Fluctuations of attention network activation during the resting state reflect fluctuations in subjective attentional state.

peer reviewe

Superior longitudinal fasciculus microstructure and its functional triple-network mechanisms in depressive rumination

Depressive rumination, which involves a repetitive focus on one's distress, is associated with function connectivity disturbances of Default-Mode, Salience, and Executive-Control networks, comprising the so-called "triple-network" of attention. Missing, however, is a multimodal account of rumination that neuroanatomically explains the perseveration of these dysfunctional networks as a stable human trait. Using diffusion and functional Magnetic Resonance Imaging, we explored multimodal relationships between rumination severity, white-matter microstructure, and resting-state functional connectivity in N=39 depressed adults, and then directly replicated our findings in a demographically-matched, independent sample (N=39). Among the fully-replicated results, three core findings emerged. First, rumination severity is associated with both disintegrated and desegregated functional connectivity of the triple-network. Second, global microstructural inefficiency of the right Superior Longitudinal Fasciculus (SLF) provides a neuroanatomical connectivity basis for rumination and accounts for anywhere between 25-37% of the variance in rumination (Discovery: p corr<0.01; Replication: p corr<0.01; MSE=0.05). Finally, microstructure of the right SLF and auxiliary white-matter is strongly associated with functional connectivity biomarkers of rumination, both within and between components of the triple-network (Discovery: R²=0.36, p corr<0.05; Replication: R²=0.25, p corr<0.05; MSE=0.04-0.06). By cross-validating discovery with replication, our findings advance a reproducible microstructural-functional brain connectivity model of depressive rumination that unifies neurodevelopmental and neurocognitive perspectives.Psycholog

Structural and functional brain connectivity abnormalities associated with adolescent conduct disorder in females

Background: Antisocial behavior (ASB) in childhood and adolescence is indexed by the diagnosis of conduct disorder (CD) and is associated with high rates of comorbid mental disorders, such as anxiety, depression, alcohol and drug dependence, as well as maltreatment. Elevated levels of psychopathic traits further complicate the clinical picture of adolescents with CD. Those who persist with severe ASB into adulthood will meet criteria for antisocial personality disorder (ASPD). Others will continue to display less severe ASB, and thereby not meet the diagnostic criteria for ASPD, but will experience a wide range of adverse outcomes, including persisting comorbid mental disorders and impaired psychosocial adjustment. Many studies have explored neural abnormalities associated with ASB, yet there are several key gaps in the extant literature: (I) Females with ASB have rarely been studied. (II) There has been no study of adult women who presented CD as adolescents, but who did not progress to ASPD. (III) Past studies have typically excluded CD participants with comorbid disorders (making them unrepresentative of clinical cases) or failed to take account of these disorders when examining neural correlates of ASB. (IV) No study has taken account of childhood maltreatment. (IV) There has been no study of associations of brain connectivity and subsyndromal psychopathic traits in females. Method: Three groups of young adult women, aged on average 24 years, completed clinical assessments and magnetic resonance imaging: women who consulted for substance misuse as adolescents and who were enrolled in a longitudinal study (n=44), sisters of ex-clients also enrolled in the longitudinal study (n=31), and newly recruited healthy women (n=24). Clinical data (diagnoses, psychopathic traits and other measures) from past waves and the current wave of data collection were used to characterize participants. Measures of brain structural connectivity (integrity of white matter tracts connecting specific regions) and functional connectivity (correlated resting-state activity between regions and Graph Theory topology) were investigated in four studies. Results: The women who had presented CD in adolescence presented high levels of lifetime comorbid anxiety and depression disorders, alcohol and drug dependence, childhood maltreatment, higher levels of psychopathic traits than in the general population, and poor psychosocial functioning and more aggressive behavior than the healthy women. Three main findings emerged: (1) CD prior to age 15 was associated with abnormalities of white matter integrity in adulthood despite low rates of progression to ASPD (Study I and II). These abnormalities were similar to those reported in previous studies featuring male or mixed-sex samples with CD and/or ASPD. (2) Most of the differences in white matter integrity between young adult women with a history of CD and healthy peers were explained by comorbid lifetime mental disorders and maltreatment (Study I and II). (3) Psychopathic traits were associated with unique structural and functional connectivity abnormalities (Study III and IV). Conclusions: We show for the first time that young women who presented CD as adolescents were characterized by structural connectivity abnormalities, despite not presenting ASPD but showing several indices of ASB. Even subsyndromal psychopathic traits presented by these women had unique connectivity correlates. Our findings emphasize the importance of treating CD in adolescence, as well as the comorbid mental disorders, and assessing and stopping maltreatment, so as to ensure a healthy transition to adulthood. Future studies investigating the neural correlates of CD, ASB in general, and psychopathic traits, need to take account of comorbid disorders and maltreatment

Do informal caregivers of people with dementia mirror the cognitive deficits of their demented patients?:A pilot study

