Decomposing sensorimotor variability changes in ageing and their connection to falls in older people

Chin-Hsuan Lin,A Aldo Faisal

doi:10.1038/s41598-018-32648-z

Abstract

The relationship between sensorimotor variability and falls in older people has not been well investigated. We developed a novel task having shared biomechanics of obstacle negotiation to quantify sensorimotor variability related to locomotion across age. We found that sensorimotor variability in foot placement increases continuously with age. We then applied sensory psychophysics to pinpoint the visual and somatosensory systems associated with sensorimotor variability. We showed increased sensory variability, specifically increased proprioceptive variability, the vital cause of more variable foot placement in older people (greater than 65 years). Notably, older participants relied more on the vision to judge their own foot’s height compared to the young, suggesting a shift in multisensory integration strategy to compensate for degenerated proprioception. We further modelled the probability of tripping-over based on the relationship between sensorimotor variability and age and found a correspondence between model prediction and community-based data. We reveal increased sensorimotor variability, modulated by sensation precision, a potentially vital mechanism of raised tripping-over and thus fall events in older people. Analysis of sensorimotor variability and its specific components may have the utility of fall risk and rehabilitation target evaluation.

Highlights

Falls are the leading cause of unintentional injuries in older people[1,2]; they account for more than 60% unintentional injuries and 50% of accidental death among people aged 65 and older[1]
We used standard deviations to represent the sensorimotor variability of the FOot HEight POsitioning (FOHEPO) task because Kolmogorov-Smirnov Goodness-of-Fit tests confirmed the normality of the foot height distributions (Supplementary Material Fig. 1)
We demonstrate a link between sensorimotor variability and minimum foot clearance (MFC) variability increases in older people

Summary

Introduction

Falls are the leading cause of unintentional injuries in older people[1,2]; they account for more than 60% unintentional injuries and 50% of accidental death among people aged 65 and older[1]. The neural signals, from sensation, motor planning to execution, are intrinsically noisy[11,14] This noise in the sensory and motor systems causes variations of motor performance across multiple repetitions of a task, i.e. sensorimotor variability[13,14,15]. Most studies probing the ageing effects on sensorimotor tasks have focused on the upper limb and consistently found higher sensorimotor variability in older people[16,17,18,19]. This increase of sensorimotor variability is associated with a deficiency in older people’s activities of daily living[16,20]. As modality specific measurements can lead to a more precise understanding of mechanisms behind increased sensorimotor and gait variability and the development of targeted fall prevention strategies, it is valuable to evaluate visual and proprioceptive variability separately

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