Effect of visual field motion on vestibulo-myogenic response during upright stance: A pilot study
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1
Temple University, Physical Therapy, United States
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2
Shriners Hospitals for Children - Philadelphia, United States
BACKGROUND
Maintaining upright stance requires the continuous update on sensory information from the primary systems in order to estimate the current state of postural orientation (Peterka, 2002). While each sensory system is responsible for unveiling a specific aspect of body motion, changes in one sensory system can also alter sensory input from another sensory system. This process of adjusting sensory contributions to balance control is referred to as sensory reweighting (Asslander & Peterka, 2014). Sensory reweighting would explain why the magnitude of the postural response due to galvanic vestibular stimulation (GVS) is dependent upon non-vestibular sensory signals (Fitzpatrick & Day, 2004). A much greater postural response can be elicited by GVS, when visual information is made unavailable (Welgampola & Colebatch, 2001). Individuals standing quietly in an immersive virtual environment where the visual surround is continuously moving exhibit postural sway in the direction of the visual flow (Wang, Kenyon, & Keshner, 2010). Thus, vestibular reafference could be modulated by visual flow as it is by fear of falling (Naranjo, Allum, Inglis, & Carpenter, 2015) and weakened muscle strength around the ankle (McIntosh, Power, & Dalton, 2018). The purpose of the current study was to explore whether vestibular reafference would be modulated by visual field motion. Results of this study provide a physiological interpretation for changes in the postural response due to visual field motion.
METHODS
Subjects: Eight healthy young adults (8 females; 28.0 ± 6.0 years) with no history of neurological disorder gave informed consent to participate in the current study. All subjects had no known history of vestibular or hearing deficit. All participants had a minimum of 20/40 corrected vision. The experimental protocol was approved by the Temple University Ethics Board. Using the Rod-and-Frame test, all participants were identified as visually independent (Yu, Lauer, Tucker, Thompson, & Keshner, 2018).
Virtual Environment: The immersive virtual environment consisted of three screens facing the front, right, and left of the subject. The overall dimension of the virtual environment was 3.5m (width), 3.5m (depth), and 6.1m (height). One Panasonic PT-DX610 DLP-based projectors positioned behind each screen projected a full-color field with the resolution of 1024x768 pixels at a 60 Hz refresh rate. The image of the virtual environment was created in Unity (Unity Technologies SF, San Francisco, CA, USA).
Vestibular Evoked Myogenic Potential (VEMP): Acoustic air-conducted stimulation consisting of 500Hz, 125dB SPL tone bursts, with 1ms rise/fall time, 2ms plateau, at a repetition rate of 5 Hz, was delivered monaurally though in-ear earphones (ER-3C, Etymotic Research Inc., Elk Grove Village, IL, USA). The electromyogram (EMG) signals representing cervical vestibular evoked myogenic potential (cVEMP) responses were recorded with disposable, self-adhesive, pre-gelled, Ag/AgCl electrodes with 40-inch safety leadwires (GN Otometrics, Schaumbaurg, IL, USA), which were amplified (2500x) and band-pass filtered (20 – 2000Hz) for cVEMPs. A non-inverting electrode was placed at the mid-point of the sternocleidomastoid (SCM) muscle on each side. An inverting electrode was placed at the sternoclavicular junction on each side. A ground electrode was placed on the manubrium sterni.
Procedure: Participants were instructed to perform quiet stance in the center of the virtual environment. For left cVEMP testing, for example, participants were asked to look over the right shoulder to face the front screen with their body parallel to the left screen and actively contract the left SCM throughout the trial. During each 20-second trial, the visual field motion was kept either stationary (EO) or continuously rolling about the nasion-to-inion axis (RU) at 30°/s. Additionally, the acoustic air-conducted stimulation (100 tone-bursts) was delivered over the 20-second period. Three trials were performed for each condition on each side.
Response parameters: The cVEMP waveform consists of a positive peak (p13), identified as the first distinctive valley in the waveform that appears 11ms – 16ms post tone burst, and a negative peak (n23), identified as the first distinctive peak in the waveform that appears 18ms – 26ms post tone burst. Mean values for cVEMP latencies and amplitudes were calculated separately for p13 and n23; peak-to-peak (p13-n23) amplitudes were also calculated. Muscle background activity of each SCM was calculated using the area under the curve of the rectified EMG over the 10ms window pre-stimulus.
