Where Is Your Arm? Variations in Proprioception Across Space and Tasks

Abstract

The sense of limb position is crucial for movement control and environmental interactions. Our understanding of this fundamental proprioceptive process, however, is limited. For example, little is known about the accuracy of arm proprioception: Does it vary with changes in arm configuration, since some peripheral receptors are engaged only when joints move toward extreme angles? Are these variations consistent across different tasks? Does proprioceptive ability change depending on what we try to localize (e.g., fingertip position vs. elbow angle)? We used a robot exoskeleton to study proprioception in 14 arm configurations across three tasks, asking healthy subjects to 1) match a pointer to elbow angles after passive movements, 2) match a pointer to fingertip positions after passive movements, and 3) actively match their elbow angle to a pointer. Across all three tasks, subjects overestimated more extreme joint positions; this may be due to peripheral sensory signals biasing estimates as a safety mechanism to prevent injury. We also found that elbow angle estimates were more precise when used to judge fingertip position versus directly reported, suggesting that the brain has better access to limb endpoint position than joint angles. Finally, precision of elbow angle estimates improved in active versus passive movements, corroborating work showing that efference copies of motor commands and alpha-gamma motor neuron coactivation contribute to proprioceptive estimates. In sum, we have uncovered fundamental aspects of normal proprioceptive processing, demonstrating not only predictable biases that are dependent on joint configuration and independent of task but also improved precision when integrating information across joints.

Perception of the end position of a limb loaded with a weight

“…Recent studies have reported that the proprioceptive position sense is more precise when the perceiver's hand is closer to the body (Wilson, Wong, & Gribble, 2010) or when there is a weak correlation between the degree of error of the perceived fingertip position and the distance from the fingertip to other body parts (head and shoulder) (Fuentes & Bastian, 2010). However, these studies did not report that fingertip position is generally underestimated depending on relative distance from fingertip to other body parts.…”

“…Previous studies, however, have already reported that the end position (e.g., fingertip position or the end position of a fisted hand) is underestimated to some extent in static and no-weight conditions (Fuentes & Bastian, 2010;Longo et al, 2009;McDonnell, Scott, Dickison, Theriault, & Wood, 1989;Wann & Ibrahim, 1992). Humans would have a general tendency to underestimate the end position of the limb, even when it is statically held.…”

Potential of robots as next-generation technology for clinical assessment of neurological disorders and upper-limb therapy

“…Even a relatively simple task such as the limb-matching task in Dukelow et al [73] requires several different processes or brain structures to be functional: (1) the left cerebral hemisphere must sense the position of the right limb moved by the robot, (2) this proprioceptive information computed must be transferred to right cerebral hemisphere, (3) the right cerebral hemisphere must plan and control the movement of the left limb, (4) the right hemisphere must sense the final position of the left limb, and (5) the two hemispheres must work together to compare the position of both limbs. Further, tests could be developed to separate these factors such as to move the limb to a spatial location temporarily with the robot and then the subject could be asked to replicate this position with the same limb [75].…”

Cutaneous mechanisms of isometric ankle force control

“…Moreover, microneurographic studies suggest that cutaneous afferents can potentially encode position information about hand (Edin and Abbs 1991), knee (Edin 2001) and ankle (Aimonetti et al 2007) movements. Cutaneous input may also have a role in biasing position sense at extreme joint positions where the skin is most stretched (Fuentes and Bastian 2010).…”