NEUROPHYSIOLOGICAL CORRELATES OF TDCS-INDUCED MODULATION OF CORTICAL SENSORIMOTOR
NETWORKS: A SIMULTANEOUS FNIRS-EEG STUDY
Muthalib M1,3, Dutta A2,4, Besson P1, Hayashibe M2, Perrey S1
1EuroMov-M2H & 2DEMAR-INRIA, University of Montpellier, France;
3CNU, Deakin University, Australia; 4IFADO, Germany
INTRODUCTION. Non-invasive anodal transcranial direct current stimulation (atDCS) increases neuronal
excitability and activity. Recent physiological and modelling studies have shown that a 4x1 high definition
atDCS (HD-atDCS) montage can constrain the electric field between the active electrode and four
surrounding return electrodes, and thus focally stimulate a target cortical region (Edwards et al., 2013;
Muthalib et al., 2015). For HD-atDCS to be applied optimally to stimulate a target cortical region, a
neurophysiological correlate of the strength of the applied electric field should be measured during the
stimulation. The temporal and spatial changes of cortical neurovascular dynamics can be measured non-
invasively during the stimulation using fNIRS (hemodynamics) and EEG (neuronal activity) neuroimaging
methods. The aim of this study was to measure and model using combined fNIRS-EEG neuroimaging the
time course of bilateral sensorimotor network hemodynamics and neural activity during HD-atDCS
targeting the left sensorimotor cortex (SMC). METHODS.
Fifteen healthy subjects received 10min, 20min and Sham
HD-atDCS (2mA; Startstim, Neuroelectrics) targeting the left
SMC via a 4x1 HD-atDCS electrode montage (anode on C3
with four return cathode electrodes ~4cm apart, see Fig.1) in
a randomized, cross-over study design. Simultaneous EEG (23
channels; Active 2, Biosemi) and fNIRS (16 channels; Oxymon
MkIII, Artinis Medical Systems) was used to measure changes
in bilateral sensorimotor network neuronal activity (EEG
frequency) and hemodynamics (fNIRS: oxy-O2Hb and deoxy-
HHb hemoglobin concentrations). RESULTS. In general, the
O2Hb time course showed a biphasic increase in the stimulated left sensorimotor network during only the
10min and 20min HD-atDCS sessions, with a more rapid increase during the first 2-5min for the fNIRS
channels surrounding the anode (Ch3,4,5,6) than those outside the perimeter of the return electrodes
(Ch1,2,7,8) or contralateral channels (Ch9-16), which was followed by a relative plateau for the rest of the
stimulation period. The time course of HHb signals were more variable between subjects. In a subsample
of 5 subjects the EEG power spectrum analysis showed that HD-atDCS primarily modulated EEG power in
the Theta (4-7Hz) and Alpha (7-12Hz) frequency bands. A Kalman filter using an autoregressive exogenous
(ARX) model was able to appropriately track O2Hb signals using EEG band-power signals. CONCLUSION.
The temporal and spatial increase of O2Hb in the stimulated left sensorimotor network by HD-atDCS could
represent the strength of the induced electrical field, and thus provide an indication of the dose of cortical
neuromodulation. The ARX model using neuronal (EEG) and hemodynamic (fNIRS) responses can lend to
closed-loop control of HD-atDCS for optimised neuromodulation in various neuroergonomic applications.
Acknowledgements: This work was supported by LabEx NUMEV (ANR‐10‐LABX‐20).
References: Edwards, D., et al., (2013). Physiological and modeling evidence for focal transcranial
electrical brain stimulation in humans: a basis for high-definition tDCS. Neuroimage, 74, 266-275.
Muthalib, M., et al., (2015). Transcranial direct current stimulation induced modulation of cortical
haemodynamics: A comparison between time-domain and continuous-wave functional near-infrared
spectroscopy. Brain Stimul, 8, 392.
F5 F2 F6
4x1 HD-tDCS 16 fNIRS channels
23 EEG electrodes