Effects of Concussion on Sensorimotor Adaptation to Unpredictable Spring-Like Loads: A Pilot Study

We examined how concussion impacts sensorimotor memories used to adapt goal-directed reaches to unpredictable hand-held loads. Recently concussed individuals underwent computerized cognition testing and a robotic test of sensorimotor adaptation as soon as possible after injury, on return to activity, and after three months. Control subjects were tested at similar intervals. During robotic testing, subjects moved a robot handle repeatedly between two targets; the handle resisted movement with spring-like forces that changed unpredictably between trials, allowing us to model how performance memories contribute to trial-by-trial adaptation. Because symptom severity varied markedly at Session 1, we bisected the concussed cohort based on initial reaction time. Although Session 1 data revealed abnormally high limb compliance estimates in more severely concussed individuals relative to controls, we did not find group differences in how memories contribute to adaptation in any session. However, control group models revealed a practice effect affecting memory model coefficients; this may have masked concussion's initial effects on how memories contribute to adaptation. Although a practice effect and a heterogeneous concussed cohort preclude strong conclusions, our study demonstrates feasibility of the robotic assessment and indicates procedural improvements that may increase its sensitivity and specificity to concussion-related changes in how memories contribute to adaptation.