Effects of ON and OFF subthalamic nucleus deep brain stimulation on cortical activation during finger movements tasks: a simultaneous fNIRS and EEG study

Abstract

s / Brain Stimulation 8 (2015) 378e394 393 Continuous-wave (CW) fNIRS measures light attenuation through both the cortical and superficial (e.g., skin) tissues, while timedomain (TD) fNIRS directly measures the photon time-of flight that contains information about the depth probed by photons in the tissue, and in turn provides a possibility to separate the superficial from the cortical layer haemodynamic signals. Therefore, the aim of this study was to compare the changes in resting cortical haemodynamics measured by a CW and TDfNIRS system during anodal tDCS. Methods: A Startstim tDCS system (Neuroelectrics) was used to deliver a constant direct current (2mA) to the left sensorimotor cortex (SMC) via an anodal 4x1 high definition (HD)-tDCS electrode montage. During 10min of anodal HD-tDCS, changes in resting oxygenated (O2Hb) and deoxygenated (HHb) haemoglobin concentrations from the left and right SMC were monitored by a CWfNIRS system (Oxymon MK III, AMS) and in a subsequent session with a TD-fNIRS system (Politecnico di Milano). Results/Discussion: CWand TDfNIRS showed a similar time course (i.e. increase in O2Hb from baseline with no or only minimal decrease in HHb) in the stimulated left SMC (no or only minimal changes in right SMC) over the 10min of anodal HD-tDCS (Fig. a, b). The TD-fNIRS confirmed this time course in the cortical layer of the stimulated left SMC (Fig. d), but the changes were much smaller than the superficial layer changes (Fig. b). Conclusion: This preliminary study has shown that 10min of anodal HD-tDCS induces an increase in activation in the cortical layer of the stimulated left SMC.