Lingual electrotactile discrimination ability is associated with the presence of specific connective tissue structures (papillae) on the tongue surface.

Tyler S Allison,Philip Turk,Joel Moritz,Leslie M Stone-Roy,Laurens W J Bosman

doi:10.1371/journal.pone.0237142

Abstract

Electrical stimulation of nerve endings in the tongue can be used to communicate information to users and has been shown to be highly effective in sensory substitution applications. The anterior tip of the tongue has very small somatosensory receptive fields, comparable to those of the finger tips, allowing for precise two-point discrimination and high tactile sensitivity. However, perception of electrotactile stimuli varies significantly between users, and across the tongue surface. Despite this, previous studies all used uniform electrode grids to stimulate a region of the dorsal-medial tongue surface. In an effort to customize electrode layouts for individual users, and thus improve efficacy for sensory substitution applications, we investigated whether specific neuroanatomical and physiological features of the tongue are associated with enhanced ability to perceive active electrodes. Specifically, the study described here was designed to test whether fungiform papillae density and/or propylthiouracil sensitivity are positively or negatively associated with perceived intensity and/or discrimination ability for lingual electrotactile stimuli. Fungiform papillae number and distribution were determined for 15 participants and they were exposed to patterns of electrotactile stimulation (ETS) and asked to report perceived intensity and perceived number of stimuli. Fungiform papillae number and distribution were then compared to ETS characteristics using comprehensive and rigorous statistical analyses. Our results indicate that fungiform papillae density is correlated with enhanced discrimination ability for electrical stimuli. In contrast, papillae density, on average, is not correlated with perceived intensity of active electrodes. However, results for at least one participant suggest that further research is warranted. Our data indicate that propylthiouracil taster status is not related to ETS perceived intensity or discrimination ability. These data indicate that individuals with higher fungiform papillae number and density in the anterior medial tongue region may be better able to use lingual ETS for sensory substitution.

Highlights

Sensory systems are crucial for providing individuals with information about both the internal and external environments, and are needed to assess and respond to stimuli
The results indicated that participants with more Fungiform papillae (FP) were better able to discriminate active electrodes, relative to participants with fewer FP (Table 3 Fig 9, P-value = 0.0203)
In the experiments described here, we tested whether fungiform papillae (FP) density and distribution or the ability to detect 6-propylthiouracil (PROP) are associated with perception and discrimination ability of electrotactile stimuli on the tongue

Summary

Introduction

Sensory systems are crucial for providing individuals with information about both the internal and external environments, and are needed to assess and respond to stimuli. Bach-y-Rita was among the first to suggest that the adult brain is plastic enough for sensory cortices to decode neural impulses from an alternate sensory modality when a primary modality has been damaged He demonstrated this notion through experiments in which blindfolded subjects were able to discriminate differences in object form when visual information from a camera was translated into vibrational patterns applied to the skin of the subject’s back [3, 4]. Since Bach-y-Rita’s initial development of his vision substitution device, multiple groups have worked on improving sensory substitution devices (SSDs) to allow for practical use beyond the laboratory While many of these devices focus on cutaneous tactile stimulation of the back or hand [20,21,22,23,24,25,26,27,28], electrotactile stimulation (ETS) of the tongue has certain advantages. Other vision substitution applications appear promising [48,49,50,51] and additional applications include improving typing efficiency for people with upper limb mobility impairments [52], and even providing guidance during surgeries [53]

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