Plantar cutaneous afferents influence the perception of Subjective Visual Vertical in quiet stance

A Foisy,Z Kapoula

doi:10.1038/s41598-018-33268-3

Abstract

The estimation of Subjective Visual Vertical (SVV) involves the allocentric, gravitational and egocentric references, which are built by visual, vestibular and somatosensory afferents. Our goals were to assess the influence of plantar cutaneous afferents on the perception of SVV, and to see if there is a difference according to the efficiency of plantar cutaneous afferents. We recruited 48 young and healthy subjects and assessed their SVV and postural performances in quiet stance with a force platform, at 40 or 200 cm, in four ground conditions: on firm ground, on foam, with a bilateral, or with a unilateral 3 mm arch support. We also assessed the efficiency of our subjects’ plantar afferents with the plantar quotient method and divided them in two groups: subjects with a normal use of plantar afferents and subjects with Plantar Exteroceptive Inefficiency (PEI). The results showed significant decreases in the counter clockwise SVV deviation only with the unilateral arch support, at near distance, and among the typically behaving subjects. We conclude that asymmetric foot cutaneous afferents are able to bias the egocentric vertical reference and hence influence the perception of SVV. This influence disappears among subjects with PEI, probably because of a distortion of the plantar signal.

Highlights

Spatial representations require the integration of visual, vestibular and somatosensory cues, which takes place in various areas of the Central Nervous System (CNS)
Since plantar cutaneous afferents are normally used by the CNS to ensure postural control[45], a decrease of their use does not seem to correspond to a simple idiosyncrasy. We concluded that this minority of healthy people were unable to properly use their plantar cutaneous afferents both for balance and vergence control. We proposed that it corresponds to a situation revealing inefficiency in plantar cutaneous afferents (Plantar Exteroceptive Inefficiency - PEI)
Mann-Whitney U tests showed that subjects with PEI and typically behaving subjects did not have significantly different ages (z = 0.12, p = 0.90), heights (z = −0.03, p = 0.98), weights (z = 0.58, p = 0.65), stereoacuity (z = 0.90, p = 0.37), visual acuity (z = −0.22, p = 0.83), amplitude of accommodation (z = 1.83, p = 0.07) and Near Convergence Point (z = −0.81, p = 0.42)

Summary

Introduction

Spatial representations require the integration of visual, vestibular and somatosensory cues, which takes place in various areas of the Central Nervous System (CNS). The influence of somatosensory cues has been underscored by Anastasopoulos et al.[25], who showed that two patients with complete hemisensory loss were insensitive to the deviation of SVV estimate (opposite to the side of the body tilt, i.e. A-effect) when lying on the hypoesthetic side. These authors concluded that the A-effect is primarily somatosensory, not otolithic. Roll et al.[36] showed that vibrations applied to the foot soles of restrained and blindfolded subjects give rise to illusory perceptions of whole-body leaning This result suggests that foot cutaneous afferents contribute to the spatial representation of body posture. The specific influence of foot cutaneous afferents on the perception of verticality during quiet standing in healthy subjects has never been studied

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