Abstract
Objective: Simultaneous electroencephalography (EEG) and functional magnetic resonance imaging (fMRI) were applied to investigate the abnormalities in the topological characteristics of functional brain networks during non-rapid eye movement(NREM)sleep. And we investigated its relationship with cognitive abnormalities in patients with narcolepsy type 1 (NT1) disorder in the current study.Methods: The Beijing version of the Montreal Cognitive Assessment (MoCA-BJ) and EEG-fMRI were applied in 25 patients with NT1 and 25 age-matched healthy controls. All subjects participated in a nocturnal video polysomnography(PSG)study, and total sleep time (TST), percentage of TST (%TST) for each sleep stage and arousal index were calculated. The Epworth Sleepiness Score (ESS) was used to measure the degree of daytime sleepiness. The EEG-fMRI study was performed simultaneously using a 3T MRI system and a 32-channel MRI-compatible EEG system during sleep. Visual scoring of EEG data was used for sleep staging. Cognitive function was assessed for all subjects using the MoCA-BJ. The fMRI data were applied to establish a whole-brain functional connectivity network for all subjects, and the topological characteristics of the whole-brain functional network were analyzed using a graph-theoretic approach. The topological parameters were compared between groups. Lastly, the correlation between topological parameters and the assessment scale using Montreal Cognition was analyzed.Results: The MoCA-BJ scores were lower in patients with NT1 than in normal controls. Whole-brain global efficiency during stage N2 sleep in patients with NT1 displayed significantly lower small-world properties than in normal controls. Whole-brain functional network global efficiency in patients with NT1 was significantly correlated with MoCA-BJ scores.Conclusion: The global efficiency of the functional brain network during stage N2 sleep in patients with NT1 and the correspondingly reduced small-world attributes were associated with cognitive impairment.
Highlights
NT1 is a chronic neurological disorder characterized by irresistible daytime sleepiness, cataplexy, sleep hallucinations, sleep paralysis, and nocturnal sleep disturbances [1]
We excluded 19 participants: 4 patients with NT1 disorder and 3 volunteers withdrew from the PSG examination, and 7 patients and 5 volunteers failed to fall asleep, were unable to enter the N2 phase of sleep, or had excessive head motion resulted in failure to obtain fMRI data containing the complete sleep stage
The Montreal Cognitive Assessment Beijing (MoCA-BJ) score was significantly lower in the patient with NT1 disorder group than in the control group (P < 0.001)
Summary
NT1 is a chronic neurological disorder characterized by irresistible daytime sleepiness, cataplexy, sleep hallucinations, sleep paralysis, and nocturnal sleep disturbances [1]. Functional (fMRI) studies based on intercerebral connectivity have revealed impairment in the executive attention network [15] and abnormal functional connectivity [16, 17] in patients with NT1 disorder, and the presence of an alternative neural circuit that controls emotional responses to emotional challenges [18]. Patients with NT1 disorder have a cortical neural network involved in the processing of rewards and emotions [19] with lower thresholds [20] or overactivation, associated with cataplexy [21, 22]. Other studies have reported that alterations in brain connectivity and topology of some brain regions in patients with NT1 disorder are associated with lethargy, depression, and impulsive behavior [23]
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