Neuroimaging correlates of narcolepsy with cataplexy: A systematic review

Regional cerebral blood perfusion impairment in type 1 narcolepsy patients: An arterial spin labeling study

OBJECTIVE

To investigate the pathophysiological characteristics of cerebral blood flow (CBF) in patients with narcolepsy type 1 (NT1) via the arterial spin labeling (ASL) technique.

METHODS

Thirty patients with diagnostic NT1 (PTs) and 34 age- and sex-matched healthy controls (HCs) were recruited for this study. Basic information was collected, and clinical evaluation and neuroimaging, including ASL and T1-3DBRAVO, was performed. The z-normalized CBF (zCBF) and spatial coefficient of variation (sCoV) were calculated, and the changes in NT1 were compared via analysis of covariate (ANCOVA). Furthermore, spearman's correlation analysis between impaired regional perfusion and clinical features was performed. Age, sex, and normalized grey matter volume were included as covariates.

RESULTS

Compared with that of HCs, the zCBF of PTs significantly differed in regions of fronto-temporal-occipital cortex, right insula and posterior insula, and left rostral/dorsal anterior cingulate gyrus (ACG) (P < 0.006). Moreover, the sCoV was significantly altered in the frontotemporal cortex, rostral ACG, right hippocampus, and posterior insula (P < 0.003). In PTs, positive correlations were identified between the zCBF of the right superior/middle frontal gyrus (SFG/MFG) and mean sleep latency, and between the zCBF of the left SFG of the frontal pole and sleep hallucination severity. Moreover, the sCoV of the right MFG/hippocampus were positively associated with Rapid Eye Movement efficiency and negatively associated with Hamilton Anxiety Scale score, respectively.

CONCLUSION

PTs exhibited abnormal regional perfusion in the frontal-temporal-occipital cortex and limbic system regions, which may serve as patient-specific imaging markers. Alterations in perfusion may lead to the clinical manifestations of underlying psychological and sleep disorders in PTs.

The Past and Future of Sleep Medicine

The past of sleep medicine is rich with seminal discoveries, from the recognition of clinical syndromes to measurement of sleep itself to classic and novel therapeutics. Advances in neurobiology have mapped a number of sleep circuits, described the central and peripheral circadian system, and identified the cause of narcolepsy with cataplexy. Sleep apnea endotypes and phenotypes now have established clinical relevance, though treatment implications are a work in progress. Artificial intelligence will continue to change sleep medicine in a number of domains from aiding scoring to health outcome predictions. There is a large gap between the known science and clinical translational.

MRS study on the correlation between frontal GABA+/Glx ratio and abnormal cognitive function in medication-naive patients with narcolepsy

OBJECTIVE

To compare the GABA+/Glx (glutamate-glutamine) ratio in the prefrontal lobe under non-rapid eye movement sleep between patients with narcolepsy type 1 (NT1) and normal controls and explore the correlation between this difference and abnormal cognitive function, using synchronous electroencephalography-functional magnetic resonance spectroscopy (EEG-fMRS).

METHODS

MRS measurements of GABA+ and Glx concentrations as well as synchronous EEG data were obtained from 26 medication-naive patients with NT1 and 29 sex- and age-matched healthy community volunteers. Cognition was appraised with the Beijing version of the Montreal Cognitive Assessment, and daytime sleepiness was measured using the Epworth Sleepiness Scale. All subjects recorded a 2-week sleep log as well as an overnight polysomnography within 1 week before MR scanning to understand their sleep habits and determine sleep stages. After PSG, they also underwent multiple sleep latency trials. Patient/control group differences in the individual measurements of GABA+ and Glx and the GABA+/Glx ratio and their relationship with cognition were assessed.

RESULTS

The GABA+/Glx ratio and GABA + levels of patients with narcolepsy were higher than those of the control group (P＜0.0001 and P = 0.0008, respectively). However, there was no significant difference in Glx levels (P = 0.6360). The GABA+/Glx ratio negatively correlated with abnormal cognitive function (r = -0.6710, P = 0.0002). Moreover, GABA + levels were inversely proportional to rapid eye movement sleep latency (REML) in patients with narcolepsy (r = -0.5019, P = 0.0106).

CONCLUSION

The GABA+/Glx ratio in the prefrontal lobe was higher in NT1 patients during N2 sleep than in normal controls, mainly caused by GABA + levels; this ratio was negatively related to abnormal cognitive function. In addition, GABA + levels were inversely proportional to REML.

