Somatosensory Event-related Potentials from Orofacial Skin Stretch Stimulation

Summary

This paper introduces a method for obtaining somatosensory event-related potentials following orofacial skin stretch stimulation. The current method can be used to evaluate the contribution of somatosensory afferents to both speech production and speech perception.

Abstract

Cortical processing associated with orofacial somatosensory function in speech has received limited experimental attention due to the difficulty of providing precise and controlled stimulation. This article introduces a technique for recording somatosensory event-related potentials (ERP) that uses a novel mechanical stimulation method involving skin deformation using a robotic device. Controlled deformation of the facial skin is used to modulate kinesthetic inputs through excitation of cutaneous mechanoreceptors. By combining somatosensory stimulation with electroencephalographic recording, somatosensory evoked responses can be successfully measured at the level of the cortex. Somatosensory stimulation can be combined with the stimulation of other sensory modalities to assess multisensory interactions. For speech, orofacial stimulation is combined with speech sound stimulation to assess the contribution of multi-sensory processing including the effects of timing differences. The ability to precisely control orofacial somatosensory stimulation during speech perception and speech production with ERP recording is an important tool that provides new insight into the neural organization and neural representations for speech.

Introduction

Speech production is dependent on both auditory and somatosensory information. The auditory and somatosensory feedback occur in combination from the earliest vocalizations produced by an infant and both are involved in speech motor learning. Recent results suggest that somatosensory processes contribute to perception as well as production. For example, the identification of speech sounds is altered when a robotic device stretches the facial skin as participants listen to auditory stimuli¹. Air puffs to the cheek that coincide with auditory speech stimuli alter participants' perceptual judgments².

These somatosensor....

Protocol

The current experimental protocol follows the guidelines of ethical conduct according to the Yale University Human Investigation Committee.

1. Electroenchephalopgaphy (EEG) Preparation

1. Measure head size to determine the appropriate EEG cap.
2. Identify the location of the vertex by finding the mid-point between nasion and inion with a measuring tape.
3. Place the EEG cap on the head using the pre-determined vertex as Cz. Examine Cz again after placing the cap by using a measuring tape as done in 1.2. Note that the EEG cap is equipped with electrode holders and the placement of the 64 electrodes (or holders) is based on a modified 10-20....

Results

This section presents representative event-related potentials in response to somatosensory stimulation resulting from facial skin deformation. The experimental setup is represented in Figure 1. Sinusoidal stimulation was applied to the facial skin lateral to the oral angle (See Figure 3A as reference). One hundred stretch trials were recorded for each participant with 12 participants tested in total. After removing the trials with blinks and eye movement .......

Discussion

The studies reported here provide evidence that precisely controlled somatosensory stimulation that is produced by facial skin deformation induces cortical ERPs. Cutaneous afferents are known as a rich source of kinesthetic information^3,4 in human limb movement^5,6 and speech movement^7,8,21. Stretching the facial skin in a manner that reflects the actual movement direction during speaking induces a kinesthetic sense similar to the corresponding movement. The current method combining precis.......

Materials

List of materials used in this article

Name	Company	Catalog Number	Comments
EEG recording system	Biosemi	ActiveTwo
Robotic decice for skin stretch	Geomagic	Phantom Premium 1.0
EEG-compatible earphones	Etymotic research	ER3A
Software for visual and auditory stimulation	Neurobehavioral Systems	Presentation
Electrode gel	Parker Laboratories, INC	Signa gel
Double sided tape	3M	1522
Disposable syringe	Monoject	412 Curved Tip
Analog input device	National Instuments	PCI-6036E
Degital output device	Measurement computing	USB-1208FS