Research paperDecreased functional connectivity and disrupted neural network in the prefrontal cortex of affective disorders: A resting-state fNIRS study

- Raw fNIRS data were preprocessed with independent component analysis to remove global components and motion artifacts.
- Patients with affective disorders (AD) exhibited reduced intra-regionally and symmetrically interhemispheric connectivity in the prefrontal cortex.
- AD patients showed significantly lower locally functional connectivity in the right inferior frontal cortex compared to healthy controls.
- AD patients showed poor long-distance connectivity between bilateral inferior frontal gyrus.
- AD patients without medication presented more disrupted cortical organizations in the PFC than AD patients with medication.

BackgroundAffective disorders (AD) have been conceptualized as neural network-level diseases. In this study, we utilized functional near infrared spectroscopy (fNIRS) to investigate the spontaneous hemodynamic activities in the prefrontal cortex (PFC) of the AD patients with or without medications.Methods42 optical channels were applied to cover the superior frontal gyrus (SFG), middle frontal gyrus (MFG), and inferior frontal gyrus (IFG), which constitute one of the most important affective networks of the brain. We performed resting-state measurements on 28 patients who were diagnosed as having AD and 30 healthy controls (HC). Raw fNIRS data were preprocessed with independent component analysis (ICA) and a band-pass filter to remove artifacts and physiological noise.ResultsBy systematically analyzing the intra-regional, intrahemispheric, and interhemispheric connectivities based on the spontaneous oscillations of Δ[HbO], our results indicated that patients with AD exhibited significantly reduced intra-regional and symmetrically interhemispheric connectivities in the PFC when compared to HC. More specifically, relative to HC, AD patients showed significantly lower locally functional connectivity in the right IFG, and poor long-distance connectivity between bilateral IFG. In addition, AD patients without medication presented more disrupted cortical organizations in the PFC, and the severity of self-reported symptoms of depression was negatively correlated with the strength of intra-regional and symmetrically interhemispheric connectivity in the PFC.LimitationsRegarding the measuring technique, fNIRS has restricted measurement depth and spatial resolution. During the study, the subgroups of AD, such as major depressive disorder, bipolar, comorbidity, or non-comorbidity, dosage of psychotropic drugs, as well as different types of pharmacological responses were not distinguished and systematically compared. Furthermore, due to the limitation of the research design, it was still not very clear how pharmacological treatment affected the resting state cortical organization of the prefrontal lobe, and the degree of the effect in patients with AD.ConclusionThese results strongly supported that RSFC measured by fNIRS could be a useful and powerful way of delineating the neuropathology of AD.