Carranza, E. | bioRxiv Science

bioRxiv2026

Cervical spinal cord stimulation disrupts proprioception yet improves voluntary arm reaching

Whether proprioception is necessary for upper-limb motor control has been debated for decades. Classic studies in deafferented animals and humans suggested that proprioception may be dispensable for rapid, goal-directed movements. However, chronic sensory loss conflates the absence of proprioceptive input with years of compensatory adaptation. As a result, the field has lacked a strong causal test of proprioceptions contribution to motor control. Here, we leveraged a clinical trial of cervical spinal cord stimulation (SCS) in individuals with chronic post-stroke hemiparesis to study if electrical stimulation of sensory afferents causally perturbs proprioception and affects arm reaching. We found that turning SCS ON causally impaired proprioceptive perception and postural stabilization in response to force perturbations, and enhanced adaptation to visual errors during implicit learning. Yet visually and non-visually rapid, goal-directed reaching improved in smoothness, straightness and spatial accuracy. These findings provide strong causal evidence that proprioception is not required for rapid, goal-directed action, helping resolve a decades-long debate regarding its necessity for effective movement.

bioengineering↗

bioRxiv2023

Understanding Age-Related Changes in Proprioception through Active and Passive Tasks

Voluntary control of motor actions requires precise regulation of proprioceptive and somatosensory functions. While aging has demonstrated to decline sensory processing functions, the effect of age on proprioception remains less clear. Indeed, previous studies contradict on whether passive proprioception (i.e., during externally driven movements) is affected over age. Moreover, no studies explored age-related modifications in active proprioception (i.e., during voluntary movements). Understanding these changes is critical to identify and prevent possible causes of reduced movement performances and mobility, in particular in age-related neurological conditions such as stroke or Parkinson disease. Here, we first refined a robotic protocol to assess upper-limb active proprioception and demonstrated the robustness and reliability of outcome measures over sessions. We then compared performances between young and elderly subjects during active and passive proprioceptive tasks. We found that while the two populations of subjects performed similarly in passive proprioception, elderly subjects acuity declined during active proprioception. Importantly, we confirmed that the decline could not be explained by impairments in voluntary motor control. Our data and robotic protocols further elucidate the debate over proprioception in elderly subjects and provide evidence that robust proprioceptive assessments should be an essential measurement in clinical settings. New & NoteworthyUpper limb position sense has been previously evaluated using passive matching protocols with the contralateral arm. These studies have found contradicting results regarding a possible decline in passive proprioception over age. Here we replicated this passive protocol and compared it to its active counterpart. Our results suggest that aging has an effect only in the active condition, leading to the hypothesis of a potential role of the cortico-spinal and cerebellar pathways in proprioception decline.

bioengineering↗