Abstract
Tasks of daily life require the independent use of the arms and hands. Individuals with hemiparetic cerebral palsy (HCP) often experience difficulty with fine motor tasks demonstrating mirrored movements between the arms. In this study, bilateral muscle activations were quantified during single arm isometric maximum efforts and submaximal reaching tasks. The magnitude and direction of mirrored activation was examined in 14 individuals with HCP and 9 age-matched controls. Participants generated maximum voluntary torques (MVTs) in five different directions and completed ballistic reaches while producing up to 80% of shoulder abduction MVT. Electromyography (EMG) signals were recorded from six upper extremity muscles bilaterally. Participants with HCP demonstrated more mirrored activation when volitionally contracting the non-paretic (NP) arm than the paretic arm (F = 83.543, p < 0.001) in isometric efforts. Increased EMG activation during reach acceleration resulted in a larger increase in rest arm co-activation when reaching with the NP arm compared to the paretic arm in the HCP group (t = 8.425, p < 0.001). Mirrored activation is more pronounced when driving the NP arm and scales with effort level. This directionality of mirroring is indicative of the use of ipsilaterally terminating projections of the corticospinal tract (CST) originating in the non-lesioned hemisphere. Peripheral measures of muscle activation provide insight into the descending pathways available for control of the upper extremity after early unilateral brain injury.
Highlights
Mirror movements in the arm are defined as involuntary mimicking of voluntary movement of the contralateral arm (Green, 1967; Woods and Teuber, 1978; Nelles et al, 1998; Riddell et al, 2019)
A principle exception to this typical progression is a unilateral lesion to the developing brain such as a perinatal stroke resulting in hemiparetic cerebral palsy (HCP)
In the static tasks, mirrored activation ratios were larger in individuals with HCP compared to the TD group when contracting the NP arm but not when contracting the paretic arm
Summary
Mirror movements in the arm are defined as involuntary mimicking of voluntary movement of the contralateral arm (Green, 1967; Woods and Teuber, 1978; Nelles et al, 1998; Riddell et al, 2019). Independent control of the arm is refined and mirroring diminishes with age (Woods and Teuber, 1978; Koerte et al, 2010) as typical nervous system maturation prunes descending motor pathways. This process results in contralateral connections of over 80% of the Between-Limb Muscle Co-activation in HCP corticospinal tract (CST) and loss of ipsilaterally terminating projections. The alternative connectivity patterns of descending pathways from the interruption to the typical development of the CST could result in a persistence of mirror movements (Eyre et al, 2001; Staudt, 2010; Jaspers et al, 2015). Mirror movements were documented in 1978 during a supination task in children with hemiplegia, most prominently seen in participants with lesions occurring before 1 year of age (Woods and Teuber, 1978)
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