Abstract
Deviations in activation patterns and functional connectivity have been observed in patients with major depressive disorder (MDD) with prefrontal hemodynamics of patients compared with healthy individuals. The graph-theoretical approach provides useful network metrics for evaluating functional connectivity. The evaluation of functional connectivity during a cognitive task can be used to explain the neurocognitive mechanism underlying the cognitive impairments caused by depression. Overall, 31 patients with MDD and 43 healthy individuals completed a verbal fluency task (VFT) while wearing a head-mounted functional near-infrared spectroscopy (fNIRS) devices. Hemodynamics and functional connectivity across eight prefrontal subregions in the two groups were analyzed and compared. We observed a reduction in prefrontal activation and weaker overall and interhemispheric subregion-wise correlations in the patient group compared with corresponding values in the control group. Moreover, efficiency, the network measure related to the effectiveness of information transfer, showed a significant between-group difference [t (71.64) = 3.66, corrected p < 0.001] along with a strong negative correlation with depression severity (rho = −0.30, p = 0.009). The patterns of prefrontal functional connectivity differed significantly between the patient and control groups during the VFT. Network measures can quantitatively characterize the reduction in functional connectivity caused by depression. The efficiency of the functional network may play an important role in the understanding of depressive symptoms.
Highlights
Impairments in cognitive functions, such as attention, working memory, and executive function, have been reportedly observed in patients with major depressive disorder (MDD)
Studies using near-infrared spectroscopy (NIRS) have reported a reduction in prefrontal hemodynamic activation in patients with MDD during the verbal fluency task (VFT), along with a strong negative correlation between the severity of depression and changes in oxygenated hemoglobin (HbO2) (7–9)
The participants’ symptoms of depression and anxiety were assessed using the Hamilton Depression Rating Scale (HAMD) (27), Hamilton Anxiety Rating Scale (HAMA) (28), Beck Depression Inventory (BDI-II) (29), and State-Trait Anxiety Inventory (STAI) (30), which was composed of two subscales (STAI-state and STAI-trait, respectively)
Summary
Impairments in cognitive functions, such as attention, working memory, and executive function, have been reportedly observed in patients with major depressive disorder (MDD). Studies comparing patients and healthy controls have reported that these impairments are associated with abnormal patterns of brain activity. When compared to healthy individuals, patients with MDD have been reported to display aberrant neuropsychological characteristics. The association between prefrontal cortex (PFC) activation and depressive symptoms has been investigated using near-infrared spectroscopy (NIRS). Studies using NIRS have reported a reduction in prefrontal hemodynamic activation in patients with MDD during the VFT, along with a strong negative correlation between the severity of depression and changes in oxygenated hemoglobin (HbO2) (7–9). Some recent studies have characterized distinct resting-state MRI based-functional connectivity in patients with MDD (10), apathetic depression (11), and remitted MDD (12). Kawano et al reported a strong negative correlation between the HAMD-21 score and average HbO2 concentration in the frontal lobe (9); they did not assess the functional connectivity
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