Moderate cardiac vagal tone is associated with more cooperation in children.

Childhood is a crucial period for prosocial development, including cooperative behaviors. Recent studies have shown a quadratic relation (inverted U-shape curve) between cardiac vagal tone (CVT) and various prosocial emotions and behaviors in children, but data are lacking on cooperative behaviors. In a sample of 111 school-aged children (M = 7.77; SD = 1.24, range: 6-11), we tested the association between the root mean square of successive differences in interbeat intervals (RMSSD) at rest, and cooperative behavior in a task designed to be comparable to a stag hunt game. We found evidence for an association between RMSSD and cooperation that follows an inverted U-shape. In addition, older children were more likely to cooperate than younger children. Lastly, we found an interaction between RMSSD and age such that the association between RMSSD and cooperation behavior was present for younger but not older children. In addition, we proposed an extension of the Johnson-Neyman test to assess the significant region of interaction between age and the linear and quadratic RMSSD. These results add to a growing literature suggesting that moderate RMSSD is associated with greater prosocial behavior and provide novel evidence that this association extends to children's cooperation.