Passive tactile sensory input improves stability during standing.

The effects of passive tactile cues about body sway on stability during standing were evaluated in subjects with a wide range of sensorimotor and balance performance. Healthy young adults, diabetic subjects with varying degrees of peripheral sensory neuropathy and older subjects aged 70-80 years were studied. Body sway was measured when subjects stood on the floor and on a foam rubber mat, with or without an applied stimulus that rubbed on the skin at the leg or shoulder as the body swayed. The results show that this stimulus reduced body sway (mean reduction 24.8%+/-1.5) and thus had a stabilizing effect as big as vision or sensory information from the feet. The reduction in sway was not based on active touch. The stimulus was not restricted to a particular region of the body, but was more effective on the shoulder than the leg, and was more effective when standing with eyes shut or when standing on the foam mat. It was also most effective in those subjects who had the greatest sway during normal standing. Thus, the response appears to be graded with the amplitude of the stimulus. We concluded that, if passive sensory input about posture is available, the postural control process adapts to this input, modulating postural stabilizing reactions.

Effects of galvanic vestibular stimulation during human walking.

1. To identify vestibular influences on human walking, galvanic vestibular stimulation was applied to normal adult subjects as they walked to a previously seen target. A transmastoidal step stimulus commenced as subjects started walking. With the eyes shut, the galvanic stimulus caused large turns towards the side with the anodal current. 2. Ability to perceive the trajectory of gait without visual cues was measured by guiding blindfolded subjects from one arbitrary point to another, either walking or seated in a wheelchair. On reaching a destination position and removing the blindfold, subjects pointed to indicate the starting position. Subjects made considerable errors in estimating the trajectory, but were equally accurate whether in the wheelchair or walking. 3. To determine the effects of vestibular stimulation on the perception of trajectory, the galvanic stimulus was applied to blindfolded subjects as they were guided from one point to another in the wheelchair. The vestibular stimulus produced an illusory shift in the trajectory travelled. This shift was towards the side with the cathode, i.e. in the opposite direction to the turn produced by the stimulus during walking. 4. We conclude that galvanic vestibular stimulation during walking causes subjects to turn from their planned trajectory. In part, this altered course may compensate for an altered perception of trajectory produced by the stimulus. However, altered perception of the vertical or the base of support, or direct vestibulo-fugal influences on the leg muscles could contribute to the changes in gait.