Purpose: Daytime complaints such as memory and attention deficits and failure to accomplish daily tasks are common in insomnia patients. However, objective psychological tests to detect cognitive impairment are equivocal. Neural function associated with cognitive performance may explain the discrepancy. The aim of this study was to investigate the hemodynamic response patterns of patients with chronic insomnia disorder (CID) using the noninvasive and low-cost functional neuroimaging technique of multichannel near-infrared spectroscopy (NIRS) in order to identify changes of neural function associated with cognitive performance.
Patients and methods: Twenty-four CID patients and twenty-five healthy controls matched for age, right-hand dominance, educational level, and gender were examined during verbal fluency tasks (VFT) using NIRS. A covariance analysis was conducted to analyze differences of oxygenated hemoglobin (oxy-Hb) changes in prefrontal cortex (PFC) between the two groups and reduce the influence of the severity of depression. Pearson correlation coeffcients were calculated to examine the relationship between the oxy-Hb changes, with the severity of insomnia and depressive symptoms assessed by the Pittsburgh Sleep Quality Index (PSQI) and the Hamilton Rating Scale for Depression (HAMD).
Results: The number of words generated during the VFT in CID groups showed no statistical differences with healthy controls. CID patients showed hypoactivation in the PFC during the cognitive task. In addition, we found that the function of left orbitofrontal cortex (OFC) during the VFT was significantly negatively correlated with the PSQI scores and the function of right dorsolateral PFC (DLPFC) was significantly negatively correlated with the HAMD scores.
Conclusion: The present study detected dysfunctions in PFC in spite of intact performance which indicates the role of PFC in the neurophysiological underpinnings. Left OFC function is associated with insomnia symptoms and right DLPFC function is associated with depressive symptoms.
Keywords: chronic insomnia disorder, near-infrared spectroscopy, NIRS, prefrontal cortex, verbal fluency task, depressive symptoms