Motor Impairments Related to Brain Injury Timing in Early Hemiparesis. Part II

Abstract

Background Extensive neuromotor development occurs early in human life, and the timing of brain injury may affect the resulting motor impairment. In part I of this paper series it was demonstrated that the distribution of weakness in the upper extremity depended on the timing of brain injury in individuals with childhood-onset hemiparesis. Objective The goal of this study was to characterize how timing of brain injury impacts joint torque synergies, or losses of independent joint control. Method Twenty-four individuals with hemiparesis were divided into three groups based on the timing of their injury: before birth (PRE-natal, n=8), around the time of birth (PERI-natal, n=8) and after 6 months of age (POST-natal, n=8). Individuals with hemiparesis, as well as 8 typically developing peers participated in maximal isometric shoulder, elbow, wrist, and finger torque generation tasks while their efforts were recorded by a multiple degree-of-freedom load cell. Motor output in 4 joints of the upper extremity were concurrently measured during 8 primary torque generation tasks to quantify joint torque synergies. Results There were a number of significant coupling patterns identified in individuals with hemiparesis that differed from the typically developing group. POST-natal differences were most noted in the coupling of shoulder abductors with elbow, wrist, and finger flexors, while the PRE-natal group demonstrated significant distal joint coupling with elbow flexion. Conclusion The torque synergies measured provide indirect evidence for the use of bulbospinal pathways in the POST-natal group, while those with earlier injury may utilize relatively preserved ipsilateral corticospinal motor pathways.

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