This week’s post is an excerpt from my book: Vestibular Function: Clinical and Practice Management (Thieme 2011).
“The primary role of the balance system is to allow humans to interact and maintain contact with their surroundings in a safe, efficient manner. As humans move through their environment, information is gathered through their visual, somatosensory, and vestibular senses and sent to the brain stem for integration and finally to the cortex for perception and processing . The visual and somatosensory reference information is constantly changing as a function of movement, but the vestibular reference––gravity––is unchanging. As long as the information arriving from these three sources is predictable and non-conflicting, equilibrium is maintained and there is little thought regarding balance.
When a sensory conflict occurs, the brain must efficiently and quickly (reflexively) adjust the level of priority given to the conflicting incoming information, or a sensation of imbalance may occur. Because the known constant in the mix is gravity, humans tend to rely more on vestibular information for maintenance of dynamic balance than they do on proprioceptive or visual information (when the peripheral vestibular system is damaged, this may change).
Allum and Pfaltz (1985) {{1}}[[1]]Allum, H. J., & Pfaltz, C. R. (1985). Visual and vestibular contributions to pitch sway stabilization in the ankle muscles of normals and patients with bilateral peripheral vestibular deficits. Exp Brain Res, 58, 82–94[[1]] hypothesized that vestibular information contributes 65% to dynamic body stability; vision and proprioception providing less of a contribution. Standing balance, however, does not rely primarily on vestibular information. Colledge et al. (1994){{2}}[[2]]Colledge, N. R., Cantley, P., Peaston, I., Brash, H., Lewis, S., & Wilson, J. A. (1994). Ageing and balance: The measurement of spontaneous sway by posturography. Gerontology, 40, 273–278.[[2]] and Hobeika (1999){{3}}[[3]]Hobeika, C. P. (1999). Equilibrium and balance in the elderly. Ear Nose Throat J, 78(8), 558–566.[[3]] report that proprioception is the major contributor to standing balance; however, when proprioceptive input is not helpful (i.e., moving or compliant surface), vision becomes the primary source of information.
In summary, the balance system is dynamic and quickly responds to changes in visual, vestibular, and proprioceptive feedback. Although the peripheral vestibular system is most often of primary importance, the interactions between the peripheral vestibular inputs, vision, and proprioception in the brain are crucial to the maintenance of balance.”
