Background:
Attunement, or synchrony, of behavior and physiology has been well documented in family, mother-child, and romantic relationships. This study aimed to determine whether attunement of the hypothalamic-pituitary-adrenal (HPA) axis occurs in women’s close friendships, and the role of a common social style, co-rumination in that attunement. Saliva samples (later assayed for cortisol) were collected from 37 dyads (74 individuals) during a laboratory task in which they were either asked to work together toward a common goal (control task) or discuss interpersonal problems, providing opportunity for co-rumination. Findings suggest that friends demonstrated adrenocortical attunement prior to engaging in either task, and that the level of attunement prior to the task predicted co-rumination and its components for both groups. Co-rumination, in turn, predicted adrenocortical attunement after the task. These findings suggest that bidirectional attunement of HPA activity may serve a bonding function within women’s close friendships. Implications for how these findings fit with the tend-and-befriend hypothesis are discussed.

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