A Learning Process Which Improves Symmetry in the Dynamics of Thoracic Rotation: A New Hope for the Amelioration of Motor Disabilities

Abstract

Intersegmental joint dynamics permit generalisability: that is, a combination of joints to achieve maximum attainable amplitude of one degree of freedom. Generalisability contains the information to configure all lesser amplitudes using many degrees. This paper describes a treatment to reduce asymmetry in thoracic rotation, which appears to cause motor disabilities and pain. It proposes a learning process to recalibrate the neuromuscular system. The treatment is based on classical conditioning in which actors receive instructions to control a specific coordinate of the dominant hand-the conditioned stimulus (CS)-to be paired with a tensile force-the unconditioned stimulus (US). This pairing of CS with US generates a sequence of events, the conditioned response (CR). To facilitate control, the hand first reaches the target position constraining the overall degrees of freedom to just one. This reduces the burden on the CNS to deal with the indeterminacy of limb lengths, the regulation of joint rotation and the combination of multiple joints for performing the motor task. The dynamics of this CR generates coupling, comparable to the dynamics described in coupling of posture and gait. To verify the theory: in Experiment 1, thirteen participants with acute motor impairment received three treatments; in Experiment 2, twenty-six healthy participants were randomly assigned into two groups to perform the experimental treatment with the dominant or the non-dominant hand, respectively, for comparison. Seven variables were measured: four ranges of motion, two perceived efforts, and one pain. In Groups 2 and 3, the improvement in thoracic symmetry was significant. The treatment is able to trigger a mechanism that detects a critical value and initiates a transition from the dynamics of the action system and task constraints to a default value. Additionally, the treatment is highlighted as a neuromodulation impacting muscle tone with long-lasting amelioration of motor disabilities and pain.