Cutaneous stimulus registration and information processing differ during constant finger force and position

Introduction

　During static muscle contractions, there are two load types: maintenance of a joint angle against internal and external forces (position-control task) and maintenance of a constant force against a rigid resistance (force-control task). Previous studies have reported that heteronymous monosynaptic Ia facilitation was greater while homonymous inhibition was smaller in the position-control task as compared to the force-control task, even though a similar net torque was generated in both tasks. However, a difference in afferent cutaneous processing between these two tasks has not been fully understood. The aim of this study was to determine whether cutaneous stimulus registration and information processing differ between these two tasks by investigating the amplitude of cutaneomuscular reflex (CMR) and the gating of somatosensory evoked potentials (SEPs).

Methods

Eighteen healthy participants performed position- and force-control tasks with matched loads (20 % maximum voluntary contraction) with the right index finger. During each task, electrical stimulation was applied to the right index finger, and CMR and SEPs were recorded from the right first dorsal interosseous muscle and C3’ of the International 10–20 system, respectively.

Results

The E2 amplitude of CMR and the reduction of N33 amplitude of SEPs were greater in force-control than position-control task.

Conclusions

These results suggest that processing of cutaneous sensation is enhanced in force-control than position-control task, and, together with the previous study demonstrating the greater proprioceptive sensory processing in the position-control task, this study may contribute to the development of rehabilitation exercise programs.