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The experiments were performed on 18 albino newborn rats of both sexes. The postnatal development of the air-righting-reaction (ARR) of the rats was tested for 4 different falling heights (30, 40, 50 and 60 cm) with 3 different loading conditions: artificial alteration of the head, thorax and pelvis mass, respectively. The reaction was analyzed in terms of a three-segment model of the rat (three rotatable parts: head-thorax-pelvis with only one degree of freedom between successive segments). Loading of the head resulted in a delayed development of the first phase of the ARR, whereas loading of the trunk or pelvis slowed the second phase of development. In general, it appears that loading of a body segment results in a delayed development of the rotation of that segment during free fall. Furthermore, loading of a caudal region was associated with an earlier rotation of cranial segments. The completion of the ARR maturation process showed no dependency on either the location or the size of the load, suggesting that the postnatal development of the ARR is pre-programmed.

The aim of this study was to describe the ontogenesis of the air-righting reaction (ARR) in rats. The first experiment was performed on 6 newborn albino rats of both sexes and followed the development of the ARR over postnatal days 1-21. The degree of rotation achieved after falling from different heights was quantified according to a rating scheme. It appeared that the air-righting reaction is effected by a spiral movement which spreads in a cranio-caudal direction. The reaction develops between postnatal day 8 and 18. On postnatal day 10 only a few animals are able to turn their heads, this being possible only from a falling height of 60 cm and corresponding to a falling time of 350 ms. A rapid development of the reaction was found between days 10 and 14. The second experiment on 8 rats involved the use of immobilization in order to isolate the mechanisms that trigger the ARR. The immobilization prevented neck-torso rotation, torso-pelvis rotation, and both rotations in different animals. Despite the disruption of important (afferent) feedback systems, the reaction developed within the same age period as in control rats. Thus, the Magnus "chain reflex hypothesis' as basis for the ARR is rejected in favor of a central motor program hypothesis.