Vertical torque responses to vestibular stimulation in standing humans

Area of Science:

• Neuroscience
• Biomechanics
• Human Movement Science

Background:

• Electrical vestibular stimulation (EVS) can evoke sensations of head roll and inter-aural linear acceleration.
• These sensations influence postural control, particularly during locomotion.
• The specific generation of vertical torque (T(z)) during stance in response to EVS requires further investigation.

Purpose of the Study:

• To investigate the effects of EVS on vertical torque (T(z)) generation during quiet standing.
• To differentiate between torque responses related to head roll sensation and other potential mechanisms.
• To explore the influence of head pitch and orientation on EVS-evoked torque responses.

Main Methods:

• Subjects performed quiet stance with varying head pitches.
• Square-wave and stochastic vestibular stimulation (SVS) were applied to the mastoid processes.
• Vertical torque (T(z)), trunk yaw, and coherence at specific frequencies were measured.
• The effect of head roll and yaw on high-frequency responses was assessed.

Main Results:

• EVS evoked a polarity-specific T(z) response and trunk yaw with the head tilted forward.
• SVS revealed a low-frequency (2–3 Hz) T(z) response modulated by head pitch, consistent with head roll sensation.
• A separate high-frequency (7–8 Hz) T(z) response was unaffected by head pitch but attenuated by head roll/yaw, suggesting mechanical coupling to medio-lateral sway.

Conclusions:

• Two distinct vertical torque responses to EVS were identified in standing subjects.
• The low-frequency response is linked to the sensation of head roll, offering a new way to study vestibular-proprioceptive interactions.
• The high-frequency response is attributed to mechanical coupling with EVS-induced medio-lateral body sway.