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Marc Monsour, Tanya D. Ivanova, Tim D. Wilson and S. Jayne Garland

The purpose of this study was to investigate whether application of bipolar galvanic vestibular stimulation (GVS) would influence the common modulation of motor unit discharge rate in bilateral soleus muscles during quiet standing. Soleus motor unit activity was recorded with fine wire electrodes in each leg. Subjects stood, with eyes closed, on two adjacent force platforms to record postural sway with the head facing straight ahead, turned to right, or turned left. Subjects also swayed voluntarily without GVS to the same position as evoked during the GVS. There was no difference in the common drive to bilateral soleus motoneurons during quiet standing and voluntary sway tasks. Common drive was significantly lower during right cathode GVS with the head straight or turned to the right. These results demonstrate that manipulation of vestibular afferent input influences the common modulation of bilateral soleus motor unit pairs during quiet standing.

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Kai Yan Lui, Patricia Hewston and Nandini Deshpande

(Optometry Laboratory, University of Waterloo, Waterloo, ON) to simulate the effects of dense cataracts ( Deshpande & Patla, 2007 ). Vestibular input was manipulated using percutaneous bipolar galvanic vestibular stimulation (GVS; Grass S48 Square Pulse Stimulator; Grass Technologies, Subsidiary of AstroNova

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Kristen E. Thomas and Leah R. Bent

The integration of vestibular and somatosensory information for the control of lower limb musculature remains elusive. To determine whether a subthreshold vestibular input influences the cutaneous evoked response, the isometric EMG activity in the posturally inactive soleus muscles of 13 healthy, seated subjects was collected. Vestibular afferents were activated using galvanic vestibular stimulation (GVS; 1.8–2.5mA, 500ms), while percutaneous electrical stimulation was delivered to the distal tibial nerve (11ms train of 3 × 1.0 ms pulses, 200Hz) to activate foot sole skin afferents. GVS elicited responses in soleus both independently and when combined with cutaneous stimulation. The responses to the combined sensory input showed an interaction between the two sensory modalities to influence muscle activation. Of note is the presence of significant muscle modulation in the combined condition, where subthreshold vestibular inputs altered the outcome of the cutaneous reflex response. This finding has implications for individuals with sensory deficiency. In the case of an absent or deficient sensory modality, balance protective reflexes to maintain postural equilibrium may be enhanced with targeted sensory augmentation.

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Fang Zhang and Nandini Deshpande

Fifteen young (20–30 years old) and 15 older (>65 years old) healthy participants were recruited to investigate age-related differences in head and trunk control under suboptimal vestibular conditions (galvanic vestibular stimulation, or GVS) and vision conditions during normal and narrow-based walking. Head-roll velocity decreased in the blurred-vision condition and marginally increased with GVS in older but not in young participants. Head pitch increased, whereas head-roll velocity decreased in narrow-base walking. Trunk pitch, trunk-pitch velocity, and gait speed increased with GVS, whereas trunk-pitch velocity and gait speed decreased in narrow-base walking. Marginally increased head-roll velocity in the older participants possibly suggests decreased integrative ability of the central nervous system in elderly people. The changes in head control during narrow-base walking may be an attempt to simplify the interpretation of the vestibular signal and increase otolith sensitivity. The complexity of controlling the trunk in the mediolateral direction was suggested by different strategies used for trunk control in different conditions.

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Hendrik Reimann, Tyler Fettrow and John J. Jeka

 al. ( 2017 ). They applied galvanic vestibular stimulation during gait initiation to perturb the sensory system and induce the sensation of falling to one side ( Bent, McFadyen, Merkley, Kennedy, & Inglis, 2000 ). In response to this stimulus, the subjects’ CoP under the stance foot shifted laterally in the

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Andressa Busch Rocha Pereira and Renato Moraes

.L. , & Fitzpatrick , R.C. ( 2003 ). Position and velocity responses to galvanic vestibular stimulation in human subjects during standing . Journal of Physiology, 547 , 293 – 299 . PubMed doi:10.1113/jphysiol.2002.030767 10.1113/jphysiol.2002.030767 Wickremaratchi , M.M. , & Llewelyn , J.G. ( 2006