Asymmetric vestibular stimulation and unilateral neck muscle vibration or contraction induce long-term effects on self-motion perception

Abstract

Background The effect of neck proprioception was tested on self-motion perception elicited by asymmetric whole-body yaw oscillations in the dark, in the hypothesis that intense and repetitive activation of neck proprioceptive system induces immediate and sustained effects on vestibular-dependent motion perception. Methods Oscillation consisted of two half-sinusoidal cycles of equal amplitude (40°) but different duration, featuring a fast (FHC) and slow half-cycle (SHC). Motion perception was estimated by subjects tracking with a pointer the remembered position of an earth-fixed visual target. Results Asymmetric vestibular stimulation induced a progressive bias in motion perception, whereby the gain of the tracking response gradually increased during FHC and decreased during SHC. In few cycles, body position was perceived displaced toward the fast rotation side. This error was influenced by static head position relative to trunk and neck muscle vibration. Active head deviation superimposed to the asymmetric oscillation enhanced movement perception for head turned toward the side of fast rotation and decreased it for opposite direction. Vibration of the neck muscles splenius capitis or sternocleidomastoideus differentially influenced the perceived rotation during asymmetric oscillation. The error in target representation was modified not only during on-going vibratory stimulation, but also after it. After-effects endured minutes and hours depending on vibration frequency and duration. Larger and longer-lasting effects were associated with high-frequency vibration and isometric-contraction of vibrated muscle. The effect on perception was consolidated or cancelled by added vibration trains of 100 and 5 Hz, respectively. Conclusions The intense vibratory post-effect suggests that activation of neck proprioceptors induces plastic changes along proprioceptive and vestibular networks responsible for motion perception, and enhance motion perception in the direction of the head deviation.