Schino, G., Scucchi, S., Maestripieri, D. et al. 1988. Allogrooming as a tension-reduction mechanism: A behavioral approach. American Journal of Primatology 16, 43-50.

Receiving grooming, unlike performing grooming, reduced tension both during the interaction and at other times, as documented by decreased displacement activity rates. ... Although social and hygienic functions of allogrooming are compatible, the role of allogrooming in developing and stabilizing primate social relationships appears to be especially important.