Cortical thickness and sub-cortical volumes in post-H1N1 narcolepsy type 1: A brain-wide MRI case-control study

OBJECTIVE

There was more than a 10-fold increase in the incidence of narcolepsy type 1 (NT1) after the H1N1 mass vaccination in 2009/2010 in several countries. NT1 is associated with loss and increase of cell groups in the hypothalamus which may be associated with secondary affected sub-cortical and cortical gray matter. We performed a case-control comparison of MRI-based global and sub-cortical volume and cortical thickness in post-H1N1 NT1 patients compared with controls.

METHODS

We included 54 post-H1N1 NT1 patients (51 with confirmed hypocretin-deficiency; 48 H1N1-vaccinated with Pandemrix®; 39 females, mean age 21.8 ± 11.0 years) and 114 healthy controls (77 females, mean age 23.2 ± 9.0 years). 3T MRI brain scans were obtained, and the T1-weighted MRI data were processed using FreeSurfer. Group differences among three global, 10 sub-cortical volume measures and 34 cortical thickness measures for bilateral brain regions were tested using general linear models with permutation testing.

RESULTS

Patients had significantly thinner brain cortex bilaterally in the temporal poles (Cohen's d = 0.68, p = 0.00080), entorhinal cortex (d = 0.60, p = 0.0018) and superior temporal gyrus (d = 0.60, p = 0.0020) compared to healthy controls. The analysis revealed no significant group differences for sub-cortical volumes.

CONCLUSIONS

Post-H1N1(largely Pandemrix®-vaccinated) NT1 patients have significantly thinner cortex in temporal brain regions compared to controls. We speculate that this effect can be partly attributed to the hypothalamic neuronal change in NT1, including loss of function of the widely projecting hypocretin-producing neurons and secondary effects of the abnormal sleep-wake pattern in NT1 or could be specific for post-H1N1 (largely Pandemrix®-vaccinated) NT1 patients.

Microstructural White Matter Abnormalities in Children and Adolescents With Narcolepsy Type 1

BACKGROUND

In 2010, the H1N1 Pandemrix vaccination campaign was followed by a sudden increase in narcolepsy type 1 (NT1). We investigated the brain white matter microstructure in children with onset of NT1 within two years after the Pandemrix vaccination.

METHODS

We performed diffusion-weighted magnetic resonance imaging (MRI) on 19 children and adolescents with NT1 and 19 healthy controls. Imaging was performed at a median of 4 years after the diagnosis at a median age of 16 years. For the MRI, we used whole-brain tractography and tract-based spatial statistics (TBSS). We compared these results with medical records and questionnaire data.

RESULTS

Narcoleptic children showed a global decrease in mean, axial, and radial diffusivity and an increase in planarity coefficient in the white matter TBSS skeleton and tractography. These differences were widespread, and there was an increased asymmetry of the mean diffusivity in children with NT1. The global microstructural metrics were reflected in behavior, and especially the axial diffusion levels correlated with anxiety and depression symptoms and social and behavioral problems.

CONCLUSIONS

In pediatric patients with Pandemrix-associated NT1, several global changes in the brain white matter network skeleton were observed within five years after the onset of NT1. The degree of changes correlates with behavioral problems.

Assessing resting-state brain functional connectivity in adolescents and young adults with narcolepsy using functional near-infrared spectroscopy

This study aimed to elucidate the alterations in the prefrontal cortex's functional connectivity and network topology in narcolepsy patients using functional near-infrared spectroscopy (fNIRS). Twelve narcolepsy-diagnosed patients from Guangxi Zhuang Autonomous Region's People's Hospital Sleep Medicine Department and 11 matched healthy controls underwent resting fNIRS scans. Functional connectivity and graph theory analyses were employed to assess the prefrontal cortex network's properties and their correlation with clinical features. Results indicated increased functional connectivity in these adolescent and young adult patients with narcolepsy, with significant variations in metrics like average degree centrality and node efficiency, particularly in the left middle frontal gyrus. These alterations showed correlations with clinical symptoms, including depression and sleep efficiency. However, the significance of these findings was reduced post False Discovery Rate adjustment, suggesting a larger sample size is needed for validation. In conclusion, the study offers initial observations that alterations in the prefrontal cortex's functional connectivity may potentially act as a neurobiological indicator of narcolepsy, warranting further investigation with a larger cohort to substantiate these findings and understand the underlying mechanisms.

