. 1: Phases of Romantic Love