Data Sheet 1_Anterior–posterior and medial-lateral balance metrics are unchanged when two-dimensional pseudorandom motion perturbations are provided in semicircular canal coordinates.pdf

IntroductionExternal continuous perturbations using a motion platform have been developed by employing either sum-of-sines (SoS) or a pseudorandom ternary sequence (PRTS) of numbers to quantify body sway evoked in the medial-lateral (ML) or anterior-posterior (AP) directions, which ultimately helps understand the human postural control system. These stimuli have been provided via pitch tilts of the motion platform for evaluations of AP balance responses or roll tilts for ML balance responses. However, little is known about whether a healthy postural control system responds to 2-dimensional (2D) perturbations similarly when the perturbation stimuli are provided in semicircular canal coordinates (i.e., right-anterior/left-posterior (RALP) and left-anterior/right-posterior (LARP)) versus roll/pitch coordinates. Stimuli provided in either set of coordinates were orthogonal in both time and space. Our 2D platform perturbations provided in RALP/LARP coordinates will have the potential to better assess the contribution of each pair of the vertical semicircular canals to postural control for individuals with dysfunction of the vertical semicircular canals.
MethodsTo address this knowledge gap, we developed four different balance perturbation trajectories using sum-of-sines (SoS) signals and simultaneously provided those stimuli in (i) roll and pitch, (ii) RALP and LARP, and (iii) roll, pitch, RALP, and LARP dimensions. Center of pressure (CoP) data were collected from 24 healthy participants (40 13 years of age) on a commercially available motion platform (Virtualis Motion VR, Perault, France). A discrete Fourier transform (DFT) was applied to the CoP data to identify responses at perturbed frequencies (i.e., spectral response components).
ResultsWe found that ML and AP postural responses were not significantly different when the platform perturbations were simultaneously provided in RALP/LARP coordinates versus roll/pitch coordinates.
DiscussionThis finding suggests that our 2D platform perturbations in RALP/LARP coordinates allow us (1) to compare ML and AP responses evoked by RALP and LARP stimuli to existing literature showing those responses evoked by roll and pitch stimuli and (2) to characterize postural responses for individuals with sensory deficits to better isolate contributions of the vertical semicircular canals to postural control.

引言
本研究通过采用正弦和（sum-of-sines, SoS）或伪随机三元序列（pseudorandom ternary sequence, PRTS）生成运动平台的外部连续扰动，以量化内侧-外侧（medial-lateral, ML）或前-后（anterior-posterior, AP）方向诱发的身体晃动，最终助力阐明人类姿势控制系统的工作机制。以往此类扰动刺激多通过运动平台的俯仰（pitch）倾斜实现前-后方向平衡反应的评估，或通过滚转（roll）倾斜实现内侧-外侧方向平衡反应的评估。然而，目前尚不清楚健康的姿势控制系统在面对二维（2D）扰动时，当扰动刺激以半规管坐标系（即右前/左后（right-anterior/left-posterior, RALP）和左前/右后（left-anterior/right-posterior, LARP））呈现时，其反应是否与以俯仰/滚转坐标系呈现时一致。两类坐标系下的扰动刺激在时间与空间维度上均相互正交。本研究采用的RALP/LARP坐标系二维平台扰动，有望更好地评估垂直半规管功能障碍患者的双侧垂直半规管对姿势控制的贡献。

方法
为填补这一研究空白，本研究采用正弦和（SoS）信号生成了4种不同的平衡扰动轨迹，并同时在以下三类维度下施加扰动刺激：(i) 滚转（roll）与俯仰（pitch）维度；(ii) RALP与LARP维度；(iii) 滚转、俯仰、RALP及LARP维度。本研究通过商用运动平台（Virtualis Motion VR，法国Perault公司）采集了24名健康受试者的压力中心（center of pressure, CoP）数据，受试者年龄为13至40岁（原文此处疑似笔误，原句为“40 13 years of age”）。对压力中心数据进行离散傅里叶变换（discrete Fourier transform, DFT），以识别扰动频率下的反应（即频谱响应分量）。

结果
我们发现，当平台扰动同时以RALP/LARP坐标系与俯仰/滚转坐标系施加时，受试者的内侧-外侧与前-后方向姿势反应无显著差异。

讨论
本研究结果表明，采用RALP/LARP坐标系的二维平台扰动可实现两大研究目标：(1) 将RALP与LARP刺激诱发的内侧-外侧、前-后方向姿势反应，与已有文献中俯仰、滚转刺激诱发的同类反应进行对比；(2) 为存在感觉缺陷的个体表征姿势反应，从而更精准地分离垂直半规管对姿势控制的贡献。