Signals of motor command bias joint position sense in the presence of feedback from proprioceptors

Abstract

Joint position sense is believed to be mediated by muscle afferent signals. Because a "phantom" hand produced by a sensory and motor nerve block appears to move in the direction of voluntary effort, signals of "motor command" or "effort" can influence perceived joint position. To determine whether this occurs when sensory signals are available, three studies assessed position sense when motor command and afferent signals were available, but joint movement was prevented. First, the hand was positioned to stop movement at the proximal joint of the middle finger, and movement at the distal joint was impossible because the muscles had been "disengaged". Voluntary efforts produced illusory position changes in the direction of the effort (12.6 +/- 2.0 degrees distal joint; 12.3 +/- 2.3 degrees proximal joint for efforts at 30% maximum; means +/- SD). Second, when subjects attempted to move the index finger under isometric conditions, the index finger appeared to move 7.4 +/- 1.2 degrees in the direction of efforts. These illusions graded with the level of effort (10 or 30% maximum) and far exceeded any real joint movement. Finally, because changes in muscle afferent feedback might have accompanied the voluntary efforts, all forearm and hand muscles were completely paralyzed by locally infused rocuronium. During paralysis, passive wrist position was signaled accurately, but, during attempted efforts (30% maximum), perceived wrist position changed by 9.7 +/- 4.9 degrees . Before paralysis, isometric efforts changed it by 6.7 +/- 3.6 degrees . Thus all studies concur: when joint movement is prevented, signals of motor command contribute to joint position sense.

Proprioception 3 years after shoulder arthroplasty in 3D motion analysis: a prospective study

“…As Smith et al [22] reported, these signals of motor command can bias joint position sense in the presence of feedback from proprioceptors.…”

Effect of gravity-like torque on goal-directed arm movements in microgravity

“…On the other hand, other works have insisted on the role of the central command necessary to overcome gravitational load in limb position sense (Gandevia et al 2006;Smith et al 2009;Walsh et al 2009). In the framework of the present experiment, however, it proves difficult to favor one hypothesis over the other.…”

The role of spinal manipulation in addressing disordered sensorimotor integration and altered motor control

“…Motor commands or motor intention (also known as ''efference copies'') are for example known to interact with afferent signals to generate sensation, and are known to contribute to joint position sense (Smith et al, 2009). Under normal circumstances there is an integration of intention, action and sensory feedback.…”