Clinical Neuroscience
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A novel ring electrode setup for the recording of somatosensory evoked potentials during transcranial direct current stimulation (tDCS)

https://doi.org/10.1016/j.jneumeth.2012.10.006Get rights and content

Abstract

Transcranial direct current stimulation (tDCS) modulates cortical excitability thereby influencing behavior and learning. While previous studies focused on tDCS after-effects, limited information about “online” tDCS effects is available. This in turn is an important prerequisite to better characterize and/or optimize tDCS effects. Here, we aimed to explore the feasibility of recording low-artifact somatosensory evoked potentials (SEPs) during tDCS using a novel ring electrode setup. We recorded SEP before, during and after 10 min of anodal or sham tDCS using a full-band direct current (DC) EEG system in a total number of 3 subjects. SEPs were recorded in the bore of the tDCS ring electrode. Using this approach, no tDCS-induced artifacts could be observed after the application of a standard EEG filter. This new setup might help to better characterize how tDCS alters evoked brain responses thus providing novel insight into underlying physiological effects during stimulation.

Highlights

tDCS is increasingly used in cognitive and clinical neuroscience to modulate neural activity. ► Neurophysiological monitoring of tDCS effects would help to better understand the underlying mechanisms. ► We established a new combined tDCS/somatosensory evoked potentials (SEP) setup using a novel tDCS ring electrode. ► This new setup allows low-artifact SEP recordings during tDCS in direct proximity to the stimulation electrode.

Introduction

Transcranial direct current stimulation (tDCS) has the capacity to locally alter brain activation and has been shown to modulate behavior in perceptual, motor and cognitive domains (for review, Jacobson et al., 2012). Furthermore, it could be shown that anodal tDCS facilitates learning processes thus providing a potential adjuvant tool in neurorehabilitation (for review, Reis et al., 2008). Along with the increasing use of tDCS as an effective and easy-to-use brain stimulation technique, there is an increasing interest to better understand and/or monitor neurophysiological effects of tDCS.

One potential marker to detect changes in brain states induced by tDCS represents the recording of evoked potentials on the human scalp using EEG (Accornero et al., 2007, Antal et al., 2004, Wirth et al., 2011). In the somatosensory domain, a modulatory tDCS effect in a pre/post setting that influences evoked brain responses has been highlighted. For example, it has been shown that tDCS can modulate somatosensory evoked potentials (SEPs) after the application of anodal tDCS over primary sensorimotor cortex (Matsunaga et al., 2004).

Apart from studies that aim to investigate neurophysiological consequences of tDCS, it seems worthwhile to develop novel tools that allow to perform a neurophysiological monitoring of somatosensory evoked potentials during brain stimulation. We here introduce a new tDCS setup that is capable of measuring online-EEG activity/evoked potentials in direct spatial proximity to a stimulating tDCS electrode. We provide exemplary data demonstrating the feasibility of acquiring low-artifact SEP recordings over the primary somatosensory cortex (S1) during stimulation of the adjacent cortex with anodal tDCS.

Section snippets

Participants

Online tDCS effects on SEP recordings were tested in 3 neurologically healthy subjects (29 ± 3 years (mean ± standard deviation), 1 female). They gave written informed consent to participate in the study. All subjects were right-handed as assessed by the Edinburgh handedness scale (Oldfield, 1971). Prior to participation, all subjects underwent a comprehensive neurological examination to screen for potential exclusion criteria for brain stimulation. They were not taking any medication. Subjects

Results

tDCS application during SEP recordings resulted in moderate stimulus artifacts as seen in Fig. 2A. However, the application of a standard 3rd order band-pass Butterworth filter (1–250 Hz) eliminated largely these tDCS-induced interferences on SEP recordings. Hence, using a ring electrode tDCS application it is possible to maintain the physiological SEP signal without substantial changes in waveform configuration including SEP amplitudes (see Fig. 2A). Both single subject and grand average SEP

Discussion and summary

Here, we designed a new combined tDCS/EEG setup with a tDCS ring electrode allowing for online SEP recordings in close spatial proximity to the stimulating electrode. SEPs during median nerve stimulation were recorded with low artifacts within the bore of the tDCS electrode during the application of tDCS.

There is an increasing use of tDCS in different domains of cognitive and clinical neurosciences offering the possibility to locally modulate brain activity and measure behavioral consequences.

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