Wikipedia
Co-regulation (or coregulation) is a term used in psychology, defined most broadly as a "continuous unfolding of individual action that is susceptible to being continuously modified by the continuously changing actions of the partner." An important aspect of this idea is that co-regulation cannot be reduced down to the behaviors or experiences of the individuals involved in the interaction. The interaction is a result of each participant repeatedly regulating the behavior of the other. It is a continuous and dynamic process, rather than the exchange of discrete information.
Co-regulation is often applied in the context of emotions. In this sense, the emotions of each individual within a dyad are constantly in flux, depending on the emotions and behaviors of the partner. If emotion co-regulation is in effect, the result will be a decrease in overall emotional distress. A working definition of emotion co-regulation has been offered as “a bidirectional linkage of oscillating emotional channels between partners, which contributes to emotional stability for both partners.” Emotion co-regulation is thoroughly studied in the context of early emotional development, often between infants and caregivers. It has also been studied in adult interpersonal interactions, with an emphasis on close, romantic relationships. One important note regarding co-regulation is that there may be an imbalance within the dyad, such that one member is more actively regulating the behavior of the other.
The following is an example of co-regulation between a mother and her infant, from Emotional development: The organization of emotional life in the early years. This scenario exemplifies a mother maintaining her infant’s engagement via variations in her voice, facial expressions, and body language. She sensitively elicits behaviors from the infant and adds more stimulation when appropriate. Likewise, the infant indicates and maintains the mutual engagement with her own facial expressions, vocalizations, and body language.
“Hello there pumpkin . . . Mommy's comin' to get you. Yes, she is. [Brief pause.] Momma's gonna get you and tickle you. What do you think of that? [Brief pause.] Come on. Come on, you little sweetie. Let me see that smile. Humm? [Pause.] Yeah, that's right . . . thaaaat's right. [The infant exhibits a big smile with bobbing head, and mother responds in kind, then says,] Oh, well now, are you gonna say somethin'? Are ya? [Pause, mother nodding head, widening eyes.] Come on! [Pause.] Come on! [The baby begins cycling movements of the arms and kicking the feet.] Come on. [Drawn out, then longer pause.] Yeah! [as the baby bursts forth with a gurgling sound, the caregiver then laughs and hugs the baby].”