Passive tactile sensory input improves stability during standing

The effects of passive tactile cues about body sway on stability during sta nding were evaluated in subjects with a wide range of sensorimotor and bala nce performance. Healthy young adults, diabetic subjects with varying degre es of peripheral sensory neuropathy and older subjects aged 70-80 years wer e 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 sk in at the leg or shoulder as the body swayed. The results show that this st imulus reduced body sway (mean reduction 24.8%+/-1.5) and thus had a stabil izing effect as big as vision or sensory information from the feet. The red uction in sway was not based on active touch. The stimulus was not restrict ed to a particular region of the body, but was more effective on the should er than the leg, and was more effective when standing with eyes shut or whe n standing on the foam mat. It was also most effective in those subjects wh o had the greatest sway during normal standing. Thus, the response appears to be graded with the amplitude of the stimulus. We concluded that, if pass ive sensory input about posture is available, the postural control process adapts to this input, modulating postural stabilizing reactions.