How does neurochemistry affect attachment styles in humans? The role of oxytocin and the endogenous opioid system in sociotropy and autonomy - a systematic review.

Oxytocin was hypothesised to play a critical role in forming and maintaining secure attachments, shown to confer resilience against affective disorders. The endogenous opioid system has also emerged as a key player in attachment dynamics. In this pre-registered systematic review, we investigated whether individual differences in the functioning of these neurochemical systems are related to attachment styles, following PRISMA guidelines. As predicted, individuals with higher oxytocin function exhibited more secure attachment styles (p=.006, n=12 studies) and less insecure attachment styles (p=.021, n=16 studies). Contrary to our hypothesis, we found no association of endogenous opioid function with insecure (p=0.549, n=11 studies) or secure attachment styles (p=.065, n=11 studies). The lack of association between endogenous mu-opioid function and attachment styles remains inconclusive due to inconsistencies in the neurochemical measurements and lack of eligible studies. Therefore, further investigations into the role of the endogenous opioid system in attachment styles are needed. Our findings corroborate the hypothesis that individual differences in oxytocin function relate to differences in attachment styles.