Resting-State Functional Magnetic Resonance Imaging as an Indicator of Neuropsychological Changes in Type 1 Narcolepsy

RATIONALE AND OBJECTIVES

To explore indicators of neuropsychological changes in patients with type 1 narcolepsy (NT1) using resting-state functional magnetic resonance imaging (rs-fMRI).

MATERIALS AND METHODS

Thirty-four NT1 patients and 34 age- and sex-matched healthy volunteers were recruited for neuropsychiatric assessments and rs-fMRI data acquisition. Fractional amplitude of low-frequency fluctuations (fALFF), regional homogeneity (ReHo), and related brain functional connectivity (FC) were calculated for the two groups and compared using a two-sample t test with cluster-level FDR correction. Moreover, partial correlation analysis was performed between these functional values of changed brain regions and clinical scales.

RESULTS

Compared to those of healthy controls, spontaneous functional activities were significantly weakened in patients with NT1 in regions such as the left/right posterior cerebellum lobe, left inferior temporal gyrus, and left dorsolateral superior frontal gyrus, whereas those in regions such as the left middle occipital gyrus, right inferior occipital gyrus, and left/right lingual gyrus were significantly strengthened. Furthermore, NT1 patients displayed significantly changed FCs between the left/right anterior cingulate gyrus (ACG) and regions such as the left/right cerebellum, left middle occipital gyrus, and left inferior frontal gyrus in the operculum. In partial correlation analysis, the functions in the left dorsolateral superior frontal gyrus were significantly related to the Trail Making Tests (TMT) score. Moreover, the FC between the left ACG and left inferior frontal gyrus in the operculum was highly correlated with anxiety and depression features, including the Hamilton Anxiety Scale (HAMA) score and Hamilton Depression Rating Scale (HAMD-17) score.

CONCLUSION

Patients with NT1 exhibited abnormalities in the anterior cingulate cortex, frontal-parietal cortex, hippocampus, and left/right posterior cerebellum lobe. The deactivation of the left frontal-temporal cortex is stronger, which is involved in the cognitive decline and mental disorders in these patients. Damage to the ACG may affect its FC with other regions and cause cognition and emotion dysregulation, perhaps by impairing patients' visual pathways and frontal-temporal-parietal networks. Hence, these could be important biomarkers for their neuropsychological changes.

Single sessions of transcranial direct current stimulation and transcranial random noise stimulation exert no effect on sleepiness in patients with narcolepsy and idiopathic hypersomnia

Background

Hypersomnia poses major challenges to treatment providers given the limitations of available treatment options. In this context, the application of non-invasive brain stimulation techniques such as transcranial electrical stimulation (tES) may open up new avenues to effective treatment. Preliminary evidence suggests both acute and longer-lasting positive effects of transcranial direct current stimulation (tDCS) on vigilance and sleepiness in hypersomniac patients. Based on these findings, the present study sought to investigate short-term effects of single sessions of tDCS and transcranial random noise stimulation (tRNS) on sleepiness in persons suffering from hypersomnia.

Methods

A sample of 29 patients suffering from narcolepsy or idiopathic hypersomnia (IH) was recruited from the Regensburg Sleep Disorder Center and underwent single sessions of tES (anodal tDCS, tRNS, sham) over the left and right dorsolateral prefrontal cortex on three consecutive days in a double-blind, sham-controlled, pseudorandomized crossover trial. The primary study endpoint was the mean reaction time measured by the Psychomotor Vigilance Task (PVT) before and directly after the daily tES sessions. Secondary endpoints were additional PVT outcome metrics as well as subjective outcome parameters (e.g., Karolinska Sleepiness Scale; KSS).

Results

There were no significant treatment effects neither on objective (i.e., PVT) nor on subjective indicators of sleepiness.

Conclusion

We could not demonstrate any clinically relevant effects of single sessions of tDCS or tRNS on objective or subjective measures of sleepiness in patients with hypersomnia. However, we cannot exclude that repeated sessions of tES may affect vigilance or sleepiness in hypersomniac patients.

Larger hypothalamic volume in narcolepsy type 1

STUDY OBJECTIVES

Narcolepsy type 1 (NT1) is a neurological sleep disorder. Postmortem studies have shown 75%-90% loss of the 50 000-70 000 hypocretin-producing neurons and 64%-94% increase in the 64 000-120 000 histaminergic neurons and conflicting indications of gliosis in the hypothalamus of NT1 patients. The aim of this study was to compare MRI-based volumes of the hypothalamus in patients with NT1 and controls in vivo.

