Variability in general activity and the expression of complex behavior in the fetal rat (Rattus norvegicus).

Rat fetuses exhibit intrinsic fluctuations in general motor activity and respond to an artificial nipple (AN) with mouthing and oral grasping behavior. The present study examined the relation between the organization of general activity and the expression of these specific responses to an AN on Embryonic Day 21. In Experiment 1, continuous exposure to the AN resulted in nonspecific behavioral activation characterized by an increase in amplitude and high-frequency variability. In Experiment 2, increased amplitude and variability in general activity preceding discrete presentations of the AN resulted in more mouthing and oral grasping responses to the AN. These results suggest that presentation of the AN triggers behavioral reorganization in which the level and variability of overall activity may facilitate expression of well-defined action patterns.