空中立ち直り反射における下行性の姿勢制御

抄録

Postural control may be performed on the basis of certain reference frames. Two kinds of reference are usually adopted, one based on the support surface and the other, head-centered reference. In usual cases, these two may be flexibly and dynamically integrated. To understand such integration, we investigated the air-righting movement in rats. Because of lack of a support surface during falling, air-righting may be evoked by a control system based on the head-centered reference.
Air-righting movements were evoked in male Wistar rats. In some rats the cerebellar vermis was ablated in various degrees (decerebellate animals). Righting movements and muscle activities were analyzed. Righting movements were recorded on a videocassette recorder (30 frames/sec). Video pictures were captured into a computer frame by frame. Muscle activities were recorded from axial muscles (m. longissimus thoracis) on both sides.
Air-righting consisted of three kinds of movement in rats with intact brain: head and upper body rotation against the lower body, lower body rotation against the upper body, and four limbs extension in the prone posture. These movements occurred sequentially in the above-mentioned order. After the head and upper body rotations, the head almost righted in space, and the hip maximally twisted. This torsion of the hip was removed by the second movement, the lower body rotation. After the second movement, the whole body righted and the animal could take a prone posture. Then, the third movement, limb extension, occurred.
In decerebellate animals, the same basic movements were induced during air-righting. However, the magnitudes of rotations were different from those of intact rats. Sometimes magnitudes of rotations were so small that air-righting movements were incomplete (undershooting). In other cases, rotations were so large that air-righting was excessive (overshooting). In extreme cases, decerebellate rats rotated their bodies more than twice during a single fall. In both undershooting and overshooting, the removal of axial torsion of the body at the hip seemed to take place; thus, the whole body in such cases inclined along the long axis after the second movement. In such cases, the third movement was not evoked. To elicit the third movement, the animal was assumed to be in the prone position.