NIRS/fNIRS in Depression: HD-tDCS, Cognitive Control, and Prefrontal Connectivity

Major depressive disorder is not only a mood disorder. It can also involve attention difficulties, slower decision-making, reduced cognitive flexibility, rumination, and less energy to reorganize one’s life. The study by Hernández-Sauret, Garcia-Castro, and Redolar-Ripoll starts exactly from this point: understanding how two prefrontal regions — the DLPFC and the VLPFC — participate differently in cognitive control in people with depression.

The scientific question is excellent: does stimulating the left dorsolateral prefrontal cortex or the left ventrolateral prefrontal cortex produce different effects on mood, cognitive control, and prefrontal connectivity in patients with major depressive disorder? To answer this, the researchers combined HD-tDCS with resting-state fNIRS, clinical scales, and cognitive tasks.

The study included 26 patients with depression, divided into three groups: stimulation over the left DLPFC, stimulation over the left VLPFC, and sham stimulation. Participants received 10 consecutive HD-tDCS sessions over two weeks. They were assessed before the intervention, after the intervention, and again at one-month follow-up.

This experimental design deserves praise. The researchers did not simply ask whether depression improved or not. They tried to observe three layers at the same time: depressive symptoms, cognitive performance, and prefrontal functional reorganization. This is very important because depression is not only a subjective experience; it also changes how a person sustains goals, inhibits automatic responses, changes strategies, and maintains cognitive energy for action.

The HD-tDCS was delivered using Starstim®, by Neuroelectrics, with a 4×1 ring montage. For the DLPFC montage, the anode was placed at F3. For the VLPFC montage, the anode was placed at AF7. Stimulation was delivered at 2 mA for 20 minutes, across 10 sessions.

The fNIRS part is especially relevant for BrainLatam2026. The study used NIRSport2, by NIRx Medical Technologies, with two wavelengths, 760 nm and 850 nm, a sampling rate of 5.1 Hz, 16 sources, and 16 detectors arranged to cover the frontal cortex. The researchers also used short-separation channels to regress extracerebral hemodynamic signals, which improves the interpretation of cortical activity.

Clinically, stimulation over the DLPFC produced broader, earlier, and more sustained improvements. Depressive symptoms decreased significantly after the intervention and remained improved at one-month follow-up. The VLPFC group showed a later improvement, mainly at follow-up. The sham group did not show the same consistent clinical pattern.

In the cognitive tasks, the DLPFC appeared more related to gains in executive function, flexibility, and interference control. The study reported improvements in the Trail Making Test, fewer errors in the Wisconsin Card Sorting Task, and better performance in Stroop conditions. The VLPFC appeared more specifically related to conflict adaptation in the Attention Network Test, suggesting a more selective and delayed effect on inhibitory control.

The fNIRS result is especially interesting. There was no simple global within-group connectivity change. However, at one-month follow-up, the DLPFC group showed greater prefrontal connectivity than both the VLPFC and sham groups. This suggests that DLPFC stimulation may produce a more durable functional reorganization, not necessarily an immediate effect.

From the BrainLatam2026 perspective, we can say that the DLPFC may act as a gateway for reorganizing the Tensional Self when a person is trapped in low flexibility, low cognitive energy, and reduced capacity for updating. Depression, in this view, is not reduced to “lack of willpower” or only to “brain chemistry.” It appears as a difficult reorganization between body, attention, memory, action, and belonging.

fNIRS is useful because it measures cortical hemodynamic variation — oxyhemoglobin and deoxyhemoglobin — while we observe how the prefrontal cortex sustains or reorganizes networks. It does not measure thoughts directly, but it helps us see whether the brain is moving toward a more integrated or more rigid functional architecture.

The avatar-lens for this blog could be Tekoha + APUS. Tekoha as internal territory, APUS as body-territory. Depression can be seen as a body that has partially lost confidence to move in the world. The DLPFC, then, is not only an “executive region.” It becomes a possible axis of re-entry into planning, choice, inhibition of automatic patterns, and recovery of a future.

The generous decolonial critique is that the study is excellent, but still observes depression mainly inside an individual clinical frame. BrainLatam2026 would expand the question: what happens to prefrontal connectivity when a person, beyond neuromodulation, also recovers belonging, social safety, regulated breathing, and a concrete possibility of reorganizing life?

A future experimental design could combine HD-tDCS + fNIRS + EEG + HRV/RMSSD + respiration + GSR + EMG. fNIRS would measure prefrontal oxygenation and connectivity. EEG could follow attention and cognitive processing markers. HRV/RMSSD and respiration would indicate autonomic regulation. GSR would show sympathetic activation. Facial or cervical EMG could reveal silent bodily tensions associated with Tensional Selves.

The bridge with DREX Cidadão appears when we understand that mental health also depends on social metabolism. A citizen without minimum safety, income, belonging, or horizon lives under continuous tension. DREX Cidadão, as a proposal for the State’s metabolic function, could reduce social anergy and allow more Zone 2: more fruition, more metacognition, more critical capacity, and more life reorganization.

The article itself recognizes important limits: small sample size, three-group division, and the need for larger studies with longer follow-up. Therefore, the findings are promising but still preliminary. The strength of the study is showing that DLPFC and VLPFC should not be treated as if they were the same thing. Prefrontal stimulation needs to become increasingly precise, both in cortical target and clinical question.

Closing for blog/live:
This study shows that depression can be investigated as a difficulty of reorganization between mood, cognitive control, and prefrontal connectivity. HD-tDCS tests causal modulation; fNIRS shows hemodynamic dynamics; and BrainLatam2026 expands the question: it is not enough to know which region to stimulate. We also need to ask what body, what territory, what belonging, and what public policy allow the brain to breathe again in Zone 2.

Single Reference
Hernández-Sauret, A., Garcia-Castro, G., & Redolar-Ripoll, D. E. (2026). Dissociating the Role of Dorsolateral Prefrontal Cortex and Ventrolateral Prefrontal Cortex in Cognitive Control in Depression: A Combined HD-tDCS and fNIRS Study. Brain Topography, 39, 2. https://doi.org/10.1007/s10548-025-01157-4