Temporal Organizaton in Fetal and Newborn Movement

Abstract

The spontaneous motor activity of the human fetus and newborn infant occurs in cycles of 1 to 4 minutes. The cyclicity emerges in the first half of gestation and remains stable from midgestation through birth. Its postnatal fate is unknown. Animal and human data are consistent with a multisource model, although the cyclicity may arise from interactions among distributed elements with no localized sources of oscillation.

Time-lapse movies have shown that newborn motor activity comes in waves with a period of 1–4 minutes (Robertson, 1982). The cyclicity, however, is not perfectly rhythmic, and the waves of activity may or may not be superimposed on a background of motor silence (Robertson, 1989a). Why do babies do this?

Intrinsic fluctuations are extremely common in living systems, and their adaptive or other significance has been the subject of much speculation and some empirical study (Rapp, 1987). Human cyclic motility (CM) may play a role in early neuromuscular development, and probably regulates interactions with the physical and social environment (Robertson, 1989a). But the general question “why” entails a number of specific questions, in addition to those concerned with utility or consequences (Tinbergen, 1963). In the case of the spontaneous motor activity of the human newborn, specific questions about the development and mechanism of CM must be addressed.

First, we must understand the developmental history and fate of these intrinsic temporal patterns in spontaneous activity. Does the cyclicity in spontaneous movement appear de novo at birth, or does it also characterize the motor activity of the fetus, before birth? If so, what is the course of its prenatal development? Does CM disappear or change substantially during the first few months after birth when other aspects of neurobehavioral organization appear to undergo widespread transitions (Prechtl, 1984)?

Second, we must discover what is responsible for these temporal patterns in fetal and newborn motor activity. What is the neural substrate of CM? Where is the source of the cyclicity? Is there more than one source, or perhaps no sources at all? How should we model the mechanism responsible for the sustained but irregular fluctuations in spontaneous activity?

In this workshop I will focus on the development and mechanism of cyclic motility in the human infant. I will summarize the state of our knowledge in these areas, including the experimental methods that have been used, indicate the gaps in our knowledge, and suggest which empirical and theoretical directions might have the most payoff in the near future.