Statistical Analysis: Paired-sample t-tests were used to compare differences between EO and RU conditions for all dependent measures with the level of statistical significance set at p = 0.05.
RESULTS
A significant effect of visual field motion emerged in cVEMP amplitudes (p=.014). Specifically, the p13 amplitudes were significantly reduced by the RU visual scene condition (Figure 1; EO: 21.1±4.2 uV; RU: 17.7±3.7 uV). No significant differences between the stationary and roll visual conditions were found in n23 amplitudes, p13 and n23 latencies, and p13-n23 peak-to-peak amplitudes or in the background EMG activity (ps>.05).
DISCUSSION
Changes in the magnitude of the cVEMP suggest that vestibular reafference was modulated by visual field motion in the virtual environment even though all of the healthy participants in this study were identified as visually independent. To our knowledge, this is the first study to elicit and record VEMPs during upright stance with different conditions of visual field motion. These results provide a foundation for future studies examining vestibulo-myogenic responses in individuals with visual dependence due to neurological disorders (e.g., stroke, cerebral palsy). Comparison of vestibulomyogenic responses as a function of illusion of self-motion due to visual field motion (or vection) could further explain how the nervous system weights these signals in the natural environment.
Acknowledgements
This work is supported by the Shriners Hospitals for Children Postdoctoral Fellowship (#84308-PHI) to Yawen Yu.
References
Asslander, L., & Peterka, R. J. (2014). Sensory reweighting dynamics in human postural control. J Neurophysiol, 111(9), 1852-1864. doi: 10.1152/jn.00669.2013
Fitzpatrick, R., & Day, B. (2004). Probing the human vestibular system with galvanic stimulation. Journal of Applied Physiology, 96, 2301-2316. doi: 10.1152/japplphysiol.00008.2004.
McIntosh, E. I., Power, G. A., & Dalton, B. H. (2018). The vestibulomyogenic balance response is elevated following high-intensity lengthening contractions of the lower limb. Neurosci Lett. doi: 10.1016/j.neulet.2018.03.056
Naranjo, E. N., Allum, J. H., Inglis, J. T., & Carpenter, M. G. (2015). Increased gain of vestibulospinal potentials evoked in neck and leg muscles when standing under height-induced postural threat. Neuroscience, 293, 45-54. doi: 10.1016/j.neuroscience.2015.02.026
Peterka, R. J. (2002). Sensorimotor integration in human postural control. J Neurophysiol, 88(3), 1097-1118.
Wang, Y., Kenyon, R. V., & Keshner, E. A. (2010). Identifying the control of physically and perceptually evoked sway responses with coincident visual scene velocities and tilt of the base of support. Exp Brain Res, 201(4), 663-672. doi: 10.1007/s00221-009-2082-0
Welgampola, M. S., & Colebatch, J. G. (2001). Vestibulospinal reflexes: quantitative effects of sensory feedback and postural task. Exp Brain Res, 139(3), 345-353.
Yu, Y., Lauer, R. T., Tucker, C. A., Thompson, E. D., & Keshner, E. A. (2018). Visual dependence modifies postural sway responses to continuous visual field motion in individuals with cerebral palsy. Dev Neurorehabil. doi: 10.1080/17518423.2018.1424265
Keywords:
virtual environment,
posture and balance,
sensorimotor integration,
Vestibular evoked myogenic potential (VEMP),
Vection
Conference:
2nd International Neuroergonomics Conference, Philadelphia, PA, United States, 27 Jun - 29 Jun, 2018.
Presentation Type:
Oral Presentation
Topic:
Neuroergonomics
Citation:
Yu
Y and
Keshner
EA
(2019). Effect of visual field motion on vestibulo-myogenic response during upright stance: A pilot study.
Conference Abstract:
2nd International Neuroergonomics Conference.
doi: 10.3389/conf.fnhum.2018.227.00086
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Received:
03 Apr 2018;
Published Online:
27 Sep 2019.
*
Correspondence:
PhD. Yawen Yu, Temple University, Physical Therapy, Philadelphia, PA, United States, yawen.yu@colostate.edu