THE INFLUENCE OF MATERNAL PRESENCE ON THE ORIENTING RESPONSE IN PREWEANLING RATS

The orienting response is an unconditioned reaction to novel innocuous stimuli that occurs in many species, including laboratory rats and humans. In infant and adult rats, the orienting response is disrupted by both an unifamiliar environment and a mildly painful electric shock. If this disruption is due to an increase in fear or arousal, then alleviation of that distress should permit normal occurrence of the orienting response. The purpose of the present research was to asses the effects of maternal presence, an established means of alleviating situation- or shock-induced distress, on elicitation of the orienting response in preweanling rats. Four experiments were conducted to assess the effects of maternal presence, in the form of an anesthetized, lactating dam, on elicitation of the orienting response (OR) in 16-day-old preweanling rat pups to a pulsating, 1600-Hz tone following placement in an unfamiliar environment (Experiment 1) and a brief electric shock (Experiment 2), while attached to a nipple (Experiment 3), and while in the presence of either their natural mother or an unfamiliar lactating dam (Experiment 4). Maternal presence did not facilitate elicitation of the OR when it was inhibited either by an unfamiliar environment or by electric shock even though it lowered basal heart rates, indicative of a lowered level of arousal. In those conditions where the orienting response was elicited (e.g., following adaptation to the test cage), maternal presence did not affect either magnitude or rate of habituation (Experiments 1 and 2). The same general results were obtained whether animals were tested with their biological mother or with unknown lactating female (Experiment 4). The only apparent effect of maternal presence on elicitation of the orienting response was that suckling inhibited the behavioral component of this response without affecting the cardiac response (Experiment 3). The results of this study are discussed in terms of (a) the role of stimuli from the home environment on cognitive functioning in the developing animal, and (b) the theoretical mechanisms that may underlie inhibition of the orienting response.