Effect of anodal tDCS on human prefrontal cortex observed by fNIRS

Transcranial direct current stimulation (tDCS) is one of the noninvasive brain stimulation methods that have been used to study many neuropsychiatric and neurological disorders in humans. tDCS can excite or inhibit the neurons depending upon its polarity. In this study, we have investigated the effect of anodal tDCS on human prefrontal cortex using functional near-infrared spectroscopy (fNIRS), which is a noninvasive neuroimaging technique. We have developed a new wireless fNIRS system compatible with EEG, and also developed a pad-type tDCS with variable current limits. Our wireless fNIRS system is composed of a microcontroller, an optical probe, tri-wavelength light emitting diodes (LEDs), photodiodes, WiFi communication module and battery. The developed tDCS system can generate the current in the range of 0.8 ~ 2.2 mA. To test the functionality of the systems, fNIRS data was recorded before and after the tDCS stimulation. The results of this study show that the anodal tDCS excites the neurons in the region of interest and this excitability is monitored using the fNIRS system.