Changes in immobility responses in rat pups with maternal stimuli.

Presentation of maternal stimuli to an isolated rat pup results in what has been called "comfort" responses, as indicated by both behavioral and physiological quieting. This experiment investigated the role of passive maternal stimuli on tonic immobility and dorsal immobility in 9- and 16-day-old rat pups. Although these stimuli appeared ineffective in inducing tonic immobility, presentation of the mother did produce an increase in duration of dorsal immobility in 16-day-old pups. This increase in the dorsal immobility response may reduce struggling in the presence of the mother and thereby aid the mother in transporting the infant back to the nest.