Abstract
A deep investigation of proprioceptive processes is necessary to understand the relationship between sensory afferent inputs and motor outcomes. In this work, we investigate whether and how perception of wrist position is influenced by the direction along which the movement occurs. Most previous studies have tested Joint Position Sense (JPS) through 1 degree of freedom (DoF) wrist movements, such as flexion/extension (FE) or radial/ulnar deviation (RUD). However, the wrist joint has 3-DoF and many activities of daily living produce combined movements, requiring at least 2-DoF wrist coordination. For this reason, in this study, target positions involved movement directions that combined wrist flexion or extension with radial or ulnar deviation. The chosen task was a robot-aided Joint Position Matching (JPM), in which blindfolded participants actively reproduced a previously passively assumed target joint configuration. The JPM performance of 20 healthy participants was quantified through measures of accuracy and precision, in terms of both perceived target direction and distance along each direction of movement. Twelve different directions of movement were selected and both hands tested. The left and right hand led to comparable results, both target extents and directions were differently perceived according to the target direction on the FE/RUD space. Moreover, during 2-DoF combined movements, subjects’ perception of directions was impaired when compared to 1-DoF target movements. In summary, our results showed that human perception of wrist position on the FE/RUD space is symmetric between hands but not isotropic among movement directions.
Highlights
Proprioception is the multimodal perceptual process that allows humans to maintain global awareness of their body position during active or passive movements
Sensory signals coming from receptors located in joints, muscles, tendons and skin, are encoded biomechanically and transmitted to the Central Nervous System (CNS), which carries out multi-sensory association, Wrist Position Sense Symmetric Anisotropy allowing individuals to be aware of their body posture, position in space, movements and applied forces
These results are important for the formulation of the Joint Position Matching (JPM) task, because the position of the JPM targets were normalized with respect to the evaluated range of motion (ROM), setting a target distance equal to 80% of the assessed ROM
Summary
Proprioception is the multimodal perceptual process that allows humans to maintain global awareness of their body position during active or passive movements. Sensory signals coming from receptors located in joints, muscles, tendons and skin, are encoded biomechanically and transmitted to the Central Nervous System (CNS), which carries out multi-sensory association, Wrist Position Sense Symmetric Anisotropy allowing individuals to be aware of their body posture, position in space, movements and applied forces. Different receptors provide different facets of proprioceptive information: Golgi-type endings detect forces and tensile strain at the limit of the range of motion (Oksuz et al, 2018); Ruffinitype mechanoreceptors, typically present in wrist ligaments, are likely to be involved in the perception of both wrist positions and motions (Hagert et al, 2005); Pacini corpuscles, more rarely identified, are sensitive to the onset, offset and velocity of motions, suggesting that this information is probably less important for sensorimotor processes; muscle spindles, located in intrafusal muscle fibers, provide information about muscle length and speed of muscle stretch. The influence of both neural mechanisms (Marini et al, 2019) and intrinsic wrist mechanical properties (Albanese et al, 2019; Falzarano et al, 2020) on proprioceptive processes has still been poorly investigated
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