Introduction : La narcolepsie et l'hypersomnie idiopathique sont des troubles d'hypersomnie centrale peu compris, caractérisés par une somnolence diurne excessive causant des perturbations majeures au niveau du fonctionnement diurne et de la qualité de vie. Bien que certains aspects cliniques soient propres à chaque condition, plusieurs caractéristiques se chevauchent et ces dernières demeurent très difficile à diagnostiquer adéquatement. Le manque de distinction entre les troubles d'hypersomnolence centrale est extrêmement problématique, limitant la compréhension des mécanismes physiopathologiques sous- jacents. Objectif : À l'aide de la morphométrie cérébrale, l'objectif de l'étude est d'établir des différences anatomiques (c.-à-d., épaisseur corticale, volume sous-cortical) entre la narcolepsie avec cataplexie (NT1), la narcolepsie sans cataplexie (NT2), l'hypersomnie idiopathique (HI) et des participants en santé contrôles dans diverses régions du cerveau qui sont fonctionnellement liées au sommeil et au maintien de l'éveil. Méthodes : Une séquence d’acquisition d’images IRM anatomiques pondérées en T1 fut acquise sur 15 patients NT1, 15 NT2, 15 HI et 15 participants contrôles en santé (n = 60). Les images anatomiques furent traitées avec la suite logicielle FreeSurfer (FreeSurfer version 6.0.1) afin d'obtenir des mesures d'épaisseur corticale et de volume sous-cortical. Les mesures morphométriques obtenus pour différentes régions furent comparées entre les groupes par ANOVAs, ajustées pour l'âge. Résultats : Les résultats ont démontré une réduction volumétrique de la matière grise dans plusieurs structures sous-corticales associées au sommeil et au maintien de l'éveil dont l'hypothalamus et l'amygdale pour les patients NT1 et les patients NT2, comparés aux participants contrôles en santé. Les patients HI quant à eux n'ont pas démontré de différence volumétrique au niveau de l'hypothalamus comparativement aux participants contrôles, mais plutôt une diminution du volume de l'amygdale et du noyau accumbens, des structures associées à un réseau fonctionnel modulant la vigilance. Aucune différence significative d'épaisseur corticale n'a été retrouvée entre les groupes. Conclusion : Les résultats montrent des changements neuroanatomiques distincts entre les patients NT1 et HI, suggérant des mécanismes physiopathologiques différents et soulignent le phénotype hétérogène des patients NT2. / Introduction : Narcolepsy and idiopathic hypersomnia are poorly understood central disorders of hypersomnolence characterized by excessive daytime sleepiness leading to severe daytime disturbances and poor quality of life. Although some clinical features are specific to each condition, many characteristics overlap, and a reliable diagnosis remains difficult to achieve. The lack of clinical distinction between central disorders of hypersomnolence is extremely problematic and hinders the understanding of their underlying pathophysiological mechanisms. Objective : Using brain morphometry, the objective of this study is to establish anatomical differences (i.e., cortical thickness and subcortical volume) between narcolepsy with cataplexy (NT1), narcolepsy without cataplexy (NT2), idiopathic hypersomnia (HI) and healthy controls in brain regions involved in the modulation of sleep and wakefulness. Methods : T1-weighted MRI sequences were acquired in 15 NT1 patients, 15 NT2, 15 HI and 15 healthy controls (n = 60). Anatomical images were preprocessed using the FreeSurfer software package (FreeSurfer version 6.0.1) to obtain measures of cortical thickness and subcortical volume. Group differences in brain morphometric measurements acquired for different brain regions were analyzed using ANOVAs, adjusted for age. Results : Results displayed reduced gray matter volume in subcortical structures associated with the modulation of sleep and wakefulness, including the hypothalamus and the amygdala in NT1 and NT2 patients, compared to healthy controls. On the other hand, HI patients did not show volume changes in the hypothalamus compared to healthy controls, but instead showed a volume reduction of the amygdala and the nucleus accumbens, both structures associated with a functional network involved in the modulation of alertness. No significant group difference in cortical thickness was found. Conclusion : These results show distinct neuroanatomical changes between NT1 patients and HI patients, suggesting separate pathophysiological mechanisms and underline the heterogeneous phenotype of NT2 patients.

Despite the interest in the neuroimaging of working memory, little is still known about the neurobiology of complex working memory in tasks that require simultaneous manipulation and storage of information. In addition to the central executive network, we assumed that the recently described salience network [involving the anterior insular cortex (AIC) and the anterior cingulate cortex (ACC)] might be of particular importance to working memory tasks that require complex, effortful processing. Method: Healthy participants (n = 26) and participants suffering from working memory problems related to the Kleine–Levin syndrome (KLS) (a specific form of periodic idiopathic hypersomnia; n = 18) participated in the study. Participants were further divided into a high- and low-capacity group, according to performance on a working memory task (listening span). In a functional magnetic resonance imaging (fMRI) study, participants were administered the reading span complex working memory task tapping cognitive effort. Principal findings: The fMRI-derived blood oxygen level dependent (BOLD) signal was modulated by (1) effort in both the central executive and the salience network and (2) capacity in the salience network in that high performers evidenced a weaker BOLD signal than low performers. In the salience network there was a dichotomy between the left and the right hemisphere; the right hemisphere elicited a steeper increase of the BOLD signal as a function of increasing effort. There was also a stronger functional connectivity within the central executive network because of increased task difficulty. Conclusion: The ability to allocate cognitive effort in complex working memory is contingent upon focused resources in the executive and in particular the salience network. Individual capacity during the complex working memory task is related to activity in the salience (but not the executive) network so that high-capacity participants evidence a lower signal and possibly hence a larger dynamic response.