VARIATION IN MOTOR-ACTIVITY ON DIFFERENT TIME SCALES AND RESPONSIVENESS TO ORAL-STIMULATION IN THE RAT FETUS

The near-term rat fetus exhibits brief or al grasp responses to discre te presentations of an artificial nipple. In the present experiment, a n artificial nipple was presented to individual fetal subjects 10 time s. Five of the presentations were timed to occur when spontaneous feta l motor activity was law and five while activity was high, as determin ed by the baseline activity for the individual fetus. The likelihood o f responding to the artificial nipple was increased when the fetus was relatively inactive at the moment of stimulus presentation. Furthermo re, stimulus presentations that resulted in oral grasping of the artif icial nipple were associated with greater point-to-point variability ( 2-s intervals) in motor activity during the 30-s period preceding the presentation of the artificial nipple. This pattern of results indicat es that the recent history of general motor activity as well as the le vel of activity at the instant of stimulus presentation may contribute to variation in responding to biologically relevant stimuli early in development. (C) 1998 John Wiley & Sons, Inc.