Perception and control of upper limb movement: Insights gained by analysis of sensory and motor variability

Abstract: Chronic neck-shoulder pain is associated with impairments of proprioception and motor control. Thus, assessment of proprioceptive and motor function may be powerful tools both for research and clinical practice. However, insufficient knowledge of certain features of human sensorimotor control hampers both development and interpretation of results of clinically relevant tests. For example, evidence is lacking which proprioception submodalities are reflected in common tests of proprioception. For testing motor function, a better understanding of the control of goal directed arm movements is needed. The purpose of the thesis was to gain further insights into the sensorimotor control of the upper limb in healthy subjects, with implications for clinical testing. The main aims were: (1) to study relationships of outcomes of different tests of shoulder proprioception and (2) to study control strategies in bimanual pointing tasks by analysis of the structure of joint angle variability with the Uncontrolled Manifold (UCM) method. Correlations between proprioceptive acuity in different variants of ipsilateral position-matching and velocity-discrimination were studied. The main finding was that two uncorrelated mechanisms based either on perception of position or movement might underlie perception of limb location in ipsilateral position-matching. The results provided important information for interpretation of common and development of novel tests of shoulder proprioception. The structure of joint angle variance was computed with respect to several task variables during bimanual pointing. Joint angle variability was decomposed in variance affecting and not affecting a task variable. The results showed that the variance in joint space was structured according to the predictions of the UCM hypothesis. It was also shown that the arms were united into one synergy to significantly larger degree than joints within each arm were united into single-arm synergies. It was concluded that the UCM approach might quantify components of motor variability during repetitive motor tasks.