The development of behavior before birth.

Abstract

Study of the fetus in vivo provides a simple system for experimental study of early neurobehavioral development. This review summarizes research on the development of behavior before birth including studies where fetuses are exposed to stimuli that mimic features of the neonatal environment, such as milk and an artificial nipple. These stimuli reliably evoke responses from fetal subjects, including species-typical behavior such as the stretch response and oral grasping of the artificial nipple. Contingent presentations of the nipple and milk can result in classical conditioning, including activation of the endogenous opioid system. Quantitative analysis of fetal motor behavior coupled with the use of ecologically relevant sensory manipulations provide a means for assessing integrated output of the developing nervous system. A general article with the title Development of Behavior Before Birth implies a number of topics that might be discussed. One may anticipate that such an article would provide an historical overview of the field of behavioral embryology or a survey of the diverse approaches used to measure behavior in utero. Recent reviews have appeared that have adequately described historical context (Oppenheim, 1982, 1992) and research methods that currently are permitting study of prenatal behavioral development (Nijhuis, 1992; Smotherman & Robinson, 1988a), so these issues will not be addressed in the present report. Alternatively, one might expect such an article to pose speculative scenarios for prenatal learning or cognition, or to suggest how parents can interact with the fetus within the womb. The subject of prenatal enrichment has received widespread attention in the popular press, but dubious claims by authors and marketeers actually may have impeded empirical investigation of fetal behavioral capacities. Rather than belaboring issues that have been adequately addressed elsewhere, or which do not merit scientific discussion, this article will focus on the findings and implications that have emerged from experimental study of fetal behavior, primarily in nonhuman species. It is our thesis that the mammalian fetus is interesting in its own right because it exhibits a rich and sophisticated behavioral repertoire (Robinson & Smotherman, 1992a; Smotherman & Robinson, 1990), and that study of the mechanisms that regulate behavior in the nonhuman fetus can provide unique insights into the general rules that direct neurobehavioral development and the research methods needed to identify them (Robinson & Smotherman, 1988; Smotherman & Robinson, 1988b, 1994a).