Electrical Vestibular Stimuli to Enhance Vestibulo-Motor Output and Improve Subject Comfort

Abstract

Electrical vestibular stimulation is often used to assess vestibulo-motor and postural responses in both clinical and research settings. Stochastic vestibular stimulation (SVS) is a recently established technique with many advantages over its square-wave counterpart; however, the evoked muscle responses remain relatively small. Although the vestibular-evoked responses can be enhanced by increasing the stimulus amplitude, subjects often perceive these higher intensity electrical stimuli as noxious or painful. Here, we developed multisine vestibular stimulation (MVS) signals that include precise frequency contributions to increase signal-to-noise ratios (SNR) of stimulus-evoked muscle and motor responses. Subjects were exposed to three different MVS stimuli to establish that: 1) MVS signals evoke equivalent vestibulo-motor responses compared to SVS while improving subject comfort and reducing experimentation time, 2) stimulus-evoked vestibulo-motor responses are reliably estimated as a linear system and 3) specific components of the cumulant density time domain vestibulo-motor responses can be targeted by controlling the frequency content of the input stimulus. Our results revealed that in comparison to SVS, MVS signals increased the SNR 3–6 times, reduced the minimum experimentation time by 85% and improved subjective measures of comfort by 20–80%. Vestibulo-motor responses measured using both EMG and force were not substantially affected by nonlinear distortions. In addition, by limiting the contribution of high frequencies within the MVS input stimulus, the magnitude of the medium latency time domain motor output response was increased by 58%. These results demonstrate that MVS stimuli can be designed to target and enhance vestibulo-motor output responses while simultaneously improving subject comfort, which should prove beneficial for both research and clinical applications.

Stabilization demands of walking modulate the vestibular contributions to gait

“…To examine the vestibulo-motor coupling between the input stimulus (i.e. EVS) and motor output (EMG and ground reaction forces) across our conditions, we computed the time-frequency coherence and gain assuming a linear stimulus-response relationship 56 . This analysis was performed based on continuous Morlet wavelet decomposition 12,57 using equations (1) and (2): where Pxy(τ, f) ( τ and f denote the stride time and frequency, respectively) is the time-dependent cross-spectrum between the EVS and rectified EMG or GRF, and Pxx(τ, f) and Pyy(τ, f) are the time-dependent auto-spectra of the EVS and rectified EMG or GRF, respectively.…”

Electrical Vestibular Stimuli Evoke Robust Muscle Activity in Deep and Superficial Neck Muscles in Humans

“…In turn, cross-correlation between the stimulus and muscle activity is equivalent to responses evoked by square-wave stimuli ( 8 , 20 ). Furthermore, stochastic stimuli offer several experimental advantages, including increased signal-to-noise ratios ( 21 , 22 ), minimized anticipation to the stimulus ( 23 ), reduced experimental durations ( 20 ), and less irritation or nausea evoked by the stimulus ( 20 ).…”

Quantifying Nonlinear Contributions to Cortical Responses Evoked by Continuous Wrist Manipulation

“…Mechanical (i.e. joint angle and torque) and EMG recordings obtained from continuous mechanical TNSRE-2015-00235 stimulation also show a small response at non-stimulated frequencies [18][19][20]. Nonlinear responses in the sensorimotor system could result from sensors (e.g.…”