Reduced postural sway during quiet standing by light touch is due to finger tactile feedback but not mechanical support |
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Authors: | Motoki Kouzaki Kei Masani |
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Institution: | (1) Laboratory of Neurophysiology, Graduate School of Human and Environmental Studies, Kyoto University, Yoshida-nihonmatsu, Sakyo-ku, Kyoto 606-8501, Japan;(2) Rehabilitation Engineering Laboratory, Institute of Biomaterials and Biomedical Engineering, University of Toronto, Toronto, ON, Canada;(3) Rehabilitation Engineering Laboratory, Lyndhurst Centre, Toronto Rehab, Toronto, ON, Canada |
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Abstract: | It is well known that a light and voluntary touch with a fingertip on a fixed surface improves postural stability during quiet
standing. To determine whether the effect of the light touch is due to the tactile sensory input, as opposed to mechanical
support, we investigated the light touch effect on postural stability during quiet standing with and without somatosensory
input from the fingertip. Seven young subjects maintained quiet standing on a force platform with (LT) and without (NT) lightly
touching a fixed surface, and with (TIS) and without (CON) the application of tourniquet ischemia, which removed the tactile
sensation from the fingertip. The mean velocity of centre of pressure (CoP) was calculated to assess the postural sway in
each condition. The mean velocity of CoP was significantly smaller in the LT condition compared to the NT condition only under
the CON condition, whereas the light touch effect was not significant under the TIS condition. We found that the reduction
of the horizontal ground reaction force due to the light touch was about 20%, which was approximately equivalent to the reduction
of mean velocity of CoP in the LT condition compared to the NT condition. Since the fingertip contact force was relatively
large compared to the horizontal ground reaction force, one could say that the light touch effect might be due to the mechanical
support provided by the contact itself. However, we demonstrated experimentally that light touch effects were diminished due
to loss of finger tactile feedback induced by the tourniquet ischemia, but not due to the mechanical support provided by the
light touch. One possible reason is the lack of feedback information in controlling posture, and the other is the altered
control of the arm induced by the loss of tactile feedback. |
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Keywords: | Posture Fingertip Centre of pressure Tourniquet ischemia |
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