However, the functional connectivity has not yet been investigated in depth. Recently, 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). Multichannel NIRS is an emerging neuroimaging tool that in addition to detecting the spatiotemporal characteristics of brain function using a non-invasive, portable, and restraint-free technique ( 5), has been validated in psychiatry patients ( 6). The association between prefrontal cortex (PFC) activation and depressive symptoms has also been investigated using near-infrared spectroscopy (NIRS). Earlier studies have used functional magnetic resonance imaging (fMRI) to reveal reduced prefrontal activation during digit-sorting tasks ( 1) and verbal fluency tasks (VFTs) ( 2), imbalance between left and right prefrontal activation during emotional judgment ( 3), and reduced activation in the right nucleus accumbens during the monetary incentive delay task ( 4).
When compared to healthy individuals, patients with MDD have been reported to display aberrant neuropsychological characteristics. Studies comparing patients and healthy controls have reported that these impairments are associated with abnormal patterns of brain activity. Impairments in cognitive functions, such as attention, working memory, and executive function, have been reportedly observed in patients with major depressive disorder (MDD). The efficiency of the functional network may play an important role in the understanding of depressive symptoms. Network measures can quantitatively characterize the reduction in functional connectivity caused by depression. The patterns of prefrontal functional connectivity differed significantly between the patient and control groups during the VFT. Moreover, efficiency, the network measure related to the effectiveness of information transfer, showed a significant between-group difference along with a strong negative correlation with depression severity (rho = −0.30, p = 0.009). 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. Hemodynamics and functional connectivity across eight prefrontal subregions in the two groups were analyzed and compared. 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. The evaluation of functional connectivity during a cognitive task can be used to explain the neurocognitive mechanism underlying the cognitive impairments caused by depression. The graph-theoretical approach provides useful network metrics for evaluating functional connectivity.
7Department of Psychiatry, Inje University Ilsan Paik Hospital, Goyang, South Koreaĭeviations 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.6Department of Psychology, University of Wisconsin-Milwaukee, Milwaukee, WI, United States.
5Clinical Emotion and Cognition Research Laboratory, Inje University, Goyang, South Korea.4Department of Psychology, Penn State University, State College, PA, United States.3Department of Psychology, University of Notre Dame, Dame, RI, United States.1Department of Information Technology Engineering, Sookmyung Women's University, Seoul, South Korea.Suh-Yeon Dong 1, JongKwan Choi 2, Yeonsoo Park 3, Seung Yeon Baik 4, Minjee Jung 5, Yourim Kim 6 and Seung-Hwan Lee 5,7 *
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