Directional postural responses induced by vibrotactile stimulations applied to the torso.

It has been shown that torso-based vibrotactile feedback significantly reduces postural sway in balance-compromised adults during quiet standing and in response to perturbations. This study aimed to determine whether vibrotactile stimulations applied to different torso locations induced directional postural responses and whether torso cutaneous information contributes to body representation. Eleven healthy young adults equipped with an inertial measurement unit (IMU) placed on the torso were asked to maintain an upright posture with closed eyes. Six vibrators (tactors) were placed on the torso in contact with the skin over the left and right external oblique, internal oblique, and erector spinae muscles at the L4/L5 level. Each tactor was randomly activated four times per location at a frequency of 250 Hz for a period of 5 s. The IMU results indicated that vibration applied individually over the internal oblique and erector spinae muscles induced a postural shift of about one degree oriented in the direction of the stimulation, while simultaneous activation of all tactors and activation of tactors over external oblique muscles produced insignificant postural effects. The root mean square of the sway signal was significantly higher during vibration than before or after. However, the center of pressure displacement, measured by a force plate, was uninfluenced by any vibration. These results suggest a multi-joint postural response including a torso inclination associated with vibration-induced changes in cutaneous information. The directional aspect of vibration-induced postural shifts suggests that cutaneous information from the stimulated areas contributes to proprioception and upper body spatial representation.