Spinal Regulation of Posture: Effects of Transcutaneous Spinal Cord and Affective Sound Stimulation

The combined effects of transcutaneous electrical stimulation (tES) of the spinal cord and affective sound stimulation on postural control were investigated to elucidate the involvement of spinal networks in the maintenance of vertical stability. Healthy volunteers (n = 27) underwent tES and sound stimulation separately and combined quasi-randomly. All participants were field-dependent; i.e., participants used the exteroceptive afferent stream for spatial orientation. Centre-of-pressure parameters were analysed to assess postural stability. Results showed that tES at the T11-T12 vertebrae stabilised posture, tES at the L1-L2 vertebrae had no postural effect, and sound stimulation from the left destabilised posture. To assess the role of spinal regulation of postural disturbances, we compared the effects of combined tES with sound stimulation to those of sound stimulation alone. Stimulation at the T11-T12 level reduced the lateral sway induced by affective sounds, whereas L1-L2 tES did not. These results suggest that, in healthy individuals, spinal networks located at the T11-T12 and L1-L2 vertebral levels have distinct roles in maintaining upright posture, both when a person is standing still and when they are actively stabilising their posture during destabilising perturbations. T11-T12 spinal networks stabilise upright posture when destabilising information is solely transmitted from the supraspinal level.