Postural demands modulate tactile perception in the lower limb in young and older adults
Balance control requires constant integration of feedforward and feedback signals. In healthy aging, the quality of feedback signals decreases while feedforward control is upweighted; but it is unclear how tactile perception is modulated when balance control is challenged and how this interacts with age-related changes in sensorimotor processes. We therefore examined tactile perception in standing when confronted with different postural demands in young and older adults. To this end, we measured tactile sensitivity on the calf during sitting (baseline), standing on solid ground, and standing on unstable ground (foam). We also measured the center of pressure during standing using a force plate and calculated a 95% confidence ellipse area and the center of pressure length. Tactile sensitivity was assessed by fitting a psychometric function to verbal responses for detecting vibrotactile probes, calculating the detection threshold at 50% detection, and normalizing the two standing conditions to baseline. We examined the effect of age and postural demands on the center of pressure kinematics and detection thresholds. We found higher sway and poorer tactile sensitivity when standing on foam irrespective of age. The increase of postural demands seems to reduce the reliance on tactile feedback signals from the lower limbs in both young and older adults. Our results suggest that postural demands challenge healthy agers as young adults, probably leading to a down-weighting of tactile feedback processing.