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Abstract

In order to successfully move through the environment, the brain must maintain an accurate representation of the state of the musculoskeletal system. This sense is known as proprioception. Of particular relevance for movement control are the senses of position and movement, which are often collectively referred to as kinesthesia. Muscle spindles, which are embedded within skeletal muscle, are thought to be the primary receptors underlying kinesthetic perception. One way to probe the contribution of muscle spindles to motor control is to perturb their afferent output using tendon vibration. The overarching goal of this thesis was to understand how the central nervous system (CNS) uses proprioceptive feedback from muscles to estimate limb state. Specifically, by using tendon vibration to bias muscle spindle afferent input, this work aimed to gain insight into how spindle feedback contributes to limb state estimation during goal-directed movement and perception. Chapters 2–4 examined how muscle spindle feedback is used to estimate limb state during goal-directed reaching movements. Chapter 5 investigated whether task constraints modify how proprioceptive feedback is utilized, by comparing tasks that differ in their reliance on predictive versus corrective control. Chapter 6 used tendon vibration to examine how the CNS responds to persistent proprioceptive errors, and whether such errors can drive sensorimotor recalibration when veridical visual feedback is available. Across studies, this thesis provides evidence that proprioceptive feedback is not treated as a single homogeneous signal. Instead, the CNS appears to combine muscle spindle feedback from multiple muscles in a weighted manner, such that feedback from different muscles does not contribute equally to the estimate of limb state. A key finding is that the CNS consistently prioritizes feedback that is more reliable given the biomechanical and task context. This weighting pattern was observed across goal-directed reaching tasks as well as perceptual alignment tasks. Finally, the results from Chapter 6 suggest that the CNS does not respond uniformly to visual–proprioceptive discrepancies, and that the expression of recalibration depends on whether the error is induced through visual feedback or proprioceptive feedback.