Effects of Perturbation Velocity, Direction, Background Muscle Activation, and Task Instruction on Long-Latency Responses Measured From Forearm Muscles

Abstract

The central nervous system uses feedback processes that occur at multiple time scales to control interactions with the environment. The long-latency response (LLR) is the fastest process that directly involves cortical areas, with a motoneuron response measurable 50 ms following an imposed limb displacement. Several behavioral factors concerning perturbation mechanics and the active role of muscles prior or during the perturbation can modulate the long-latency response amplitude (LLRa) in the upper limbs, but the interactions among many of these factors had not been systematically studied before. We conducted a behavioral study on thirteen healthy individuals to determine the effect and interaction of four behavioral factors – background muscle torque, perturbation direction, perturbation velocity, and task instruction – on the LLRa evoked from the flexor carpi radialis (FCR) and extensor carpi ulnaris (ECU) muscles after velocity-controlled wrist displacements. The effects of the four factors were quantified using both a 0D statistical analysis on the average perturbation-evoked EMG signal in the period corresponding to an LLR, and using a timeseries analysis of EMG signals. All factors significantly modulated LLRa, and their combination nonlinearly contributed to modulating the LLRa. Specifically, all the three-way interaction terms that could be computed without including the interaction between instruction and velocity significantly modulated the LLR. Analysis of the three-way interaction terms of the 0D model indicated that for the ECU muscle, the LLRa evoked when subjects are asked to maintain their muscle activation in response to the perturbations was greater than the one observed when subjects yielded to the perturbations (p < 0.001), but this effect was not measured for muscles undergoing shortening or in absence of background muscle activation. Moreover, higher perturbation velocity increased the LLRa evoked from the stretched muscle in presence of a background torque (p < 0.001), but no effects of velocity were measured in absence of background torque. Also, our analysis identified significant modulations of LLRa in muscles shortened by the perturbation, including an interaction between torque and velocity, and an effect of both torque and velocity. The time-series analysis indicated the significance of additional transient effects in the LLR region for muscles undergoing shortening.

Grip force makes wrist joint position sense worse

“…As a result, pain can impair proprioception both in the peripheral and central nervous systems. Another possible source of the reposition errors considered here was the increased muscle stiffness ( Holmes et al, 2015 ; Weinman et al, 2021 ; Mannella et al, 2022 ). Increased muscle stiffness during grip-strength tasks may change proprioceptive receptor responses, such as the responses of the muscle spindles, which would impact the wrist joint position sense ( Gregory et al, 1988 ; Bower et al, 2006 ; Holmes et al, 2011 ; Naderi et al, 2020 ).…”

“…Other studies have focused on determining how a constant grip force affects wrist joint ROM ( Marshall et al, 1999 ; Dimartino et al, 2004 ) and found that as grip force increased, wrist joint ROM decreased. Increasing grip force was also considered one determinant of wrist stiffness ( Holmes et al, 2015 ; Weinman et al, 2021 ; Mannella et al, 2022 ).…”