Social behaviour and serotonin:
Some unexpected findings
We all enjoy talking to people who give us energy, who make us feel good. But what about that co-worker who is always negative and criticizing others? And when our mood is low, are we as friendly as we usually are? You can imagine that recurring negative social interactions might over time worsen one’s mood and that of others, and might even result in depression.
I find it intriguing that all types of behaviour, including social behaviour, are regulated by brain chemicals. During my PhD I examined how one of these chemicals, namely serotonin, regulates social behaviour and mood in people at elevated risk for depression.
“I examined how serotonin regulates social behaviour and mood in people at elevated risk for depression.”
People with depression often have difficulties forming and maintaining social relationships. They may show reduced empathy (Schreiter et al., 2013), which might hamper their understanding of others’ feelings during conversations. Moreover, depressed individuals tend to display little prosocial behaviour, e.g., they mimic others’ postures and movements less than non-depressed individuals and may speak in a way that is relatively slow and negative, which limits positive reinforcement from others (Segrin, 2000).
Additionally, depression is often associated with a decreased availability of serotonin, one of the major chemicals in the brain. Serotonin enables the processing of social and emotional information (Albert et al., 2012). Therefore a decrease in the availability of serotonin might have an adverse effect on how we behave and feel during interactions with others. Conversely, an increase in the availability of serotonin might positively affect social interaction.
“The results seem to suggest that social behaviour does not change easily as a result of decreasing serotonin.”
In spite of this supposition, in one of my PhD studies I found that a temporary decrease in brain serotonin (i.e., over a period of 5-7 hours) had little impact on empathy, mimicry, and speech (Hogenelst et al., 2015b; Hogenelst et al., 2016). Participants in the study varied in their familial risk for depression and the results were similar in participants with and without an elevated risk. The results seem to suggest that social behaviour does not change easily as a result of decreasing serotonin. However, the induced change in brain serotonin availability was brief and social behaviour was assessed in the lab, which limits the extent to which the results are relevant for social behaviour as it occurs in everyday life.
In a second study among people with an elevated familial depression risk, rather than inducing an acute decrease, I increased the availability of serotonin over several days (Hogenelst et al., 2015a). Also, this time I examined the effects on social behaviour in everyday life. In a previous study involving highly irritable individuals, who are also at elevated risk for depression, the increase in serotonin led to reduced unfriendliness, more friendliness, and improved mood (aan het Rot et al., 2006). I expected similar results in my study. Indeed, participants’ mood improved. Unexpectedly, however, they became less friendly and more unfriendly when serotonin was increased. These effects on behaviour were only observed during interactions at home, most of which were interactions with partners.
“Participants became less friendly and more unfriendly when serotonin was increased.”
How can this be explained? It is possible that, when serotonin availability was increased, participants were more likely to stand up for themselves. This is in line with the idea that people prone to depression experience little control over their social lives. However, as the results were unexpected, a follow-up study in participants and their partners will provide important insights.
Most medications for depression aim to increase the availability of serotonin. Given the combined findings of the two previous studies (aan het Rot et al., 2006; Hogenelst et al., 2015a), these medications may cause some people to become friendlier whereas others may become more unfriendly. Therefore, another important next question is how these medications affect the social behaviour of depressed people. Such a study may help explain why medications for depression do not always work. Clinicians, patients, and their close others might all profit from this knowledge.
aan het Rot, M., Moskowitz, D. S., Pinard, G., & Young, S. N. (2006). Social behaviour and mood in everyday life: The effects of tryptophan in quarrelsome individuals. Journal of Psychiatry & Neuroscience, 31(4), 253-262.
Albert, P. R., Benkelfat, C., & Descarries, L. (2012). The neurobiology of depression–revisiting the serotonin hypothesis. I. cellular and molecular mechanisms. Philosophical Transactions of the Royal Society of London. Series B, Biological Sciences, 367(1601), 2378-2381.
Hogenelst, K., Schoevers, R. A., & aan het Rot, M. (2015a). The effects of tryptophan on everyday interpersonal encounters and social cognitions in individuals with a family history of depression. International Journal of Neuropsychopharmacology 18(8), pyv012.
Hogenelst, K., Schoevers, R.A., Kema, I.P., Sweep, F.C., aan het Rot, M. (2015b). Empathic accuracy and oxytocin after tryptophan depletion in adults at risk for depression. Psychopharmacology, in press.
Hogenelst, K., Sarampalis, A., Leander, N.P., Müller, B.C.N., Schoevers, R.A., aan het Rot, M. (2016). The effects of acute tryptophan depletion on speech and behavioural mimicry in individuals at familial risk for depression. Journal of Psychopharmacology, in press.
Schreiter, S., Pijnenborg, G. H., & aan het Rot, M. (2013). Empathy in adults with clinical or sub-clinical depressive symptoms. Journal of Affective Disorders, 150(1), 1-16.
Segrin, C. (2000). Social skills deficits associated with depression. Clinical Psychology Review, 20(3), 379-403.
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