Electro-tactile stimulation of the posterior neck induces body anteropulsion during upright stance

A M De Nunzio,D Farina,D Falla,U S Yavuz,E Martinez-Valdes

doi:10.1007/s00221-018-5229-z

A M De Nunzio, D Farina + Show 3 more

Open Access

https://doi.org/10.1007/s00221-018-5229-z

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Abstract

Sensory information conveyed along afferent fibers from muscle and joint proprioceptors play an important role in the control of posture and gait in humans. In particular, proprioceptive information from the neck is fundamental in supplying the central nervous system with information about the orientation and movement of the head relative to the rest of the body. The previous studies have confirmed that proprioceptive afferences originating from the neck region, evoked via muscle vibration, lead to strong body-orienting effects during static conditions (e.g., leaning of the body forwards or backwards, depending on location of vibration). However, it is not yet certain in humans, whether the somatosensory receptors located in the deep skin (cutaneous mechanoreceptors) have a substantive contribution to postural control, as vibratory stimulation encompasses the receptive field of all the somatosensory receptors from the skin to the muscles. The aim of this study was to investigate the postural effect of cutaneous mechanoreceptor afferences using electro-tactile stimulation applied to the neck. Ten healthy volunteers (8M, 2F) were evaluated. The average position of their centre of foot pressure (CoP) was acquired before, during, and after a subtle electro-tactile stimulation over their posterior neck (mean ± SD = 5.1 ± 2.3 mA at 100 Hz—140% of the perception threshold) during upright stance with their eyes closed. The electro-tactile stimulation led to a body-orienting effect with the subjects consistently leaning forward. An average shift of the CoP of 12.1 ± 11.9 mm (mean ± SD) was reported, which significantly (p < 0.05) differed from its average position under a control condition (no stimulation). These results indicate that cutaneous mechanoreceptive inflow from the neck is integrated to control stance. The findings are relevant for the exploitation of electro-tactile stimulation for rehabilitation interventions where induced anteropulsion of the body is desired.

Highlights

Postural control is a skilled motor task based on processed activity of multimodal input integration (Maurer et al 2006; Chiba et al 2016) with the final aims of controlling the position of the center of body mass (CoM) allowing its ground projection to always fall inside the base of support (Winter et al 2003) and keeping the desired posture based on the appropriate alignment of body segments relative to vertical (Kristjansson and Treleaven 2009)
While a strong postural effect occurred along the A-P axis, the stimulation did not induce an increased oscillation or net movement of the centre of foot pressure (CoP) along the M-L axis
The results obtained in this study provide useful indications for the development of innovative assistive devices based on surface electro-tactile stimulation to prevent falls in elderly people, people with sensory-motor impairment, or balance disorders (Melzer et al 2004; Stolze et al 2005; Cozart and Cesario 2009; Delval et al 2014)

Summary

Introduction

Postural control is a skilled motor task based on processed activity of multimodal input integration (Maurer et al 2006; Chiba et al 2016) with the final aims of controlling the position of the center of body mass (CoM) allowing its ground projection to always fall inside the base of support (Winter et al 2003) and keeping the desired posture based on the appropriate alignment of body segments relative to vertical (Kristjansson and Treleaven 2009). Body anteropulsion results from the net effect of the nervous system compensation of the induced illusory lengthening of the stimulated muscles (illusory neck flexion) which, integrated with vestibular information of a vertically aligned head, corresponds to an illusory backward shift of the CoM (backward lean of the body) which might happen during a backward fall (Ivanenko et al 2000; Courtine et al 2007) This response highlights the important contribution of neck proprioception to the postural scheme used to control balance in humans (Roll et al 1989; Massion 1992; Kavounoudias et al 1999)

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