As consensus has not yet been achieved, the mechanistic and neurophysiologic approach to understanding specificities of brain responses to tDCS stimuli in patients with depression compared to controls continues to stand as a key feature for continuous basic and clinical research. The effects of tDCS on cortical neurovascular tissue go beyond the impacts on neuronal activity [7]. Instead, there is evidence that tDCS neurovascular modulation targets the entire tissue: the neurons, glia, endothelial cells, and the extracellular processes involved in brain transport, such as changes in viscosity accompanied by changes in the osmotic flow [8; 9]. The complex interaction among these factors would provoke specific responses in each person, mainly driven by the subject's baseline characteristics or even by the type of disorder affecting the neural system [10]. Neurovascular modulation is a widely discussed topic concerning cortical response to tDCS in patients with depression [8]. Marked abnormalities were found in patients with depression compared to those without depression, mainly in blood oxygen rates of the bilateral ventrolateral prefrontal cortex and bilateral dorsolateral prefrontal cortex (DLPFC) [11]. As these patients exhibit dysregulated cerebral blood flow [12]--which is a major and distinctive pattern compared to people without depression, hemodynamic balance would be essential to provide tissue homeostasis followed by disease-associated behavioral improvements. Functional near-infrared spectroscopy (fNIRS) is a non-invasive optical imaging technique that relies on the difference in the absorption of NIR light between oxyhemoglobin (HbO) and deoxyhemoglobin (HbR) [13]. The technique quantifies the hemoglobin concentration changes using variations in the absorbed light intensity measured by emitting continuous wave light through the skull into the brain [11; 14]. The fNIRS technique has been proposed as a less expensive alternative over fMRI to assess brain blood flow [13]. However, fNIRS has usually been used in combination with cognitive or motor tasks in order to activate specific cortical regions of interest without isolating the tDCS effect itself. Other approaches to clarify the tDCS's effects on brain hemodynamics in people with and without depression would allow clearer clinical perspectives on tDCS's usefulness in patients with depression. SatO\({}_{2}\) refers to the percentage of hemoglobin that is saturated with oxygen relative to the total hemoglobin (both oxygenated and deoxygenated). It provides a snapshot of the efficiency of oxygen delivery and utilization in the brain. High oxygen saturation levels generally indicate adequate oxygenation, while low levels may signal hypoxia or impaired oxygen delivery. SatO\({}_{2}\) also indicates the proportion of oxygenated hemoglobin, but it does not give information about the actual amount of oxygen being transported. A high saturation percentage could be misleading if the total hemoglobin is low, resulting in insufficient oxygen supply despite high saturation [10; 11; 15; 16; 17]. The HbO level indicates the absolute concentration of oxygenated hemoglobin in the blood, providing information about the total amount of oxygen being carried by the blood to the brain, which is crucial for understanding the brain's oxygen supply. High levels of oxyhemoglobin reflect good oxygen delivery, while low levels may indicate inadequate oxygenation. HbO is the absolute amount of oxygen available in the blood, which is crucial for understanding the actual oxygen delivery capacity. It can also indicate adequate or inadequate oxygen delivery regardless of the saturation percentage. For instance, high oxyhemoglobin levels ensure adequate oxygen supply even if saturation varies within normal limits [10; 11; 15; 16; 17]. Thus, the primary aim of the present study was to compare the immediate differences in response to applying tDCS over the left DLPFC (F3-Fp2 montage) in patients with depressive disorder and without (controls) with no additional stimuli.