Recent research suggests that informal caregivers of people with dementia (ICs) experience more cognitive deficits than noncaregivers. The reason for this is not yet clear. Objective: to test the hypothesis that ICs ‘mirror' the cognitive deficits of the demented people they care for. Participants and methods: 105 adult ICs were asked to complete three neuropsychological tests: letter fluency, category fluency, and the logical memory test from the WMS-III. The ICs were grouped according to the diagnosis of their demented patients. One-sample ttests were conducted to investigate if the standardized mean scores (t-scores) of the ICs were different from normative data. A Bonferroni correction was used to correct for multiple comparisons. Results: 82 ICs cared for people with Alzheimer's dementia and 23 ICs cared for people with vascular dementia. Mean letter fluency score of the ICs of people with Alzheimer's dementia was significantly lower than the normative mean letter fluency score, p = .002. The other tests yielded no significant results. Conclusion: our data shows that ICs of Alzheimer patients have cognitive deficits on the letter fluency test. This test primarily measures executive functioning and it has been found to be sensitive to mild cognitive impairment in recent research. Our data tentatively suggests that ICs who care for Alzheimer patients also show signs of cognitive impairment but that it is too early to tell if this is cause for concern or not

Neurocognitive networks for social cognition: Insights from diffusion weighted imaging and frontotemporal dementia

Empathy is a complex and multicomponent social cognitive function. It is underpinned by large-scale neurocognitive networks, the precise cognitive and neural structure of which remains debated. Despite this, relatively little work has considered the cognitive or neural components of empathy at the network-level. Here I present work using diffusion weighted magnetic resonance imaging (DWI) in healthy adults, and cognitive and behavioural assessment in a relatively rare form of dementia, the behavioural variant of frontotemporal dementia (bvFTD). Using these methods I explore: (a) the relationship between the microstructural properties of white matter tracts that mediate connectivity between distinct neurocognitive networks and separable cognitive components of empathic cognition (b) the cognitive and behavioural consequences of perturbation to neurocognitive networks in dementia. BvFTD is of interest here as it appears to preferentially target neural networks that support socioemotional processing. In chapters 2 and 3, evidence regarding the white matter structures that are affected by bvFTD guides investigations of the relationship between the microstructural properties of specific white matter tracts and social cognitive functioning in the healthy adult brain. In these chapters, I show that, in young healthy adults, two white matter pathways, sensitive to early changes in bvFTD, the Uncinate fasciculus (UF) and the cingulum bundle (CB), are related to individual differences in two components of empathic functioning, respectively: facial emotion decoding and mentalising. In chapter 4 I show the dissociation of performance on tasks assessing these cognitive functions in an individual with early bvFTD. I highlight the sensitivity and potential clinical utility of tasks assessing literary fiction-based mentalising. In Chapter 5 I present a detailed qualitative description of social cognitive change in frontotemporal dementia (FTD), from the perspective of family members. I consider what such detailed descriptions of everyday behaviour may tell us about the cognitive underpinnings of complex social behaviour. The findings of this thesis further our understanding of the dissociable neurocognitive networks that support empathic functioning, including their structural underpinnings and the behavioural consequences of their perturbation. In the general discussion, I consider the implications of this work for our understanding of social cognitive functioning and bvFTD

Diffusion weighted magnetic resonance imaging : validation, correction and applications

Diffusion weighted Magnetic Resonance Imaging (DW-MRI) images the structure of the white substance in the brains and connections between various brain parts. To validate this technique a test object (phantom) was developed, the structure of which resembles the structure of the white substance. This phantom was brought on the market and by now over 15 universities and hospitals own one. Furthermore, DW-MRI was applied to a patient with Landau-Kleffner syndrome. This syndrome involves losing the ability of using and understanding language as a consequence of epilepsy. Intensive therapy can restore the language ability. Important connections for language processing look different in these patients and the brains use more visual information in communication. The dissertation also describes further studies with a blindsight patient. In these patients the eyes still function, but the visual information is no longer consciously processed. And yet, the deep brain parts that unconsciously process emotions and visual information appear active. The necessary brain connections were shown in this patient and they were not present in control persons. Therefore, the patient has created new connections

Intégration de l'imagerie par résonance magnétique fonctionnelle (IRMf) à la tractographie pour cartographier les réseaux corticaux impliqués dans la dénomination d'images