METHODS

We used a segmentation tool based on deep learning included in Freesurfer and computed the volume of the whole hypothalamus, left/right part of the hypothalamus, and 10 hypothalamic subregions. We included 54 patients with post-H1N1 NT1 (39 females, mean age 21.8 ± 11.0 years) and 114 controls (77 females, mean age 23.2 ± 9.0 years). Group differences were tested with general linear models using permutation testing in Permutation Analysis of Linear Models and evaluated after 10 000 permutations, yielding two-tailed P-values. Furthermore, a stepwise Bonferroni correction was performed after dividing hypothalamus into smaller regions.

RESULTS

The analysis revealed larger volume for patients compared to controls for the whole hypothalamus (Cohen's d = 0.71, p = 0.0028) and for the left (d = 0.70, p = 0.0037) and right part of the hypothalamus (d = 0.65, p = 0.0075) and left (d = 0.72, p = 0.0036) and right tubular-inferior (d = 0.71, p = 0.0037) hypothalamic subregions.

CONCLUSIONS

In conclusion, patients with post-H1N1 NT1 showed significantly larger hypothalamic volume than controls, in particular in the tubular-inferior subregions which could reflect several processes as previous studies have indicated neuroinflammation, gliosis, and changes in the numbers of different cell types.

Sleep Stage Transitions and Sleep-Dependent Memory Consolidation in Children with Narcolepsy-Cataplexy

Electroencephalographic sleep stage transitions and altered first REM sleep period transitions have been identified as biomarkers of type 1 narcolepsy in adults, but not in children. Studies on memory complaints in narcolepsy have not yet investigated sleep-dependent memory consolidation. We aimed to explore stage transitions; more specifically altered REM sleep transition and its relationship with sleep-dependent memory consolidation in children with narcolepsy. Twenty-one children with narcolepsy-cataplexy and twenty-three healthy control children completed overnight polysomnography and sleep-dependent memory consolidation tests. Overnight transition rates (number of transitions per hour), global relative transition frequencies (number of transitions between a stage and all other stages/total number of transitions × 100), overnight transitions to REM sleep (transition from a given stage to REM/total REM transitions × 100), and altered first REM sleep period transitions (transitions from wake or N1 to the first REM period) were computed. Narcoleptic children had a significantly higher overnight transition rate with a higher global relative transition frequencies to wake. A lower sleep-dependent memory consolidation score found in children with narcolepsy was associated with a higher overnight transition frequency. As observed in narcoleptic adults, 90.48% of narcoleptic children exhibited an altered first REM sleep transition. As in adults, the altered sleep stage transition is also present in children with narcolepsy-cataplexy, and a higher transition rate could have an impact on sleep-dependent memory consolidation. These potential biomarkers could help diagnose type 1 narcolepsy in children more quickly; however, further studies with larger cohorts, including of those with type 2 narcolepsy and hypersomnia, are needed.

Characteristics of hypersomnia due to inflammatory demyelinating diseases of the central nervous system

Background

Neuromyelitis optica spectrum disorder (NMOSD) diagnostic criteria for inflammatory demyelinating central nervous system diseases included symptomatic narcolepsy; however, no relevant case-control studies exist. We aimed to examine the relationship among cerebrospinal fluid orexin-A (CSF-OX) levels, cataplexy and diencephalic syndrome; determine risk factors for low-and-intermediate CSF-OX levels (≤200 pg/mL) and quantify hypothalamic intensity using MRI.

Methods

This ancillary retrospective case-control study included 50 patients with hypersomnia and 68 controls (among 3000 patients) from Akita University, the University of Tsukuba and community hospitals (200 facilities). Outcomes were CSF-OX level and MRI hypothalamus-to-caudate-nucleus-intensity ratio. Risk factors were age, sex, hypersomnolence and MRI hypothalamus-to-caudate-nucleus-intensity ratio >130%. Logistic regression was performed for the association between the risk factors and CSF-OX levels ≤200 pg/mL.

