Individuals with Higher Levels of Physical Activity after Stroke Show Comparable Patterns of Myelin to Healthy Older Adults

Higher levels is not a scientific term, the mentors and senior researchers need remedial training in research in general.  Useless.

Individuals with Higher Levels of Physical Activity after Stroke Show Comparable Patterns of Myelin to Healthy Older Adults

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Brian Greeley, PhD, Cristina Rubino, MSc, Ronan Denyer, MSc, ...

First Published May 9, 2022 Research Article Find in PubMed 

https://doi.org/10.1177/15459683221100497

Article information

Abstract

Background

Myelin asymmetry ratios (MARs) relate and contribute to motor impairment and function after stroke. Physical activity (PA) may induce myelin plasticity, potentially mitigating hemispheric myelin asymmetries that can occur after a stroke.

Objective

The aim of this study was to determine whether individuals with higher levels of PA showed lower MAR compared to individuals with lower levels of PA.

Methods

Myelin water fraction was obtained from 5 bilateral motor regions in 22 individuals with chronic stroke and 26 healthy older adults. Activity levels were quantified with wrist accelerometers worn for a period of 72 hours (3 days). Higher and lower PA levels were defined by a cluster analysis within each group.

Results

MAR was similar regardless of PA level within the older adult group. Compared to the higher PA stroke group, lower PA stroke participants displayed greater MAR. There was no difference in MAR between the stroke and older adult higher PA groups. Within the lower PA groups, individuals with stroke showed greater MAR compared to the older adults. Arm impairment, lesion volume, age, time since stroke, and preferential arm use were not different between the PA stroke groups, suggesting that motor impairment severity and extent of brain damage did not drive differences in PA.

Conclusion

Individuals who have had a stroke and are also physically active display lower MAR (i.e., similar myelin in both hemispheres) in motor regions. High levels of PA may be neuroprotective and mitigate myelin asymmetries once a neurological insult, such as a stroke, occurs. Alternately, it is possible that promoting high levels of PA after a stroke may reduce myelin asymmetries.

Keywords

Chronic stroke, myelin water fraction, physical activity, asymmetry ratios, older adults

Introduction

Due to a reduction in mortality rates, there are an increasing number of individuals living with long-term disabilities post-stroke. Consequently, people with stroke have the highest need for rehabilitation among neurological disorders worldwide.¹ Identifying effective interventions that optimize recovery of motor function represents an important challenge to improve quality of life after stroke.

Inducing myelin plasticity has become a viable therapeutic target for improving recovery after stroke.^2,3 White matter plays a crucial role in the formation and function of neural circuits^4,5 and undergoes use-dependent plasticity in young^6,7 and older⁸ adults. However, following a stroke, there is considerable loss of myelin in both the contra- and ipsilesional hemispheres,^9-11 which contributes to sensorimotor deficits.^2,9,12 Specifically, myelin asymmetry ratios (MARs), calculated as a ratio of contralesional to ipsilesional myelin water fraction, in the posterior limb of the internal capsule are greater (e.g., >1 and therefore less symmetrical) in individuals who have had a stroke compared with older adults.¹¹ Additionally, there is a negative relationship between MAR in the precentral gyrus⁹ and corticospinal tract^13,14 and upper-extremity motor impairment. Approaches that target and reduce MAR may also improve function after stroke.

Physical activity (PA) induces white matter plasticity. In animal models, exercise increased myelin debris removal and enhanced remyelination in chronic cerebral hypoperfusion rats,¹⁵ and increased the rate of remyelination after a demyelinating injury.¹⁶ In older adults, there is a positive relationship between white matter structure in the fornix, temporal, and frontal brain regions and amount of PA.^17,18 Further, aerobic exercise and resistance training increases white matter volume in the prefrontal cortex¹⁹ and decreases white matter lesion volume,²⁰ respectively. Taken together, PA appears to be a promising, cost-effective approach to promote white matter plasticity in older adults. An open question, however, is whether individuals who are more physically active have more symmetrical MAR (i.e., values close to 1). Yet, PA is often obtained through self-report questionnaires, which are subjective and may not accurately reflect real-world activity.²¹

The current study investigated MAR (contralesional/ipsilesional or dominant/non-dominant hemispheres) from five motor regions of interest (ROIs) in low and high physically active individuals with chronic stroke (>6 months) and older adults. Physical activity levels were obtained using accelerometers which participants wore for 72 consecutive hours (3 days). We hypothesized that: (1) individuals with stroke would display greater MAR (i.e., >1) relative to older adults, and (2) individuals in the lower PA stroke group would display greater MAR in motor ROIs relative to individuals in the higher PA stroke group as well as the older adult group.