The effect of proprioceptive acuity variability on motor adaptation in older adults.

Motor adaptation requires efficient integration of sensory information with predicted sensory consequences of one's own action. However, the effect of reduced sensory acuity on motor adaptation in humans remains to be further investigated. Here, we examined the variability of proprioceptive acuity during an arm-position matching task and the pattern of visuomotor adaptation in older and young adults, and determined the relationship between the two variables. The older adults, a known example of impaired proprioceptive acuity, exhibited greater trial-to-trial variability during the arm-position matching task as compared with the young adults. Furthermore, the older adults showed a slower rate of adaptation to a 30° visuomotor rotation during targeted reaching movements, as well as larger movement errors in the later phase of adaptation, than the young adults. Our correlation analyses indicated a negative association between the variability in proprioceptive acuity and the rate of visuomotor adaptation in the older adults; and no association was observed in the young adults. These findings point to a possibility that an increase in the variability of proprioceptive acuity due to aging may weaken the integration of predicted and actual sensory feedback, which in turn may result in poor visuomotor adaptation in older adults.