Results

The hypersomnia group (n=50) had significantly more cases of NMOSD (p<0.001), diencephalic syndrome (p=0.006), corticosteroid use (p=0.011), hypothalamic lesions (p<0.023) and early treatment (p<0.001). No cataplexy occurred. In the hypersomnia group, the median CSF-OX level was 160.5 (IQR 108.4-236.5) pg/mL and median MRI hypothalamus-to-caudate-nucleus-intensity ratio was 127.6% (IQR 115.3-149.1). Significant risk factors were hypersomnolence (adjusted OR (AOR) 6.95; 95% CI 2.64 to 18.29; p<0.001) and MRI hypothalamus-to-caudate-nucleus-intensity ratio >130% (AOR 6.33; 95% CI 1.18 to 34.09; p=0.032). The latter was less sensitive in predicting CSF-OX levels ≤200 pg/mL. Cases with MRI hypothalamus-to-caudate-nucleus-intensity ratio >130% had a higher rate of diencephalic syndrome (p<0.001, V=0.59).

Conclusions

Considering orexin as reflected by CSF-OX levels and MRI hypothalamus-to-caudate-nucleus-intensity ratio may help diagnose hypersomnia with diencephalic syndrome.

Amygdala neurocircuitry at the interface between emotional regulation and narcolepsy with cataplexy

Narcolepsy is a sleep disorder characterized by chronic and excessive daytime sleepiness, and sudden intrusion of sleep during wakefulness that can fall into two categories: type 1 and type 2. Type 1 narcolepsy in humans is widely believed to be caused as a result of loss of neurons in the brain that contain the key arousal neuropeptide Orexin (Orx; also known as Hypocretin). Patients with type 1 narcolepsy often also present with cataplexy, the sudden paralysis of voluntary muscles which is triggered by strong emotions (e.g., laughter in humans, social play in dogs, and chocolate in rodents). The amygdala is a crucial emotion-processing center of the brain; however, little is known about the role of the amygdala in sleep/wake and narcolepsy with cataplexy. A collection of reports across human functional neuroimaging analyses and rodent behavioral paradigms points toward the amygdala as a critical node linking emotional regulation to cataplexy. Here, we review the existing evidence suggesting a functional role for the amygdala network in narcolepsy, and build upon a framework that describes relevant contributions from the central nucleus of the amygdala (CeA), basolateral amygdala (BLA), and the extended amygdala, including the bed nucleus of stria terminalis (BNST). We propose that detailed examinations of amygdala neurocircuitry controlling transitions between emotional arousal states may substantially advance progress in understanding the etiology of narcolepsy with cataplexy, leading to enhanced treatment opportunities.

Increased very low frequency pulsations and decreased cardiorespiratory pulsations suggest altered brain clearance in narcolepsy

Background

Narcolepsy is a chronic neurological disease characterized by daytime sleep attacks, cataplexy, and fragmented sleep. The disease is hypothesized to arise from destruction or dysfunction of hypothalamic hypocretin-producing cells that innervate wake-promoting systems including the ascending arousal network (AAN), which regulates arousal via release of neurotransmitters like noradrenalin. Brain pulsations are thought to drive intracranial cerebrospinal fluid flow linked to brain metabolite transfer that sustains homeostasis. This flow increases in sleep and is suppressed by noradrenalin in the awake state. Here we tested the hypothesis that narcolepsy is associated with altered brain pulsations, and if these pulsations can differentiate narcolepsy type 1 from healthy controls.

Methods

In this case-control study, 23 patients with narcolepsy type 1 (NT1) were imaged with ultrafast fMRI (MREG) along with 23 age- and sex-matched healthy controls (HC). The physiological brain pulsations were quantified as the frequency-wise signal variance. Clinical relevance of the pulsations was investigated with correlation and receiving operating characteristic analysis.

Results

We find that variance and fractional variance in the very low frequency (MREG_vlf) band are greater in NT1 compared to HC, while cardiac (MREG_card) and respiratory band variances are lower. Interestingly, these pulsations differences are prominent in the AAN region. We further find that fractional variance in MREG_vlf shows promise as an effective bi-classification metric (AUC = 81.4%/78.5%), and that disease severity measured with narcolepsy severity score correlates with MREG_card variance (R = −0.48, p = 0.0249).

Conclusions

We suggest that our novel results reflect impaired CSF dynamics that may be linked to altered glymphatic circulation in narcolepsy type 1.

