The Functions of Serotonin and Emotional Stability
Serotonin, chemically 5-hydroxytryptamine or 5-HT, is a neurotransmitter synthesized in the raphe nuclei of the brainstem and projected widely across the whole brain, including the cerebral cortex, the limbic system, and the hypothalamus. Its principal function is the stabilization of emotion: it is involved in restraining anxiety, depression, and aggression, in impulse control, and in the regulation of the sleep-wake rhythm. Reduced function in the serotonin system is associated with depression and anxiety disorders, and selective serotonin reuptake inhibitors, known as SSRIs, are used in treating them. As for the link with personality psychology, activity in the serotonin system has been shown to relate to neuroticism in the Big Five, negatively, and to agreeableness, positively. Polymorphism in the serotonin transporter gene, 5-HTTLPR, is associated with individual differences in sensitivity to stress, and there is a finding that people carrying the short allele are more likely to develop depression in response to stressful life events, although the replicability of this result remains a matter of debate.
Serotonin and Romantic Love
An Italian research team led by Donatella Marazziti reported in 1999 that in people in the early stage of romantic love, within the first six months, the density of platelet serotonin transporters had fallen to a level comparable to that seen in patients with obsessive-compulsive disorder (OCD). The finding suggests that the intrusive thinking characteristic of early love, the inability to stop thinking about the other person, rests on a neurochemical basis similar to that of obsessive thought in OCD. The drop in serotonin promotes the fixation of thought on one particular object, and out of that comes the early-love state in which the other person will not leave one's head. What is striking is that this reduction is reported to return towards normal levels as the relationship continues. The heightened state of early love appears, biologically as well, to be a temporary condition rather than a permanent one. The recovery of serotonin coincides with the period in which a relationship shifts from passionate love toward companionate love, and it occurs in parallel with the decay of dopamine and the increase of oxytocin.
Serotonin and the Quality of Long-Term Relationships
In long-term relationships the serotonin system contributes to relationship quality by way of emotional stability. People whose serotonin system functions well do not overreact to everyday stress and conflict, and they are less prone to falling into emotional flooding. This functions as a protective factor against the flooding Gottman describes. Because serotonin is also involved in impulse control, it restrains explosions of anger and impulsive destructive behavior such as verbal abuse or throwing things. Where the serotonin systems of both partners function well, a calm and stable relationship is easier to maintain. Where one partner's serotonin function is low, something that may be associated with high neuroticism, the resulting swings of emotion place stress on the relationship. From a practical standpoint, sharing the habits that promote serotonin release, meaning regular exercise, sufficient sleep, exposure to sunlight, and meals containing tryptophan, contributes to a couple's emotional stability. The sheer force of a partner's reaction during a quarrel is easily read as a lack of consideration, yet it is not unusual for factors on the side of daily life, such as lack of sleep or exhaustion, to be riding on top of it. Working out when each of you is most easily rattled, and settling on simple arrangements for those periods, not raising heavy topics, resting before talking things through, is more realistic than trying to change a personality.