Age-Related Differences in Corticospinal Excitability and Anticipatory Postural Adjustments of the Trunk.

Rebecca S Rowland,Ned Jenkinson,Shin-Yi Chiou

doi:10.3389/fnagi.2021.718784

Rebecca S Rowland, Ned Jenkinson + Show 1 more

Open Access

https://doi.org/10.3389/fnagi.2021.718784

Copy DOI

Abstract

Anticipatory postural adjustments (APAs) are a feedforward mechanism for the maintenance of postural stability and are delayed in old adults. We previously showed in young adults that APAs of the trunk induced by a fast shoulder movement were mediated, at least in part, by a cortical mechanism. However, it remains unclear the relationship between delayed APAs and motor cortical excitability in ageing. Using transcranial magnetic stimulation we examined motor evoked potentials (MEPs) of the erector spinae (ES) muscles in healthy young and old adults prior to a fast shoulder flexion task. A recognition reaction time (RRT) paradigm was used where participants responded to a visual stimulus by flexing their shoulders bilaterally as fast as possible. The activity of bilateral anterior deltoid (AD) and ES muscles was recorded using electromyography (EMG). The onset of AD and ES EMG was measured to represent RRT and APAs, respectively. We found increases in amplitudes of ES MEPs at 40 ms than 50 ms prior to the EMG onset of the AD in both groups. The amplitude of ES MEPs at 40 ms prior to the onset of AD EMG correlated with the onset of ES activity counterbalancing the perturbation induced by the shoulder task in the elderly participants only. Our findings suggest that timing of increasing corticospinal excitability prior to a self-paced perturbation becomes more relevant with ageing in modulating postural control of the trunk.

Highlights

Postural control involves the ability to maintain one’s center of mass (COM) over the base of support in response to perturbation (Hess et al, 2006)
There was a delay in the onset of EMG activity in the erector spinae (ES) with respect to the onset of EMG activity in the anterior deltoid (AD) in the older participants compared with the young participants (Figure 2C)
We found that ES motor evoked potentials (MEPs) at −40 ms correlated with the onset of ES EMG in the elderly cohort, FIGURE 2 | Anticipatory postural adjustments (APAs). (A) Electromyography (EMG) traces recorded from left erector spinae (ES) and right anterior deltoid (AD) of representative old and young participants

Summary

Introduction

Postural control involves the ability to maintain one’s center of mass (COM) over the base of support in response to perturbation (Hess et al, 2006). APAs occur prior to movements and are a feedforward process that counteract an expected perturbation (Alexandrov et al, 2005; Hall et al, 2010). It is considered as a first line of defence for postural stability in anticipation of perturbations and has been observed whilst sitting, standing, or walking (Aruin and Shiratori, 2003). In contrast to the absence of APAs that can be seen in Corticospinal Contribution to Posture Adjustments in Older Adults neurological conditions such as Parkinson’s disease (Bazalgette et al, 1987), it is thought that the APAs in elderly people are delayed, resulting in increased responses of, and reliance upon, CPAs to maintain balance (Kanekar and Aruin, 2014). While it is recognized that APAs of the trunk in response to a perturbation, measured by electromyography (EMG), are delayed in older adults, it remains largely unclear whether age-related changes in the neural control of APAs exist

Objectives

Results

Discussion

Conclusion