Putting proprioception for balance to the test: Contrasting and combining sway referencing and tendon vibration

Background: Postural control relies on sensory information from visual, vestibular and proprioceptive channels, with proprioception being the key sensory modality in this task. Two well-established ways of manipulating pro- prioceptive information in postural control are tendon vibration and sway referencing. The aim of the present study was to assess postural adaptation when inaccurate proprioceptive information is introduced using tendon vibration and sway referencing in isolation and combination.

Methods: Seventeen young adults were asked to stand, without vision, for 2 min on a fixed surface (baseline) im- mediately followed by 3 min of bilateral Achilles tendon vibration, sway reference, or combined presentation of the two manipulations (adaptation) and finally 3 min of standing on a fixed surface (aftereffect).

Results: During adaptation, vibration showed the lowest sway variability, followed by sway reference and the combined condition. Spectral analyses focusing on the dominant frequencies in this task (0–0.4 Hz) showed that in the first half of adaptation sway amplitude was greater when the two manipulations were combined com- pared with each manipulation alone. However, in the second half differences between sway reference and the combined condition disappeared but differences between vibration and the other two conditions increased.

Conclusion: We interpret these findings primarily as due to a prolonged attenuation in effects of vibration over the course of the adaptation phase and we offer two explanations for this phenomenon. One is a decline in neu- rotransmitter release from the group Ia terminals and the other is sensory reweighting which down-weights pro- prioception and up-weights the accurate, vestibular information.