Use of galvanic vestibular feedback to control postural orientation in decerebrate

31 32 In quadrupeds, the dorsal-side-up body orientation during standing is maintained due to a 33 postural system that is driven by feedback signals coming mainly from limb mechanoreceptors. 34 In caudally decerebrated (postmammillary) rabbits, the efficacy of this system is considerably 35 reduced. In this paper we report that the efficacy of postural control in these animals can be 36 restored with galvanic vestibular stimulation (GVS) applied transcutaneously to the labyrinths. 37 In standing intact rabbits, GVS causes a lateral body sway towards the positive electrode. We 38 used this GVS-caused sway to counteract the lateral body sway resulting from a mechanical 39 perturbation of posture. Experiments were performed on postmammillary rabbits that stood on 40 the tilting platform with their hindlimbs. To make the GVS value dependent on the postural 41 perturbation (i.e., on the lateral body sway caused by tilt of the platform), an artificial feedback 42 loop was formed in the following way: 1) Information about the body sway was provided by a 43 mechanical sensor; 2) The GVS current was applied when the sway exceeded a threshold value; 44 the polarity of the current was determined by the sway direction. This simple algorithm allowed 45 the “hybrid” postural system to maintain the dorsal-side-up orientation of the hindquarters when 46 the platform was tilted by ±20°. Thus, an important postural function, i.e., securing lateral 47 stability during standing, can be restored in decerebrate rabbits with the GVS-based artificial 48 feedback. We suggest that such a control system can compensate for the loss of lateral stability 49 of various etiologies, and can be used for restoration of balance control in patients with impaired 50 postural functions. 51