Neck muscle vibration disrupts steering of locomotion

Neck muscle vibration was applied to human subjects to assess the influence s of neck abnormal proprioceptive input on the organization and execution o f gait. Subjects walked blindfolded to a previously seen target, located st raight ahead at similar to4 m. Vibration was applied on the right side of t he neck, both during and before walking. The variables measured were length , duration, and velocity of trajectory; relative and absolute frontal error s at target; and width of walking support base. Vibration applied during lo comotion produced an undershoot of target and deviation of gait trajectory toward the side opposite to vibration. Vibration applied before locomotion produced no effect on length of trajectory but slowing of velocity and nons ystematic deviation. When vibration frequency was increased, the amplitude of the nonsystematic deviation increased. Vibration applied during or befor e stance trials had minor effects on body sway. Vibration before stance had no effect on the position of mean center of foot pressure, whereas vibrati on during stance displaced it to the side opposite to the vibrated muscle. We suggest that vibration during locomotion reduces length and velocity of trajectory because of a direct action on the locomotor centers and produces trajectory deviation related to its effect on stance. Vibration before loc omotion causes a major, nonsystematic deviation from the planned trajectory , possibly connected to a disorientation of the internal references.