198 Chapter 7 We identified the behavioural performance indices and neural correlates of varying vigilance need and of changes over time (time-on-task effects) reflecting different stages of attention in people with narcolepsy type 1 and healthy controls. Error-related brain activity was also compared between groups by adding participants’ error scores as covariates of interest to the analyses of the main effects, i.e., task vs. baseline. We hypothesized that people with narcolepsy type 1 would show lower activity than controls in the cinguloopercular and arousal networks when performing the task, particularly in the higher difficulty level. People with narcolepsy were also expected to have lower activity within these networks when progressing the task. Materials and Methods Participants Twelve adults with narcolepsy type 1 were recruited through the outpatient clinic of Sleep-Wake Centre SEIN (The Netherlands) and twelve age and sex group-matched healthy participants were recruited through local newspaper advertisements. People with narcolepsy type 1 were diagnosed according to the 3rd edition of the International Classification of Sleep Disorders (ICSD3) [8]. All participants had to be 18-65 years old, right-handed and have normal or corrected-to-normal vision. Those with narcolepsy type 1 needed to be treatment-naïve or treatment-free for at least two weeks before MRI acquisition. Exclusion criteria consisted of current psychotropic drug usage, present diagnosis of a serious comorbidity, contraindications for MRI scanning and macroscopic structural brain abnormalities (tumours, ventricle enlargement, cortical atrophy, or vascular lesions). As described in the ICSD-3 diagnostic criteria, the cerebrospinal fluid (CSF) hypocretin-1 levels of the three people with narcolepsy type 1 without clear-cut cataplexy were determined. Notably, one patient had a concentration (138 pg/mL) slightly above the threshold according to international standards of 110 pg/mL for narcolepsy type 1 [46]. This individual was not excluded because the clinical phenotype was typical and the hypocretin-1 level still deficient. The same population of participants was previously studied using diffusion tensor imaging to analyse microstructural white matter integrity [238]. Before image acquisition, the Dutch version of the National Adult Reading Test [216] was administered to assess intelligence (IQ) and the Epworth Sleepiness Scale (ESS) was used to measure daytime sleepiness [217]. All data collection was performed during the afternoon to account for possible circadian effects. Participants were asked to refrain from caffeine-containing substances
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