Does the Transcranial Direct Current Stimulation Selectively Modulate Prefrontal Cortex Hemodynamics? An Immediate Effect-Controlled Trial on People with and without Depression

Despite the recommendation to treat depression using transcranial direct current stimulation (tDCS), novel findings raise doubts over the tDCS’s efficacy in managing depressive episodes. Neurophysiologic approaches to understanding the specificities of brain responses to tDCS in patients with depression remain to be explored. Objective: Our aim was to compare immediate hemodynamic responses to tDCS on the left dorsolateral prefrontal cortex (DLPFC; F3-Fp2 montage) in patients with depressive disorder and in controls (no additional stimuli). Methods: Sixteen participants were allocated to the depression group and sixteen to the control group. Both groups received 2 mA tDCS for 20 min, using the F3-Fp2 montage. The hemodynamic effect over the DLPFC was assessed using functional near-infrared intracranial spectroscopy (fNIRS) positioned on the left supraorbital region (Fp1). Mean, minimal, and maximal values of baseline and post-stimulation rates of oxygen saturation (SatO2) were recorded. The oxygenated hemoglobin rates (HbO) were extracted. Results: Between-group differences were detected for minimal baseline rates of SatO2 and HbO levels. The depression group showed lower results compared to the control group at baseline. After the protocol, only the depression group showed increased minimal rates of SatO2 and HbO. The post-tDCS minimal rates were equal for both groups. Conclusions: The findings showed immediate anodal tDCS effects over DLPFC hemodynamics. The effects were exclusive to the lowest baseline rate group and did not affect the normal oxygen rate group. The minimal increase in SatO2 and HbO rates after the protocol in the depression group suggests that those with reduced cerebral perfusion may be more affected by tDCS.