Podokinetic stimulation causes shifts in perception of straight ahead

Abstract

Podokinetic after-rotation (PKAR) is a phenomenon in which subjects inadvertently rotate when instructed to step in place after a period of walking on a rotating treadmill. PKAR has been shown to transfer between different forms of locomotion, but has not been tested in a non-locomotor task. We conducted two experiments to assess effects of PKAR on perception of subjective straight ahead and on quiet standing posture. Twenty-one healthy young right-handed subjects pointed to what they perceived as their subjective straight ahead with a laser pointer while they were recorded by a motion capture system both before and after a training period on the rotating treadmill. Subjects performed the pointing task while standing, sitting on a chair without a back, and a chair with a back. After the training period, subjects demonstrated a significant shift in subjective straight ahead, pointing an average of 29.1 ± 10.6 degrees off of center. The effect was direction-specific, depending on whether subjects had trained in the clockwise or counter-clockwise direction. Postures that limited subjects’ ability to rotate the body in space resulted in reduction, but not elimination, of the effect. The effect was present in quiet standing and even in sitting postures where locomotion was not possible. The robust transfer of PKAR to non-locomotor tasks, and across locomotor forms as demonstrated previously, is in contrast to split-belt adaptations that show limited transfer. We propose that, unlike split-belt adaptations, podokinetic adaptations are mediated at supraspinal, spatial orientation areas that influences spinal-level circuits for locomotion.

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

“…They stood with a fixed rotation of the trunk over the feet by 6.9°, also in a direction opposite to platform rotation. This is consistent with the results of Scott et al (2011) who reported trunk rotation of 8.4°following a 15-min adaptive period. Scott et al (2011) concluded from their findings that postural reorientation reflects transfer of PKAR to a nonlocomotor task.…”

“…This is consistent with the results of Scott et al (2011) who reported trunk rotation of 8.4°following a 15-min adaptive period. Scott et al (2011) concluded from their findings that postural reorientation reflects transfer of PKAR to a nonlocomotor task. Similarly, Hollands et al (2007) suggested that the postural reorganization and PKAR are causally related.…”

“…An adaptive period of rotary locomotion also results in a reorganized standing posture, consisting of a fixed rotation of the trunk over the feet in the same direction as PKAR (Hollands et al 2007;Scott et al 2011). Both Hollands et al and Scott et al have suggested that PKAR is causally related to this postural reorientation.…”

Multiple Time Courses of Vestibular Set-Point Adaptation Revealed by Sustained Magnetic Field Stimulation of the Labyrinth

“…The afterresponse suggests two adaptation processes with time constants of 15 s and 300 s, and even longer periods of stimulation suggest a third on the order of hour(s) [44]. Since our VOR adaptation timescales are close to those for podokinetic adaptation [45], one can speculate the vestibular and podokinetic systems share similar central adaptation operators within a central balance network that incorporates multiple sensory signals [4, 46, 47]. …”

Stepping in Place While Voluntarily Turning Around Produces a Long-Lasting Posteffect Consisting in Inadvertent Turning While Stepping Eyes Closed

“…Of note, during the Kohnstamm movement there is widespread activation of the cerebral cortex [47], and during the PKAR subjects show a direction-specific deviation of the subjective straight-ahead [48]. Therefore, the cerebral cortex, most likely the posterior parietal cortex, must be involved in the body orientation occurring during PKAR and vPKAR.…”