Often called the love hormone, oxytocin has shown the ability to enhance social bonding, decrease anxiety and encourage an overall feeling of satisfaction with life. A new study out of Northwestern University, however, finds that this ancient hormone has a dark side, and is capable of strengthening unpleasant memories, fear, and anxiety. This Jeckyll and Hyde behavior results from the fact that oxytocin has a general strengthening effect on social memories, without regard to their polarity.

Although discovered in 1906, study of the emotion-altering effects of oxytocin are still in their infancy. Experiments on humans as well as animal models strongly suggest that oxytocin is associated with pair bonding, social recognition, ethnocentricity (the "in group" effect), increasing trust, decreasing fear, and even improved wound healing. An interesting example of this class of effects can be found in a 2012 study which showed that oxytocin caused men in a monogamous relationship to maintain four to six inches more space between themselves and an attractive woman in a crowd, while having no effect on single men.

Other, less positive properties of oxytocin dosage have also begun to be reported. For example, a study from the University of Haifa found that the emotions of envy and Schadenfreude (pleasure in another's misfortune) were increased by internasal administration of oxytocin. Further research suggests people with borderline personality disorder, whose major symptom is a tendency to withdraw from social interactions, exhibit less trust when treated with oxytocin. This was particularly true in those who were sensitive to rejection. Clearly, oxytocin's effects on people's emotions are not as simple as originally suggested.

This new study from Northwestern University demonstrates that oxytocin is associated with emotional pain. In increasing the strength of social memories, it may be the reason that stressful social situations (bullying, abuse, ridicule, rejection) can easily be brought to mind long after the event. The intensity of such memories can be such that the memory feels almost like living through the original event every time you think of it.

The Northwestern study, carried out by Dunbar Professor Jelena Radulovic's group, found that during a stressful social experience, oxytocin is released and activates a part of the brain that intensifies the memory. Oxytocin also increases the susceptibility to feeling fearful and anxious during stressful events going forward. It seems likely that oxytocin also intensifies positive social memories, but this has not explicitly been examined as yet.

Professor Radulovic's study is the first to link oxytocin to social stress and its ability to increase anxiety and fear in response to future stress. The researchers also discovered the brain region responsible for these effects – the lateral septum – and the pathway or route oxytocin uses in this area to amplify fear and anxiety.

The findings surprised the researchers, who were expecting oxytocin to intensify positive emotions in memory, based on its long association with love and social bonding.

"Oxytocin is usually considered a stress-reducing agent based on decades of research,” said Yomayra Guzman, a doctoral student in Radulovic’s lab. "With this novel animal model, we showed how it enhances fear rather than reducing it and where the molecular changes are occurring in our central nervous system."

Far from a simple "cuddle hormone," oxytocin appears to have the same complex interaction with human health and behavior as most other hormones. While a good deal of progress has been made, there is still work to do when it comes to to unknotting the tangled ball of yarn that is oxytocin's effects.

Source: Northwestern University