J Neurophysiol (November 1, 2002). 10.1152/jn.00198.2002
Submitted on 18 March 2002
Accepted on 15 July 2002

Neck Muscle Vibration and Spatial Orientation During Stepping in Place in Humans

 ¹Department of Experimental Medicine, Section of Human Physiology, University of Genoa, I-16132 Genoa, Italy;  ²Institut National de la Santé et de la Recherche Médicale, Motricité & Plasticité, University of Burgundy, F-21078 Dijon, France; and  ³Physiological Institute, University of Pavia, and Human Movement Laboratory, Fondazione Salvatore Maugeri, Istituto di Ricovero e Cura a Carattere Scientifico, I-27100 Pavia, Italy

Bove, Marco, Gregoire Courtine, and Marco Schieppati. Neck Muscle Vibration and Spatial Orientation During Stepping in Place in Humans. J. Neurophysiol. 88: 2232-2241, 2002. Unilateral long-lasting vibration was applied to the sternomastoid muscle to assess the influence of asymmetric neck proprioceptive input on body orientation during stepping-in-place. Blindfolded subjects performed 3 sequences of 3 trials, each lasting 60 s: control, vibration applied during stepping (VDS), and vibration applied before stepping (VBS). VDS caused clear-cut whole body rotation toward the side opposite to vibration. The body rotated around a vertical axis placed at about arm's length from the body. The rotation did not begin immediately on switching on the vibrator. The delay varied from subject to subject from a few seconds to about 10 s. Once initiated, the angular velocity of rotation was remarkably constant (about 1°/s). In VBS, at the beginning of stepping, subjects rotated for a while as if their neck were still vibrated. At a variable delay, the direction of rotation reversed, and the effects were opposite to those observed during VDS. Under no condition did head rotation, head roll, or lateral body tilt accompany rotation. The results confirm and extend the notion that the neck proprioceptive input plays a major role in body orientation during locomotion. The body rotation does not seem to depend on the same mechanisms that modify the erect posture; rather, the asymmetric neck input would seem to modify the egocentric body-centered coordinate system.