. We investigated age-related changes in adaptation and sensory reintegration in postural control without vision. In two sessions, participants adapted their posture to sway reference and to reverse sway reference conditions, the former reducing (near eliminating) and the latter enhancing (near doubling) proprioceptive information for posture by means of support-surface rotations in proportion to body sway. Participants stood on a stable platform for 3 min (baseline) followed by 18 min of sway reference or reverse sway reference (adaptation) and finally again on a stable platform for 3 min (reintegration). Results showed that when inaccurate proprioception was introduced, anterior-posterior (AP) sway path length increased in comparable levels in the two age groups. During adaptation, young and older adults reduced postural sway at the same rate. On restoration of the stable platform in the reintegration phase, a sizeable aftereffect of increased AP path length was observed in both groups, which was greater in magnitude and duration for older adults. In line with linear feedback models of postural control, spectral analyses showed that this aftereffect differed between the two platform conditions. In the sway-referenced condition, a switch from lowto high-frequency COP sway marked the transition from reduced to normal proprioceptive information. The opposite switch was observed in the reverse sway referenced condition. Our findings illustrate age-related slowing in participants' postural control adjustments to sudden changes in environmental conditions. Over and above differences in postural control, our results implicate sensory reweighting as a specific mechanism highly sensitive to age-related decline.
I N T R O D U C T I O NControl of upright standing relies on the integration of sensory signals from vestibular, visual, and proprioceptive channels, thereby capitalizing on the redundancy of sensory information in this task (for a review, see Balasubramaniam and Wing 2002). This plethora of available information allows humans to maintain postural stability even when information from one or even two of the sensory channels is compromised, for instance, in age-or disease-related loss of vestibular, visual, or proprioceptive function, by reweighting information from the remaining channels. In daily living, the ability to quickly reweight sensory information in response to sudden changes in the environment is also frequently challenged, for example, when a bus is stopping or when moving from a bright to a dark environment. Although such adaptations have been identified as one of the contributing factors to fall accidents in older adults (Horak 2006), empirical evidence related to changes in the speed and nature of sensory integration in the elderly is surprisingly sparse. In this study, we investigate how young and older adults adapt their postural control when inaccurate proprioceptive information is introduced. Our focus is on age differences in the time course of adaptation and on the nature of underlying senso...