Stability of perception of the hand's aperture in a grasp.

KEY POINTS: How we judge the location of our body parts can be affected by a range of factors that change how our brain interprets proprioceptive signals. We examined the effect of several such factors on how we perceive an object's width and the spacing between our thumb and fingers when grasping. Grasp-related perceptions were slightly wider when using all digits, in line with our tendency to grasp larger objects with the entire hand. Surprisingly, these perceptions were not affected by the frames of reference for judgements (object width versus grasp aperture), whether the object was grasped actively or passively, or the strength of the grasp. These results show that the brain maintains a largely stable representation of the hand when grasping stationary objects. This stability may underpin our dexterity when grasping a vast array of objects. ABSTRACT: Various factors can alter how the brain interprets proprioceptive signals, leading to errors in how we perceive our body and execute motor tasks. This study determined the effect of critical factors on hand-based perceptions. In Experiment 1, 20 participants grasped without lifting an unseen 6.5 cm-wide object with two grasp configurations: thumb and all fingers, and thumb and index finger. Participants reported perceived grasp aperture (body reference frame) or perceived object width (external reference frame) using visual charts. In Experiment 2, 20 participants grasped the object with three grasp intensities (1, 5 and 15% maximal grasp force) actively or passively and reported perceived grasp aperture. A follow-up experiment addressed whether results from Experiment 2 were influenced by the external force applied during passive grasp. Overall, there was a mean difference of 0.38 cm (95% confidence interval (CI), 0.12 to 0.63) between the two grasp configurations (all digits compared to thumb and index finger). Perceived object width compared to perceived grasp aperture differed by only -0.04 cm (95% CI, -0.30 to 0.21). There was no real effect of grasp intensity on perceived grasp aperture (-0.01 cm; 95% CI, -0.03 to 0.01) or grasp type (active versus passive; 0.18 cm; 95% CI, -0.19 to 0.55). Overall, grasp-related perceptions are slightly wider when using all digits, in line with our tendency to grasp larger objects with the entire hand. The other factors - frame of reference, grasp intensity and grasp type - had no meaningful effect on these perceptions. These results provide evidence that the brain maintains a largely stable representation of the hand.

Neuromodulation of the Suprascapular Nerve.

Chronic intractable shoulder pain (CISP) is defined as shoulder pain which is present for longer than 6 months and does not respond to standard treatments like medication, physical therapy, rehabilitation, selective nerve blocks and local infiltrations, or orthopedic procedures. The etiology of CISP may be very diverse, varying from many orthopedic conditions to non-orthopedic conditions. The fact that the suprascapular nerve is one of the most important nerves supplying the shoulder region makes this nerve an interesting target in treating patients suffering shoulder pain. Invasive treatment options are peripheral nerve blocks, temporary electrical stimulation, and neurostimulation. To our best knowledge, thus far there are only a few reports describing the technique of permanent neurostimulation of the suprascapular nerve. In this article we present a patient suffering shoulder pain after she underwent surgery for cervical stenosis. After a step by step treatment protocol was done, we finally offered her trial stimulation of the suprascapular nerve. A single quad lead was implanted via a posterior approach under fluoroscopic and ultrasound guidance. Two weeks after successful stimulation, we implanted a permanent neuromodulation system. Permanent neurostimulation of the suprascapular nerve and its end branches may be a new interesting target in treating patients suffering shoulder pain due to various etiologies. In our patient the follow-up period is 9 months with an excellent result in pain relief, we observed no complications thus far, especially no dislocation or breakage of the lead. In this report, literature on this subject is reviewed, and our technique is well documented with additional anatomical illustrations.