Elsevier

Gait & Posture

Volume 39, Issue 1, January 2014, Pages 420-423
Gait & Posture

Decreased dynamical complexity during quiet stance in children with Autism Spectrum Disorders

https://doi.org/10.1016/j.gaitpost.2013.08.016Get rights and content

Abstract

Background

Postural control deficits in individuals with Autism Spectrum Disorders (ASD) are widely acknowledged; however, the underlying biomechanical features of these deficits remain unknown. Nonlinear analyses provide insight into the nature of how movement is controlled and have the potential to provide new insight into the postural control abnormalities associated with ASD. The purpose of this study was to further investigate postural control deficits in children with ASD through linear and nonlinear analyses of center of pressure (COP) data.

Methods

We evaluated COP data during quiet standing for 16 children with ASD and 17 age-matched typically developing (TD) children. The magnitude of COP fluctuations (COP ranges, velocity, and sway area) and complexity of postural control dynamics, quantified by multiscale entropy (MSE), were compared across groups.

Results

Children with ASD displayed larger fluctuations in their COP data, observed in COP ranges (95.5% mediolaterally and 46.9% anteroposteriorly, p < 0.05 respectively) and COP sway area (885%, p < 0.05). Children with ASD also displayed less complexity in their COP data, observed in the MSE complexity index (CI) (32.4% mediolaterally and 35.7% anteroposteriorly, p < 0.05 respectively).

Conclusions

The present study successfully revealed that children with ASD have more repetitive patterns in their COP data, indicating a less complex control of posture, on multiple time scales, during quiet stance. These findings suggest a more regular or restricted control of posture and may be an initial step in linking postural instability to stereotypic behavior and the neurobiology of ASD.

Introduction

The ability to maintain posture is at the core of typical motor development in humans. Children diagnosed with Autism Spectrum Disorders (ASD) exhibit an impaired ability to control quiet stance when compared to typically developing children (TD) [1], [2], [3]. Abnormal movements, including deficiencies in postural control, appear to be pervasive across the spectrum of autism disorders [4], [5], [6]. While the presence of these impairments has been grossly described in the literature, very little has been done to investigate underlying features of postural performance beyond spatial evaluation of postural sway. Therefore, further elucidation of the nature of these disturbances may provide further insight into possible mechanisms contributing to impaired postural control.

Postural control has been studied extensively in clinical populations (for example; Parkinson's, Stroke, Cerebral Palsy, and ASD) and using a variety of experimental tasks (for example; sitting, standing, sit-to-stand, and gait initiation). Linear analytical techniques have been widely used to describe the gross output of the nervous system's response to maintaining balance (center of pressure (COP) sway area, COP path length, etc). More recently, nonlinear analytical techniques (i.e., approximate entropy, Lyupanov exponents, and multiscale entropy (MSE)) have been used to complement traditional measures in order to provide further insight into the structural nature or complexity of how movement is controlled [7]. Restrictive and repetitive behaviors are distinctive characteristics of children with ASD. This behavioral rigidity has been linked to potential deficits in frontal cortical and striatal function; circuitry which may also influence postural control [8]. Thus, this centrally mediated rigidity may carry over and manifest as less complex control of the COP time series during postural control tasks.

The purpose of this study was to further investigate the nature of the postural control deficits previously reported in children with ASD, through linear and nonlinear analysis of standing posturography data. We hypothesized that children with ASD would have more periodic COP patterns during quiet stance than TD children and thus have smaller entropy values observed on multiple time scales as indicated by lower MSE indices (Complexity Index in the mediolateral direction (CI-X) and in the anteroposterior direction (CI-Y))

Section snippets

Participants

Sixteen children diagnosed with ASD (age: 5.5 ± 1.1 years, height: 1.2 ± 0.1 m, mass: 24.0 ± 6.0 kg, Leiter-R Brief IQ: 81.6 ± 23.4) were recruited from the University's Child & Adolescent Psychiatry Clinic. Seventeen age-matched typically developing (TD) children (age: 6.2 ± 1.2 years, height: 1.2 ± 0.1 m, mass: 20.8 ± 3.0 kg, Leiter-R Brief IQ: 115.5 ± 13.5) were recruited from the community and served as controls. Clinical diagnoses of ASD were initially determined by a licensed professional (psychologist or

Results

Children with ASD exhibited significantly smaller CI values when compared to TD children. The CI values were 32.4% smaller in the mediolateral direction (CI-X) and 35.7% smaller in the anteroposterior direction (CI-Y). Entropy values associated with each time scale analyzed are presented in MSE curves for both the mediolateral and anteroposterior directions (Fig. 1, Fig. 2). As expected, COP ranges were significantly larger in children with ASD when compared to TD children (95.5% larger and

Discussion

Appropriate postural control is a necessary foundation for individuals to acquire skills inherent to functional independence. Herein, we applied nonlinear analyses (MSE) of the COP time series to extract more information about the nature of differences in postural control previously described in the literature between ASD and TD [1], [2], [3], The main finding of this work is that children with ASD exhibit greater postural sway with reduced complexity in their COP time series.

Our hypothesis

Acknowledgments

This study was supported in part by Autism Speaks (# 1964/01-201007-065-00-00-01). The content of this manuscript is solely the responsibility of the authors and does not necessarily represent the official views of Autism Speaks.
Conflict of interest statement

None of the authors have financial or other conflicts of interest in regards to this research.

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