Scaling oscillatory platform frequency reveals recurrence of intermittent postural attractor states

Aviroop Dutt-Mazumder,Karl M Newell,Troy J Rand,Mukul Mukherjee

doi:10.1038/s41598-018-29844-2

Abstract

The study of postural control has been dominated by experiments on the maintenance of quiet upright standing balance on flat stationary support surfaces that reveal only limited modes of potential configurations of balance stability/instability. Here we examine the self-organization properties of postural coordination as revealed in a dynamic balance task with a moving platform. We scaled a control parameter (platform frequency) to investigate the evolving nature of the coupled oscillator dynamics between center of mass (CoM) and platform. Recurrent map measures were used to reveal whether episodic postural control strategies exist that can be scaled by systematically changing the magnitude of platform motion. The findings showed that at higher platform frequencies (1.2 Hz), the CoM-Platform coupling was less deterministic than lower platform frequencies and evolved to intermittent postural control strategies that oscillated between periodic-chaotic transitions to maintain upright postural balance. Collectively, the recurrence map measures indicated that quasi-static postural attractor states were progressively emerging to the changing task constraints of platform frequency in the maintenance of postural stability. It appears that several dynamic modes of intermittent coupling in postural control can interchangeably co-exist and are expressed as a function of the control parameter of platform frequency.

Highlights

Postural control encompasses non-linear interactions of subsystems involving sensory and motor processes that collectively organize to maintain postural balance[1,2]
An open question in motor control and, that we investigate here, is whether the scaling of a control parameter would reveal any intermittent postural control strategies
Postural balance task[17,18], supra-postural bimanual task[19] and continuous oscillatory platform motion[20,21,22]. In both anterior-posterior[23] and medio-lateral[24] moving platform postural tasks, CoM motion to that of platform motion remained in-phase or transitioned to anti-phase as a function of the platform frequency. These results have provided preliminary evidence that the relative coupling of center of mass (CoM - an emergent macroscopic property) with respect to the oscillatory platform motion could be considered as a collective variable for upright postural stance task[23,25]

Summary

Introduction

Postural control encompasses non-linear interactions of subsystems involving sensory and motor processes that collectively organize to maintain postural balance[1,2]. An open question in motor control and, that we investigate here, is whether the scaling of a control parameter (externally triggered perturbation of oscillating platform frequency) would reveal any intermittent postural control strategies (quasi-static postural attractor states). In both anterior-posterior[23] and medio-lateral[24] moving platform postural tasks, CoM motion to that of platform motion remained in-phase or transitioned to anti-phase as a function of the platform frequency These results have provided preliminary evidence that the relative coupling of center of mass (CoM - an emergent macroscopic property) with respect to the oscillatory platform motion could be considered as a collective variable for upright postural stance task[23,25]. Progressive scaling of platform frequency would provide us a closer insight into the postulated intermittent coupling of CoM-platform oscillators, their nature of emerging attractor states, and the duration of trapped attractor states

Methods

Results

Discussion

Conclusion