The flow of fluid surrounding and inside the human brain is thought to be caused by the movement of brain vessels, breathing and heart rate. These so called brain pulsations are linked to clearing waste from the brain. This process is increased during sleep and suppressed while we are awake. Narcolepsy is a neurological disease where the brain areas regulating being awake and asleep are affected. The diagnosis requires time-consuming hospital tests and is often delayed which has a prolonged negative impact on the patients. Here, we use brain imaging to investigate whether brain pulsations are altered in patients with narcolepsy, and if they can be utilized to differentiate patients with narcolepsy from healthy individuals. We find that narcolepsy affects all brain pulsations, and these findings show promise as an additional diagnostic tool that could help detect the disease earlier.

Järvelä et al. investigate if narcolepsy is associated with altered brain pulsations using ultrafast fMRI. They find differences in the brain pulsations between narcolepsy type 1 patients and healthy controls that may link to altered brain clearance in narcolepsy, have diagnostic potential and correlate with the severity of narcolepsy.

Is memory impaired in narcolepsy type 1?

Memory deficits in narcolepsy with cataplexy type 1 (NT1) have been poorly studied, and the results are controversial. Patients with NT1 usually report memory deficits, which are not seen in objective memory assessments. This study aimed to assess attention and memory processes in NT1 patients using standardised neuropsychological tests and to compare the results with a control group. Performance in memory and attention tests was studied in 12 NT1 patients (diagnosed according to ICSD-3 criteria) and the results compared with those of 14 control subjects. All participants completed questionnaires on sleepiness and depression symptoms. Significant differences were found in the depression symptoms questionnaire. Regarding neuropsychological assessment, NT1 patients performed worse in attention than the control group in that they processed fewer stimuli and achieved fewer correct stimuli. However, no significant differences were found in the memory test results, and the performance was similar between both groups. After application of the Holm-Bonferroni correction, the only differences that remained significant were those in the ESS and in BDI-II scores. Our results showed that memory processes are preserved in NT1 patients and that memory complaints may not be associated with an objective memory deficit. In addition, the significant difference observed for patients in the depression questionnaire could explain the subjective memory complaints.

Sleep Dysfunction and Grey Matter Volume

PURPOSE OF REVIEW

With the voxel-based morphometry (VBM), structural imaging studies turned into new directions aiming to explore neurological disorders differently. This approach helps identify possible pathophysiological correlations between neuroanatomical grey matter (GM) structures in patients with sleep dysfunction. This article reviews recent findings on GM structure in various sleep disorders and possible causes of disturbed sleep and discusses the future perspectives.

RECENT FINDINGS

At present, research on the effect of GM volume changes in specific brain areas on the pathogenesis of sleep disturbances is incomplete. It remains unknown if the GM thickness reduction in patients with REM sleep behaviour disorder, obstructive sleep apnea, restless legs syndrome, and insomnia is due to complex disease presentation or direct response to disturbed sleep. Additionally, many VBM studies have yielded inconsistent results showing either reduction or increase in GM. The spatiotemporal complexity of whole-brain networks and state transitions during sleep and the role of GM changes increase new debates. Having multimodal data from large sample studies can help model sleep network dynamics in different disorders and provide novel data for possible therapeutic interventions.

Hypothalamus and amygdala functional connectivity at rest in narcolepsy type 1

INTRODUCTION

functional and structural MRI studies suggest that the orexin (hypocretin) deficiency in the dorso-lateral hypothalamus of narcoleptic patients would influence both brain metabolism and perfusion and would cause reduction in cortical grey matter. Previous fMRI studies have mainly focused on cerebral functioning during emotional processing. The aim of the present study was to explore the hemodynamic behaviour of spontaneous BOLD fluctuation at rest in patients with Narcolepsy type 1 (NT1) close to disease onset.

METHODS

Fifteen drug naïve children/adolescents with NT1 (9 males; mean age 11.7 ± 3 years) and fifteen healthy children/adolescents (9 males; mean age 12.4 ± 2.8 years) participated in an EEG-fMRI study in order to investigate the resting-state functional connectivity of hypothalamus and amygdala. Functional images were acquired on a 3 T system. Seed-based functional connectivity analyses were performed using SPM12. Regions of Interest were the lateral hypothalamus and the amygdala.

RESULTS

compared to controls, NT1 patients showed decreased functional connectivity between the lateral hypothalamus and the left superior parietal lobule, the hippocampus and the parahippocampal gyrus. Decreased functional connectivity was detected between the amygdala and the post-central gyrus and several occipital regions, whereas it was increased between the amygdala and the inferior frontal gyrus, claustrum, insula, and putamen.

