A cutaneous positioning system

Our previous work revealed that torso cutaneous information contributes to the internal representation of the torso and plays a role in postural control. Hence, the aims of this study were to assess whether posture could be manipulated by patterns of vibrotactile stimulation and to determine whether resulting modified postures were associated with specific and consistent spatial attitudes. Ten healthy young adults stood in normal and Romberg stances with six vibrating actuators positioned on the torso in contact with the skin over the anatomical locations corresponding to left and right external oblique, internal oblique and erector spinae muscles at the L4/L5 vertebrae level. A 250-Hz tactile vibration was applied for 5 s either at a single location or consecutively at each location in clockwise or counterclockwise sequences. Kinematic analysis of the body segments indicated that postural responses observed in response to single and sequential stimulation patterns were similar, while the center of pressure remained unaltered in any situations. Moreover, torso inclinations followed rectilinear-like path segments chartered by stimuli loci during sequential stimulations. Comparison of torso attitudes with previous results obtained with co-vibration patterns of the same duration showed that torso inclination amplitudes are equivalent for single (one location) and co-vibration (pairs of locations) patterns inducing the same directional effect. Hence, torso cutaneous information exhibits kinesthetic properties, appears to provide a map of upper body spatial configuration, and could assume the role of an internal positioning system for the upper body.