Thèse de doctorat présenté en vue de l'obtention du doctorat en psychologie - recherche intervention, option neuropsychologie clinique (Ph.D)Il est de plus en plus communément admis que la plupart des fonctions cognitives chez l’humain sont organisées sous forme de réseaux cérébraux distribués plutôt que strictement sous forme de modules anatomiques ségrégués et localisés. Parmi ces fonctions cognitives, nos capacités à nommer des objets ou à formuler des idées sont fondamentales dans la communication verbale et une perturbation de ces capacités peut mener à des limitations significatives au quotidien (ex. manque de fluidité, discours vide de sens, paraphasies et difficultés à se faire comprendre). La combinaison multimodale des données en imagerie par résonance magnétique (IRM) est une façon d’étudier ces réseaux cérébraux. Elle permet d’investiguer simultanément plusieurs pans de l’architecture neurobiologique qui forme ces réseaux cérébraux (ex. les dynamiques fonctionnelles qu’entretiennent les différentes aires cérébrales et leurs connexions anatomiques sous-jacentes). L’intégration de l’IRM fonctionnelle (IRMf) pour guider la tractographie représente une combinaison multimodale pertinente pour étudier le réseau fonctionnel (aires cérébrales) et structurel (fibre de matière blanche) qui permet la dénomination d’images chez l’humain. Néanmoins, la combinaison de ces modalités est complexe et il n’existe à ce jour aucune documentation strictement dédiée à l’intégration l’IRMf pour guider la tractographie (ex. procédurier, bonnes pratiques, etc.). Le premier objectif de cette thèse consistait donc à effectuer une synthèse intégrative des aspects méthodologiques associés à l’intégration de l’IRMf pour guider la tractographie via une étude de la portée (article/étude #1). Nos résultats sont organisés en 19 constats qui concernent les défis méthodologiques associés à cette méthode de combinaison multimodale. Nous y proposons également des recommandations, des pistes de solution et avons identifié des lacunes dans les connaissances associées à cette méthodologie. Le second objectif de cette thèse visait à cartographier le réseau cérébral impliqué dans la dénomination d’images en intégrant l’IRMf pour guider la tractographie auprès de jeunes adultes en santé (article/étude #2). En appliquant les connaissances de l’article/étude #1 dans le cadre d’une étude empirique, nous avons pu proposer un modèle neurocognitif de la dénomination d’images. Dans ce modèle, nous validons la présence d’une voie ventrale et dorsale du traitement de l’information. Les résultats suggèrent aussi que les parties postérieures du cortex inférotemporal et du gyrus temporal supérieur peuvent servir d’interface entre ces deux voies du traitement de l’information. Cette étude appuie également la suggestion d'une voie ventrale indirecte qui transige par le lobe temporal antérieur. Finalement, cette thèse propose un outil fort utile pour les chercheurs qui désirent utiliser cette méthode intégrative, avancer les connaissances ou encore développer de nouveaux outils méthodologiques. Grâce à a l’intégration de l’IRMf pour guider la tractographie et la triangulation des données issues d’autres méthodes, cette thèse offre une analyse détaillée des processus cognitifs et des bases neurobiologiques impliqués dans la dénomination d’images. Il s’agit encore ici d’un outil très pertinent pour tous les cliniciens qui ont recours à la dénomination d’images dans le cadre de leur pratique.It has become more and more consensual that most cognitive functions in humans are organized in distributed brain networks rather than simply segregated and localized modules. Amongst these cognitive functions, our ability to name objects and elaborate ideas is fundamental for verbal communication as naming impairments can lead to significant limitations (i.e., lack of fluidity, empty speech, paraphasias and struggles to be understood). Multimodal magnetic resonance imaging (MRI) data combination provide opportunities for studying brain networks. It allows us to simultaneously investigate different aspects of the neurobiological architecture that forms brain networks (i.e., the functional dynamics that brain areas maintain together and their underlying anatomical connections). The integration of functional MRI (fMRI) to guide diffusion MRI (dMRI) tractography therefore represents an interesting way of combining multimodal MRI to study functional networks (brain areas) and white matter structures that allow picture naming abilities in humans. However, combining different MRI modalities remains a complex challenge and, up to this date, there is no documentation strictly dedicated to the integration of fMRI to guide dMRI tractography (i.e. bests practices, step-by-step guide, recommendations, etc.). The first objective of this thesis was to provide an integrative synthesis of the methodological aspects related to the integration of fMRI to guide dMRI tractography through a scoping review (article/study #1). Our results are organized in 19 findings which concern the methodological challenges associated with this multimodal combination technique. We there offer recommendations, solutions and identify gaps in the literature. The second objective of this thesis was to map the brain network involved in picture naming by integrating fMRI to guide dMRI tractography in healthy young adults (article/study #2). By applying the knowledge obtained from article/study #1 in the context of an experimental study, we were able to propose a neurocognitive model of picture naming. In this model, we confirm the presence of a ventral and dorsal information processing pathway. Our results also suggest that the posterior parts of the inferotemporal cortex and superior temporal gyrus may serve as an interface between these two information processing pathways. This study also supports the hypothesis of an indirect ventral pathway that relays through the anterior temporal lobe. Finally, this thesis offers a useful tool for researchers who wish to use this multimodal integrative method, advance knowledge or develop new methodological tools. Thanks to the integration of fMRI to guide dMRI tractography and the triangulation of data from other methods, this thesis was able to offer a complex and comprehensive look at the cognitive processes and neurobiological basis involved in picture naming. Again, this is also a very relevant tool for all clinicians who use picture naming in their everyday practice