Time-course investigation of postural sway variability: Does anxiety exacerbate the sensory reweighting impairment in chronic stroke survivors?

Although anxiety is one of the most prevalent psychological disorders in stroke survivors, its effect on sensory reweighting has not yet been fully studied. The aim of this work was to investigate how anticipation of collision avoidance events affects sensory reweighting in chronic stroke survivors with low and high levels of anxiety (LA-stroke and HA-stroke, respectively), as compared with healthy controls (HC), under the condition of perturbed proprioception. Eighteen LA-stroke and 18 HA-stroke survivors, as well as 18 gender- and age-matched HC, participated in this study. Postural sway variability (i.e. Root Mean Square (RMS) of the COP velocity) was measured for a duration of 180 s under two conditions: quiet standing and standing while predicting random virtual spheres to be avoided. Proprioceptive perturbation was simulated using bilateral Achilles tendon vibration at mid duration (60 s) for both conditions. The results showed that the HC were able to timely use visual anticipation to reduce the postural sway variability induced by tendon vibration. However, marked delay in using such anticipation was observed in stroke participants, especially in the HA-stroke group, as indicated by a significant decrease in the RMS of the COP velocity late in the vibration phase. This is the first study to consider the effect of anxiety while comparing sensory reweighting between stroke and healthy participants. The results indicated that chronic stroke survivors, particularly those with HA, could not efficiently use sensory reweighting to maintain balance in sensory conflicting conditions, which may subject them to loosing balance and/or falling. These findings are critical for future assessment and planning of rehabilitation interventions and balance in chronic stroke survivors.