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Investigating Coordinate Transform processes with Electrical Vestibular Stimulation

Investigating Coordinate Transform processes with Electrical Vestibular Stimulation Raymond Reynolds Sports and Exercise Sciences College of Life and Environmental Sciences. Coordinate transform process for balance. Same vestibular signal can require different balance response.

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Investigating Coordinate Transform processes with Electrical Vestibular Stimulation

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  1. Investigating Coordinate Transform processes with Electrical Vestibular Stimulation Raymond Reynolds Sports and Exercise Sciences College of Life and Environmental Sciences

  2. Coordinate transform process for balance Same vestibular signal can require different balance response For vestibular reflexes to be effective, must compute head-on-feet transform Can use vestibular stimulation to investigate this process

  3. How does GVS work? Head roll around a naso-occiptial axis Day & Fitzpatrick, J Phys 2005

  4. Effect of GVS on walking trajectory Fitzpatrick et al, Current Biology 2006

  5. Effect of GVS on walking trajectory

  6. Vertical torque response during stance • Can GVS induce vertical torque responses in standing subjects? • Can this be used to assess neck proprioception in pitch? • Causal link between aberrant transform processes and postural instability?

  7. Effect of Vestibular Stimulation Upon Vertical Torque

  8. Response to Square Wave Stimuli Small but significant torque and trunk yaw response Affected by head position

  9. Response to Stochastic Stimulation SVS response smoothly modulated by head pitch.

  10. Response to Stochastic Stimulation Correlation Coefficient Head Pitch (degrees) Time (ms)

  11. Variation with Head Pitch Confirms mechanism of GVS: Naso-occiptial rotation

  12. Can now assess changes in response bias & certainty Bias Certainty Are such changes associated with postural instability/fall risk?

  13. Frequency domain reveals two responses Coherence Two rotation vectors? Lateral response masquerading as a rotation?

  14. Otolith and Canal responses to GVS Cathers et al, J Phys 2005

  15. Coupling between lateral sway and torque

  16. Coupling only occurs for M-L sway, not A-P Coherence Biomechanical coupling due to body asymmetry in sagittal plane.

  17. Summary • Vestibular stimulation induces vertical torque responses when standing. • Provides a new tool to examine links between aberrant coordinate-transform processes and postural instability. • Coupling between M-L sway and vertical torque at high frequency. • Modulation with head position confirms the dual-action mechanism of GVS: • Canal-mediated roll (dominant) • Otolith-based linear acceleration.

  18. Effect of High and Low Frequency stimulation 0-5Hz 5-10Hz Yaw Pitch Roll

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