CONCLUSION

in NT1 patients the abnormal connectivity between the hypothalamus and brain regions involved in memory consolidation during sleep, such as the hippocampus, may be linked to the loss of orexin containing neurons in the dorsolateral hypothalamus. Moreover, also functional connectivity of the amygdala seems to be influenced by the loss of orexin-containing neurons. Therefore, we can hypothesize that dysfunctional interactions between regions subserving the maintenance of arousal, memory and emotional processing may contribute to the main symptom of narcolepsy.

Compromised Dynamic Cerebral Autoregulation in Patients With Central Disorders of Hypersomnolence

Objective: We aimed to investigate the dynamic cerebral autoregulation (dCA) in patients with central disorders of hypersomnolence during wakefulness.

Methods: Thirty-six patients with central disorders of hypersomnolence were divided into three groups according to polysomnography and multiple sleep latency test results: the idiopathic hypersomnia group (IH), narcolepsy type 1 without rapid-eye-movement sleep behavior disorder group (NT1-RBD), and narcolepsy type 1 with rapid-eye-movement sleep behavior disorder group (NT1 + RBD), with 12 patients in each group. Twelve sex- and age-matched healthy controls were recruited. We assessed the Epworth sleepiness scale (ESS) and dCA of all subjects. dCA was assessed by analyzing the phase difference (PD) using transfer function analysis. The ESS and dCA were analyzed before and after standardized treatment in 24 patients with narcolepsy type 1.

Results: The overall PD of the IH, NT1-RBD, and NT1 + RBD groups were lower than that of the control group (P < 0.001). There were no significant differences between the overall PD of the NT1-RBD and NT1 + RBD group (P > 0.05). The ESS scores decreased and the overall PD increased after treatment in 24 patients with narcolepsy type 1 (P < 0.001). Multivariable analysis showed that mean sleep latency in multiple sleep latency test was independently associated with impaired overall PD (P < 0.05).

Conclusions: The dCA is impaired in patients with central disorders of hypersomnolence. The impairment of dCA occurs irrespective of NT1-RBD/+RBD. The ESS score and dCA improved in patients with narcolepsy type 1 after medication treatment. The mean sleep latency in multiple sleep latency test was independently associated with impaired dCA.

Clinical Trial Registration:www.ClinicalTrials.gov, identifier: NCT02752139.

Lag Analysis of Fast fMRI Reveals Delayed Information Flow Between the Default Mode and Other Networks in Narcolepsy

Narcolepsy is a chronic neurological disease characterized by dysfunction of the hypocretin system in brain causing disruption in the wake-promoting system. In addition to sleep attacks and cataplexy, patients with narcolepsy commonly report cognitive symptoms while objective deficits in sustained attention and executive function have been observed. Prior resting-state functional magnetic resonance imaging (fMRI) studies in narcolepsy have reported decreased inter/intranetwork connectivity regarding the default mode network (DMN). Recently developed fast fMRI data acquisition allows more precise detection of brain signal propagation with a novel dynamic lag analysis. In this study, we used fast fMRI data to analyze dynamics of inter resting-state network (RSN) information signaling between narcolepsy type 1 patients (NT1, n = 23) and age- and sex-matched healthy controls (HC, n = 23). We investigated dynamic connectivity properties between positive and negative peaks and, furthermore, their anticorrelative (pos-neg) counterparts. The lag distributions were significantly (P < 0.005, familywise error rate corrected) altered in 24 RSN pairs in NT1. The DMN was involved in 83% of the altered RSN pairs. We conclude that narcolepsy type 1 is characterized with delayed and monotonic inter-RSN information flow especially involving anticorrelations, which are known to be characteristic behavior of the DMN regarding neurocognition.

Activity dynamics of amygdala GABAergic neurons during cataplexy of narcolepsy

Recent studies showed activation of the GABAergic neurons in the central nucleus of the amygdala (CeA) triggered cataplexy of sleep disorder narcolepsy. However, there is still no direct evidence on CeA GABAergic neurons’ real-time dynamic during cataplexy. We used a deep brain calcium imaging tool to image the intrinsic calcium transient as a marker of neuronal activity changes in the narcoleptic VGAT-Cre mice by expressing the calcium sensor GCaMP6 into genetically defined CeA GABAergic neurons. Two distinct GABAergic neuronal groups involved in cataplexy were identified: spontaneous cataplexy-ON and predator odor-induced cataplexy-ON neurons. Majority in the latter group were inactive during regular sleep/wake cycles but were specifically activated by predator odor and continued their intense activities into succeeding cataplexy bouts. Furthermore, we found that CeA GABAergic neurons became highly synchronized during predator odor-induced cataplexy. We suggest that the abnormal activation and synchronization of CeA GABAergic neurons may trigger emotion-induced cataplexy.

