Translational Mental Health: Towards measuring haemodynamic activity and electrophysiology at the bedside using fNIRS/EEG – An exploratory investigation in MDD patients

Major depressive disorder (MDD) is associated with alterations in intrinsic brain networks, particularly the default mode network (DMN). However, most neuroimaging evidence derives from functional magnetic resonance imaging, which is difficult to implement in routine clinical settings. Portable neuroimaging approaches such as electroencephalography (EEG) and functional near-infrared spectroscopy (fNIRS) provide complementary electrophysiological and haemodynamic measures of brain activity and may enable bedside monitoring of brain network dynamics. In this Report, we investigated the feasibility of simultaneous EEG–fNIRS recordings in patients with MDD during resting-state conditions. Resting-state data were acquired from 11 patients with MDD (8 male, 3 female; median age: 30 years, range: 18–54 years) and 11 healthy control participants (8 male, 3 female; median age: 28 years, range: 19–55 years). The acquisition system comprised 32 EEG electrodes covering the whole brain and 8 fNIRS optodes covering the DMN. EEG power spectral density was estimated using Welch’s method, with analysis focusing on alpha-band activity (8–12 Hz) in cortical regions associated with the DMN. The analysis included the electrodes Fp1, Fp2, Fz, F7, F8, F3, F4, P3, P4, T7, and T8. For fNIRS, fractional amplitude of low-frequency fluctuations (fALFF) was computed from oxyhaemoglobin signals to quantify spontaneous haemodynamic activity. Group differences were assessed using the Brunner–Munzel test, and associations with depressive symptom severity (BDI-II) were examined using Spearman correlations. Patients with MDD showed significantly reduced relative alpha power in prefrontal (Fp1, Fp2, Fz), parietal (P3, P4), and left temporal (F7, T7) regions compared with controls. In contrast, fNIRS analysis revealed increased oxyhaemoglobin fALFF in one DMN-related channel in the MDD group. Although correlations with symptom severity were not statistically significant, fNIRS measures showed positive trend-level associations with symptom severity, whereas relative EEG power spectral density showed negative trend-level associations. These findings demonstrate the feasibility of multimodal EEG–fNIRS recordings at the bedside and suggest that combined electrophysiological and haemodynamic measures may capture complementary signatures of altered resting-state brain dynamics in MDD, supporting the translational potential of portable multimodal neurophysiological assessment in psychiatric settings.