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

Abstract

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.

An intrinsic source of behavioral regulation that influences discrete responses to cues important for the initiation of suckling.

“…However, in the studies of the late-gestation fetal rat (MacLennan et al, 1998;Reilly et al, 1997), level and variability showed different relationships to oral grasp responses. Differences may be expected because the time scale analyzed in the fetus, 30 s, was much longer than the time scale analyzed in the present study, 5 s before and after oral grasp responses.…”

“…This suggests that cyclicity in motor activity is a robust feature of the temporal organization in motor activity, and, therefore, it may affect the newborn pup's interactions with its environment (e.g., the expression of suckling behavior at the maternal nipple). Demonstration of cyclic temporal organization in the newborn rat and previous demonstration of such activity in the fetal rat (Reilly et al, 1997;Smotherman et al, 1988) indicate continuity in this feature of motor organization across the transition from prenatal to postnatal life. This is further evidence of the robustness of the cyclic pattern.…”

“…The movement data were rectified and integrated to create movement-time series of 1 or 30 Hz depending on the analysis. These techniques have been used reliably in previous studies (MacLennan et al, 1998;Reilly et al, 1997).…”

“…The oral responses of late-gestation fetal rats to suckling stimuli occur on a background of spontaneous motor activity that fluctuates on a time scale of approximately 1 min (Reilly et al, 1997;Smotherman, Robinson, & Robertson, 1988). These fluctuations, known as cyclic motor activity, are persistent and irregular oscillations in general body activity.…”

“…Not only do these fetal responses highlight that the origins of appetitive behaviors of the neonate begin in utero, but they also raise new questions about postnatal behavior. In the present study, we investigate the relationship between neonatal rats' responsiveness to sucking stimuli and spontaneous motor activity that was recently described in the late-gestation fetal rat (Reilly, Robertson, MacLennan, & Smotherman, 1997).…”