Age-Related Changes in the Plasticity of Neural Networks Assessed by Transcranial Magnetic Stimulation With Electromyography: A Systematic Review and Meta-Analysis.

Zhonghua Yang,Mindong Xu,Yitong Li,Xiaorong Tang,Lin Wang,Peidong Huang,Liming Lu,Nenggui Xu,Juanchao Lan,Wei Yi

doi:10.3389/fncel.2019.00469

Abstract

Objective: The excitability of cerebral cortical cells, neural pathway, and neural networks, as well as their plasticity, are key to our exploration of age-related changes in brain structure and function. The combination of transcranial magnetic stimulation (TMS) with electromyography (EMG) can be applied to the primary motor cortex; it activates the underlying neural group and passes through the corticospinal pathway, which can be quantified using EMG. This meta-analysis aimed to analyze changes in cortical excitability and plasticity in healthy elderly individuals vs. young individuals through TMS-EMG.Methods: The Cochrane Library, Medline, and EMBASE databases were searched to identify eligible trials published from database inception to June 3, 2019. The Cochrane Risk of Bias Tool and improved Jadad scale were used to assess the methodological quality. A meta-analysis of the comparative effects was conducted using the Review Manager 5.3 software and Stata 14.0 software.Results: The pooled results revealed that the resting motor threshold values in the elderly group were markedly higher than those reported in the young group (mean difference [MD]: −2.35; 95% confidence interval [CI]: −3.69 to −1.02]; p < (0.00001). The motor evoked potential amplitude significantly reduced in the elderly group vs. the young group (MD: 0.18; 95% CI: 0.09–0.27; p < 0.0001). Moreover, there was significantly longer motor evoked potential latency in the elderly group (MD: −1.07; 95% CI: −1.77 to −0.37]; p =(0.003). There was no significant difference observed in the active motor threshold between the elderly and young groups (MD: −1.52; 95% CI: −3.47 to −0.42]; p =(0.13). Meanwhile, only two studies reported the absence of adverse events.Conclusion: We found that the excitability of the cerebral cortex declined in elderly individuals vs. young individuals. The findings of the present analysis should be considered with caution owing to the methodological limitations in the included trials. Additional high-quality studies are warranted to validate our findings.

Highlights

As the birth rate decreases and life expectancy increases, the aging problem of the global population becomes more prominent (Tatti et al, 2016)
Consistent with the findings of the present meta-analysis, these results indicate that the function and ability of the M1 cortical region in older individuals decrease with age
We only found limited information related to safety owing to poor reporting of adverse events

Summary

Introduction

As the birth rate decreases and life expectancy increases, the aging problem of the global population becomes more prominent (Tatti et al, 2016). One of the most striking features of human motor behavior is the ability to respond rapidly and appropriately to environmental changes. The decline in cognitive and motor abilities is associated with advancing age (Hunter et al, 2001). This agerelated decline is a precursor of various diseases. An enhanced understanding of the impact of aging on cortical functioning may provide us more insight into understanding of age-related diseases (Seidler et al, 2010)

Methods

Results

Conclusion