Changing Motor Synergies in Chronic Stroke

TLDR

Synergies are fundamental components of vertebrate movement, and their disruption—particularly the inability to execute them in a timely and graded manner—impairs functional motor performance, a deficit that manifests as abnormal, loss‑of‑joint‑control synergies in chronic stroke patients. The study aimed to characterize how training alters synergies, determining whether recovery involves augmentation of existing abnormal synergies or their extinction. Using a robotic therapy device, the authors trained and analyzed paretic arm movements in 117 chronic stroke participants. Robotic training led to improved circle drawing and increased shoulder–elbow independence, indicating that the observed kinematic changes—attributable to tuning rather than extinction of abnormal synergies—account for a significant portion of functional recovery as measured by the Fugl‑Meyer scale.

Abstract

Synergies are thought to be the building blocks of vertebrate movements. The inability to execute synergies in properly timed and graded fashion precludes adequate functional motor performance. In humans with stroke, abnormal synergies are a sign of persistent neurological deficit and result in loss of independent joint control, which disrupts the kinematics of voluntary movements. This study aimed at characterizing training-related changes in synergies apparent from movement kinematics and, specifically, at assessing: 1) the extent to which they characterize recovery and 2) whether they follow a pattern of augmentation of existing abnormal synergies or, conversely, are characterized by a process of extinction of the abnormal synergies. We used a robotic therapy device to train and analyze paretic arm movements of 117 persons with chronic stroke. In a task for which they received no training, subjects were better able to draw circles by discharge. Comparison with performance at admission on kinematic robot-derived metrics showed that subjects were able to execute shoulder and elbow joint movements with significantly greater independence or, using the clinical description, with more isolated control. We argue that the changes we observed in the proposed metrics reflect changes in synergies. We show that they capture a significant portion of the recovery process, as measured by the clinical Fugl-Meyer scale. A process of "tuning" or augmentation of existing abnormal synergies, not extinction of the abnormal synergies, appears to underlie recovery.