By Dr. Yacila Deza-Araujo
(posted 11th May 2021)
Serotonin – a neurotransmitter which helps regulate emotional well-being and other important physiological functions – can decrease in the brain as we age. Although this statement is still a matter of debate [1, 2], we know that several studies have observed less availability of this neurotransmitter in specific parts of the ageing brain .
Similarly, clinical studies have demonstrated that some symptoms of depression in older adults become less pronounced after treatments that boost brain serotonin availability. Therefore, the popular belief that serotonin is the ’happiness hormone’ is not far from the truth.
Our study  was led by the Silver Santé Study’s Emotion Work Package in close relation with the blood markers workgroup (namely Géraldine Poisnel and Anne Chocat), using data from the Age-Well trial. In this context, our study shows that the blood levels of serotonin may be crucial to regulate the activity of some brain areas associated with emotional responses.
Specifically, we observed that participants with lower levels of serotonin in their blood have more brain activity in certain parts of the brain when viewing videos depicting others suffering. These brain regions are well known to be implicated in the processing of salient emotional stimuli (i.e., insula), in the regulation of strong emotions (i.e., dorsal anterior cingulate cortex) and in the expression of sadness (i.e., subgenual cingulate cortex).
This discovery might also give us some idea of the level of empathy that the participants experienced when observing these videos. Interestingly, however, we did not see any relation between blood serotonin and behavioural measures of emotions and prosocial behaviour -“voluntary actions that are intended to help or benefit another individual or group of individuals” . Before our study, the relationship between serotonin in the blood and emotional brain activity had only been investigated in patients with depression and younger people. Our study investigated for the first time, this relationship in older adults.
We are confident that our results, as well as other findings from the Silver Santé Study, will contribute to increasing the understanding of determinant factors that might improve the mental well-being of older adults and therefore decrease the risk of mood disorders and dementia.
1. Rosa-Neto, P., et al., Brain regional alpha-[11C]methyl-L-tryptophan trapping, used as an index of 5-HT synthesis, in healthy adults: absence of an age effect. Eur J Nucl Med Mol Imaging, 2007. 34(8): p. 1254-64.
2. Karrer, T.M., et al., Reduced serotonin receptors and transporters in normal aging adults: a meta-analysis of PET and SPECT imaging studies. Neurobiology of Aging, 2019. 80: p. 1-10.
3. Deza-Araujo, Y.I., et al., Whole blood serotonin levels in healthy elderly are negatively associated with the functional activity of emotion-related brain regions. Biol Psychol, 2021. 160: p. 108051.
4. Eisenberg, N and Mussen, P H. The Roots of Prosocial Behavior in Children. Cambridge: Cambridge University Press, 1989: p 3.