Independent Component Analysis and Graph Theoretical Analysis in Patients with Narcolepsy

The present study was aimed to evaluate resting-state functional connectivity and topological properties of brain networks in narcolepsy patients compared with healthy controls. Resting-state fMRI was performed in 26 adult narcolepsy patients and 30 matched healthy controls. MRI data were first analyzed by group independent component analysis, then a graph theoretical method was applied to evaluate the topological properties in the whole brain. Small-world network parameters and nodal topological properties were measured. Altered topological properties in brain areas between groups were selected as region-of-interest seeds, then the functional connectivity among these seeds was compared between groups. Partial correlation analysis was performed to evaluate the relationship between the severity of sleepiness and functional connectivity or topological properties in the narcolepsy patients. Twenty-one independent components out of 48 were obtained. Compared with healthy controls, the narcolepsy patients exhibited significantly decreased functional connectivity within the executive and salience networks, along with increased functional connectivity in the bilateral frontal lobes within the executive network. There were no differences in small-world network properties between patients and controls. The altered brain areas in nodal topological properties between groups were mainly in the inferior frontal cortex, basal ganglia, anterior cingulate, sensory cortex, supplementary motor cortex, and visual cortex. In the partial correlation analysis, nodal topological properties in the putamen, anterior cingulate, and sensory cortex as well as functional connectivity between these regions were correlated with the severity of sleepiness (sleep latency, REM sleep latency, and Epworth sleepiness score) among narcolepsy patients. Altered connectivity within the executive and salience networks was found in narcolepsy patients. Functional connection changes between the left frontal cortex and left caudate nucleus may be one of the parameters describing the severity of narcolepsy. Changes in the nodal topological properties in the left putamen and left posterior cingulate, changes in functional connectivity between the left supplementary motor area and right occipital as well as in functional connectivity between the left anterior cingulate gyrus and bilateral postcentral gyrus can be considered as a specific indicator for evaluating the severity of narcolepsy.

Structural anomaly in the reticular formation in narcolepsy type 1, suggesting lower levels of neuromelanin

The aim of this study was to investigate structural changes in the brain stem of adolescents with narcolepsy, a disorder characterized by excessive daytime sleepiness, fragmented night-time sleep, and cataplexy. For this purpose, we used quantitative magnetic resonance imaging to obtain R1 and R2 relaxation rates, proton density, and myelin maps in adolescents with narcolepsy (n = 14) and healthy controls (n = 14). We also acquired resting state functional magnetic resonance imaging (fMRI) for brainstem connectivity analysis. We found a significantly lower R2 in the rostral reticular formation near the superior cerebellar peduncle in narcolepsy patients, family wise error corrected p = .010. Narcolepsy patients had a mean R2 value of 1.17 s^-1 whereas healthy controls had a mean R2 of 1.31 s^-1, which was a large effect size with Cohen d = 4.14. We did not observe any significant differences in R1 relaxation, proton density, or myelin content. The sensitivity of R2 to metal ions in tissue and the transition metal ion chelating property of neuromelanin indicate that the R2 deviant area is one of the neuromelanin containing nuclei of the brain stem. The close proximity and its demonstrated involvement in sleep-maintenance, specifically through orexin projections from the hypothalamus regulating sleep stability, as well as the results from the connectivity analysis, suggest that the observed deviant area could be the locus coeruleus or other neuromelanin containing nuclei in the proximity of the superior cerebellar peduncle. Hypothetically, the R2 differences described in this paper could be due to lower levels of neuromelanin in this area of narcolepsy patients.

Temporal Course of Cerebral Autoregulation in Patients With Narcolepsy Type 1: Two Case Reports

Cerebral autoregulation is the mechanism by which constant cerebral blood flow is maintained despite changes in arterial blood pressure. In the two presented cases, cerebral autoregulation was impaired in patients with narcolepsy type 1, and both venlafaxine and fluoxetine may have the potential to improve the impaired cerebral autoregulation. A relationship may exist between impaired cerebral autoregulation and neurological symptoms in patients with narcolepsy type 1.