The neural signaling molecule oxytocin, which influences how animals interact, is sometimes portrayed as a “love hormone,” but it’s not that simple. This shouldn’t be surprising given that it’s an evolutionarily ancient neuromodulator, one that affects a wide variety of emotions and social interactions – these are hardly simple things.
A more current, nuanced view of its effects holds that, rather than simply enhancing bonding, love, and trust, it serves to enhance people’s social consciousness. This can have a downside – like alcohol, it can amplify the feelings one already has for someone else, whether they are positive or negative. It can also strengthen bonds only within a clique, to the exclusion of everyone at the other lunch tables.
While it’s clear that oxytocin certainly has powerful effects on emotion and social cognition, it’s less clear how this happens. Individuals express different levels of oxytocin, but these different levels have never been conclusively linked to social skills or disabilities – and it’s not for lack of trying.
Like all hormones, oxytocin cannot work alone; it exerts its effects by binding to a receptor. As with oxytocin itself, individuals express different levels of the oxytocin receptor. The oxytocin receptor gene is subject to methylation, an epigenetic modification that chemically modifies the gene’s DNA, which regulates how much of the receptor is made. More methylation means fewer receptors are made, so less oxytocin signaling reaches the cells.
More methylation at the receptor gene has been found in people with autism, anorexia, and those with “hard emotional traits,” suggesting it may act as a biomarker for these behavioral tendencies. Researchers at UVA wondered if different levels of methylation might be related to differences in neural activity during a particular social perception task: emotional facial processing. See, they were.
The researchers measured the methylation levels of ninety-eight white adults, put them in an fMRI scanner and showed them pictures of angry or frightened faces. When looking at the faces, study participants with higher levels of methylation—thus less oxytocin activity—had increased blood flow to the left hemisphere of their amygdalas. That brain region is known to respond to negative stimuli, such as angry faces.
Other brain areas important for face and social perception and emotion processing were also hyperactivated in these people, but functional connectivity between the amygdala and these areas was reduced. The researchers suggest that oxytocin is involved in attenuating the fear response generated by the amygdala, noting: “These results provide compelling evidence suggesting that social perceptual and emotional processes thought to involve the endogenous oxytocin system can be controlled by epigenetic processes.”
It has been suggested that oxytocin may promote social behavior not only by increasing social sensitivity, but also by alleviating social anxiety. These results support the latter idea. People with lower levels of methylation on the oxytocin receptor gene have more oxytocin signaling and so they don’t get as excited when they see angry or frightened faces, as evidenced by the relatively slow response of their amygdalas. These people also show increased coupling between their amygdalas and other brain regions, which can make them desensitized to the negative and threatening stimuli represented by the faces.
The authors point out that there is a clear “lack of behavioral evidence to reveal how these epigenetic and neural markers influence the overt social phenotype.” In other words, beyond the signals in an MRI scan, it’s not clear what the significance of these changes is.
So this study doesn’t provide an excuse for anyone to go out and sniff oxytocin (yes, unfortunately it’s available as a nasal spray). But it does show that epigenetic mechanisms can influence very complex interpersonal behavior. And since these mechanisms are both inherited and can be altered by the environment, these results could have far-reaching and fascinating implications.
PNAS2014. DOI: 10.1073/pnas.1422096112 (About DOIs).