Does tDCS Selectively Modulate the Pre-frontal Cortex Hemodynamics? An Immediate Effect-Controlled Trial on Depressed and Healthy People

Despite the recommendation to treat depression using the transcranial direct current stimulation (tDCS), novel findings raised doubts over the tDCS efficacy in managing depressive episodes. Neurophysiologic approaches to understand the specificities of brain responses to tDCS in de-pressed patients remains a feature. Objective: to compare the immediate hemodynamic responses to tDCS on left dorsolateral pre-frontal cortex (DLPFC; F3-Fp2 montage) in patients with depres-sive disorder and healthy controls (no additional stimuli). Methods: Sixteen participants were al-located in depression group and 16 in the control group. Both groups received 2mA tDCS for 20 minutes, using the F3-Fp2 montage. The hemodynamic effect over the DLPFC was assessed using near-infrared intracranial spectroscopy (NIRS) 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: Be-tween-group differences were detected for mean and minimal baseline rates of SatO2 and HbO levels. The depression group showed lower results compared to the control group. After the pro-tocol, only the depression group showed increased mean and minimal rates of SatO2 and HbO. The post-tDCS rates were equal for both groups. Conclusion: The findings showed immediate anodal tDCS effects over DLPFC hemodynamics. The effects were exclusive for the lowest base-line rates group, not affecting the normal oxygen rates group. The minimal increase of SatO2 and HbO rates after the protocol in the depression group suggests that those with reduced cerebral perfusion may be more affected by tDCS.