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

Rat fetuses exhibit intrinsic fluctuations ingeneral 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 hat presentation of the AN triggers behavioral reorganization i which the level and variability of overall activity may facilitate expression of well-defined action patterns. A principal aim of the neuroembryological study of behavior has been to examine behavioral patterns that emerge in the embryo and fetus amid continuous nervous system development, organogenesis, and environmental influence (Oppenheim, 1982). Investigations of embryonic and fetal behavior have sought to illuminate the role of activity in neurobehavioral development. Typically, prenatal behavior has been conceptualized asessential to normative development and postnatal behavior, as an ontogenetic adaptation to conditions within the prenatal environment or as an epiphenomenon reflecting central nervous system functioning at a given time in development (Oppenheim, 1981, 1984). As research on behavior during early develop-ment has advanced, it has become obvious that fetal behavior both serves adaptive functions in the prenatal environment and prepares the organism for postnatal lif