investigating coordinate transform processes with electrical vestibular stimulation
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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. - PowerPoint PPT PresentationTRANSCRIPT
Investigating Coordinate Transform processes with Investigating Coordinate Transform processes with Electrical Vestibular StimulationElectrical Vestibular Stimulation
Raymond ReynoldsRaymond ReynoldsSports and Exercise SciencesSports and Exercise Sciences
College of Life and Environmental SciencesCollege of Life and Environmental Sciences
Coordinate transform process for balance
Same vestibular signal can requiredifferent balance response
For vestibular reflexes to be effective, must compute head-on-feet transform
Can use vestibular stimulation to investigate this process
How does GVS work?
Day & Fitzpatrick, J Phys 2005
Head roll around a naso-occiptial axis
Fitzpatrick et al, Current Biology 2006
Effect of GVS on walking trajectory
Effect of GVS on walking trajectory
• 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?
Vertical torque response during stance
Effect of Vestibular Stimulation Upon Vertical Torque
Response to Square Wave Stimuli
Small but significant torque and trunk yaw response
Affected by head position
Response to Stochastic Stimulation
SVS response smoothly modulated by head pitch.
Response to Stochastic Stimulation
CorrelationCoefficient
Time (ms)Head P
itch (d
egrees)
Variation with Head Pitch
Confirms mechanism of GVS:Naso-occiptial rotation
Can now assess changes in response bias & certainty
Bias Certainty
Are such changes associated with postural instability/fall risk?
Frequency domain reveals two responses
Two rotation vectors?Lateral response masquerading as a rotation?
Coh
eren
ce
Otolith and Canal responses to GVS
Cathers et al, J Phys 2005
Coupling between lateral sway and torque
Coupling only occurs for M-L sway, not A-PC
oher
ence
Biomechanical coupling due to body asymmetry in sagittal plane.
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:
1) Canal-mediated roll (dominant)2) Otolith-based linear acceleration.
Effect of High and Low Frequency stimulation
0-5Hz 5-10Hz
Yaw
Pitch
Roll