Abstract
Proprioceptive signals from peripheral mechanoreceptors form the basis for bodily perception and are known to be essential for motor control. However we still have an incomplete understanding of how proprioception differs between joints, whether it differs among the various degrees-of-freedom (DoFs) within a particular joint, and how such differences affect motor control and learning. We here introduce a robot-aided method to objectively measure proprioceptive function: specifically, we systematically mapped wrist proprioceptive acuity across the three DoFs of the wrist/hand complex with the aim to characterize the wrist position sense. Thirty healthy young adults performed an ipsilateral active joint position matching task with their dominant wrist using a haptic robotic exoskeleton. Our results indicate that the active wrist position sense acuity is anisotropic across the joint, with the abduction/adduction DoF having the highest acuity (the error of acuity for flexion/extension is 4.64 ± 0.24°; abduction/adduction: 3.68 ± 0.32°; supination/pronation: 5.15 ± 0.37°) and they also revealed that proprioceptive acuity decreases for smaller joint displacements. We believe this knowledge is imperative in a clinical scenario when assessing proprioceptive deficits and for understanding how such sensory deficits relate to observable motor impairments.
Highlights
Proprioceptive signals originate from mechanoreceptors within muscles, tendons, and skin, which give rise to kinaesthesia and the sense of joint position
If proprioceptive acuity during active matching differed for the three tested DoF, we investigated the matching error and the variability
A subsequent post-hoc analysis showed that Abduction/Adduction yielded the highest acuity (ME = 3.68 ± 0.32°), and was significantly different from FE (ME = 4.64 ± 0.24°, post hoc Fisher test, p = 0.040) and PS (ME = 5.15 ± 0.37°, Fisher, p = 0.0018), while no significant difference was found between FE and PS
Summary
Proprioceptive signals originate from mechanoreceptors within muscles, tendons, and skin, which give rise to kinaesthesia (the sense of limb movement) and the sense of joint position. These afferent signals are crucial for bodily awareness, but they have great impact on voluntary motor control, and on the regulation of muscle tone and postural stability [1,2,3,4]. The JPM measures the accuracy in replicating a joint angle in absence of vision [13], while the PTM quantifies subject’s sensitivity in discriminating the largest amplitude between two passive movements [14]
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