Developmental and acquired brain injury have opposite effects on finger coordination in children

Abstract

The ability to coordinate finger forces to dexterously perform tasks develops in children as they grow older. Following brain injury, either developmental (as in cerebral palsy-CP) or acquired (as in traumatic brain injury-TBI), this developmental trajectory will likely be impaired. In this study, we compared finger coordination in a group of children aged 4-12 with CP and TBI to a group of typically developing children using an isometric pressing task. As expected, deficits were observed in functional tests (Jebsen Taylor test of hand function, Box and Block test) for both groups, and children in both groups performed the pressing task less well than the control group. However, differing results were observed between the CP and TBI groups when using the uncontrolled manifold hypothesis to look at the synergy index. This index measures the relative amount of "good" (does not affect the outcome measure) and "bad" (does affect the outcome measure) variability, where in this case the outcome measure is the total force produced by the fingers. While children with CP were more variable in their performance, their synergy index was not significantly different from typically developing children, suggesting the development of compensatory strategies. In contrast, the children following TBI showed performance that got worse as a function of age (i.e., the older children with TBI performed worse than the younger children with TBI). These differences between the groups may be a result of different areas of brain injury typically observed in CP and TBI, and the different amount of time that has passed since the injury.

Keywords: cerebral palsy; children; coordination; development; fingers; force; traumatic brain injury; uncontrolled manifold hypothesis.

FIGURE 1

Comparisons of the (A) maximum voluntary strength (MVC) data, (B) box and block test (C) Jebsen-Taylor test of hand function and (D) task performance—straight line deviation. The data from this experiment is compared to data from a previous study (the black stars). The black line is the predicted data for the control group, the dashed red line is the predicted data for the TBI group, and the dashed red line is the predicted data for the CP group, according to the tested models. The lines are only drawn when the differences between the groups was significant.

FIGURE 2

Uncontrolled manifold (UCM) analysis—(A) shows the good variance (that which doesn’t affect the outcome variable) (B) shows the bad variance (which does affect the outcome variable). (C) Shows the synergy index Δv. The black line is the predicted data for the control group, the dashed red line is the predicted data for the TBI group, and the dashed red line is the predicted data for the CP group, according to the tested models. The lines are only drawn when the differences between the groups was significant. The color of the points indicates the group. The black stars are data from typically developing children from a previous study.

FIGURE 3

Examples of force profiles. Each graph shows the forces applied by the four fingers in a single trial, with the black line showing the sum of the forces (which controlled the height of the object on the screen). (A) A younger child (aged 5) with TBI, Δv = −0.71, (B) a younger child (aged 5) with CP, Δv = −1.57, (C) an older child (aged 12) with TBI, Δv = −2.15, (D) an older child (aged 10) with CP, Δv = −0.77. When there is more positive covariation between the fingers, i.e., in panels (B,C), Δv tends to have lower values (more negative), while when negative covariation is observed, Δv tends to have higher values, i.e., in panels (A,D).