Postural reorientation does not cause the locomotor after-effect following rotary locomotion

Abstract

After a period of stepping on a rotating platform, blindfolded subjects demonstrate a tendency to unconsciously turn when stepping in place, an after-effect known as podokinetic after-rotation (PKAR). Recent studies have also reported a change in postural orientation following the adaptive period and have suggested that this is causally related to PKAR. Here, we assess changes in trunk orientation following platform adaptation and determine their relationship to PKAR. Specifically, we determine whether a reorganized standing posture causes PKAR. Ten subjects stepped on a platform rotating at 60deg/s for 10 min, with a cadence of 100 steps/min. Following adaptation, a significant PKAR response was seen, with a mean yaw rotation velocity of 6.0 ± 2.2deg/s. In addition to this dynamic after-effect, there was a significant twist of the trunk with respect to the feet when standing still (6.9 ± 4.5deg; mean ± SD), confirming the presence of a postural reorientation after-effect. However, the magnitudes of the two after-effects did not correlate (r = 0.06, p = 0.87). Furthermore, in a second experiment, a prolonged passive twist of the trunk was used to induce postural reorientation. However, in this case, PKAR was not induced. These results demonstrate that PKAR is not an automatic consequence of reorganized standing posture.