An MRI-Compatible Foot-Sole Stimulation System Enabling Characterization of the Brain Response to Walking-Related Tactile Stimuli.

Tingwei Zhang,Jue Zhang,Brad Manor,Kai Zhang,Jing Fang,Xiaoying Wang,Yufeng Chai,Yunfei Long,Junhong Zhou

doi:10.3389/fnins.2019.01075

Abstract

Foot-sole somatosensory impairment is a main contributor to balance decline and falls in aging and disease. The cortical networks involved in walking-related foot sole somatosensation, however, remain poorly understood. We thus created and tested a novel MRI-compatible device to enable study of the cortical response to pressure stimuli applied to the foot sole that mimic those stimuli experienced when walking. The device consists of a dual-drive stimulator equipped with two pneumatic cylinders, which are separately programed to apply pressure waveforms to the entire foot sole. In a sample of nine healthy younger adults, the pressure curve applied to the foot sole closely correlated with that experienced during over ground walking (r = 0.811 ± 0.043, P < 0.01). MRI compatibility testing indicated that the device has no or negligible impact on MR image quality. Gradient-recalled echo-planar images of nine healthy young adults using a block-designed 3.5-min walking-related stimulation revealed significant activation within the supplementary motor area, supramarginal gyrus, paracingulate gyri, insula, precentral gyrus, middle temporal gyrus, and hippocampus (uncorrected P < 0.001, k ≥ 10). Together, these results indicate that this stimulation system is MRI-compatible and capable of mimicking walking-related pressure waveforms on foot sole. It may thus be used as a research tool to identify cortical targets for interventions (e.g., non-invasive brain stimulation) aimed at enhancing this important source of input to the locomotor control system.

Highlights

The decline in foot-sole somatosensation is highly prevalent in older adults and is a primary contributor to diminished gait and increased risk of falling (Richardson and Hurvitz, 1995; Roll et al, 2002; Hijmans et al, 2007; Kars et al, 2009; Manor et al, 2010)
We designed a novel foot sole stimulation system to enable the study of the cortical response to walking-related foot sole pressure stimuli
We demonstrated that: (1) the pressure waveforms applied to the foot soles provided by this dual-drive stimulation system closely mimicked those experienced during over-ground walking; (2) the use of this stimulation system has no interference with the quality of MR image; and (3) the walking-related foot sole stimuli activates a distributed functional network that includes multiple motor and somatosensory cortical regions

Summary

Introduction

The decline in foot-sole somatosensation is highly prevalent in older adults and is a primary contributor to diminished gait and increased risk of falling (Richardson and Hurvitz, 1995; Roll et al, 2002; Hijmans et al, 2007; Kars et al, 2009; Manor et al, 2010). Hao et al (2013) created and validated a pneumatic tactile stimulator applying programmable single-point pressure stimuli to a small area on the plantar surface of the foot Such devices have proven to effectively activate several cortical regions, as measured by the change of intensity of BOLD signal. These previous studies focused on low-force and high-frequency stimuli, and stimulated only small surface of the foot sole, which cannot enable the recreation of the pressurewaveform change on foot soles as experienced when walking over the ground

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Discussion

Conclusion