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Experimental Brain Research

, 174:256 | Cite as

Dynamical structure of center-of-pressure trajectories in patients recovering from stroke

  • M. RoerdinkEmail author
  • M. De Haart
  • A. Daffertshofer
  • S. F. Donker
  • A. C. H. Geurts
  • P. J. Beek
Research Article

Abstract

In a recent study, De Haart et al. (Arch Phys Med Rehabil 85:886–895, 2004) investigated the recovery of balance in stroke patients using traditional analyses of center-of-pressure (COP) trajectories to assess the effects of health status, rehabilitation, and task conditions like standing with eyes open or closed and standing while performing a cognitive dual task. To unravel the underlying control processes, we reanalyzed these data in terms of stochastic dynamics using more advanced analyses. Dimensionality, local stability, regularity, and scaling behavior of COP trajectories were determined and compared with shuffled and phase-randomized surrogate data. The presence of long-range correlations discarded the possibility that the COP trajectories were purely random. Compared to the healthy controls, the COP trajectories of the stroke patients were characterized by increased dimensionality and instability, but greater regularity in the frontal plane. These findings were taken to imply that the stroke patients actively (i.e., cognitively) coped with the stroke-induced impairment of posture, as reflected in the increased regularity and decreased local stability, by recruiting additional control processes (i.e., more degrees of freedom) and/or by tightening the present control structure while releasing non-essential degrees of freedom from postural control. In the course of rehabilitation, dimensionality stayed fairly constant, whereas local stability increased and regularity decreased. The progressively less regular COP trajectories were interpreted to indicate a reduction of cognitive involvement in postural control as recovery from stroke progressed. Consistent with this interpretation, the dual task condition resulted in less regular COP trajectories of greater dimensionality, reflecting a task-related decrease of active, cognitive contributions to postural control. In comparison with conventional posturography, our results show a clear surplus value of dynamical measures in studying postural control.

Keywords

Motor control Posture Non-linear dynamics Stroke Rehabilitation 

Notes

Acknowledgments

This research was conducted while the first author was working on a grant of the Netherlands Organization for Health Research and Development (ZonMw grant 1435.0004).

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Copyright information

© Springer-Verlag 2006

Authors and Affiliations

  • M. Roerdink
    • 1
    Email author
  • M. De Haart
    • 2
    • 3
  • A. Daffertshofer
    • 1
  • S. F. Donker
    • 1
    • 4
  • A. C. H. Geurts
    • 1
    • 3
    • 5
  • P. J. Beek
    • 1
  1. 1.Faculty of Human Movement Sciences, Institute for Fundamental and Clinical Human Movement SciencesVrije UniversiteitAmsterdamThe Netherlands
  2. 2.Department of Rehabilitation, Amsterdam Medical CentreUniversity of AmsterdamAmsterdamThe Netherlands
  3. 3.Department of Research, Development, and EducationSt. MaartenskliniekNijmegenThe Netherlands
  4. 4.Department of OtorhinolaryngologyVrije Universiteit Medical CentreAmsterdamThe Netherlands
  5. 5.Department of Rehabilitation MedicineUniversity Medical CentreNijmegenThe Netherlands

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