Dissertations / Theses on the topic 'Brain's default mode'

It is now widely accepted that cognitive control depends on the integrated operation of large-scale distributed brain networks. Recent methodological advances allow both structural and functional connectivity (FC) within these networks to be studied non- invasively in vivo. These approaches hold the promise of dramatically extending our understanding of the impact of traumatic brain injury (TBI) on cognitive control, which has the potential to help determine strategic targets for the rehabilitation of individuals with TBI. In the current thesis, structural and functional magnetic resonance imaging is combined to test the general hypothesis that cognitive deficits after TBI arise from functional disconnection within brain networks that mediate cognitive functions. Of particular interest are the interactions between two brain networks known as the Salience Network (SN) and the Default Mode Network (DMN). These networks are thought to be important for cognitive control however, how these networks interact during cognitive control is limited. This thesis largely investigates the effect of TBI on network interactions that accompany changing motor control. Functional MRI of the Stop Signal Task (SST) is initially used to study response inhibition. In healthy subjects, FC between the right anterior insula (rAI), a key node of the SN, and the DMN transiently increased during stopping. This change in FC was not seen in a group of TBI patients with impaired cognitive control. Furthermore, the amount of damage to the underlying white matter tract negatively correlated with the strength of FC between the networks. These findings are confirmed in a second group of TBI patients. In the second group, switching rather than inhibiting a motor response: (1) was accompanied by a similar increase in network FC in healthy controls; (2) was not seen in TBI patients; and (3) tract damage after TBI again correlated with FC breakdown. I also replicate this pattern of structure-function in a group of elderly participants who demonstrate similar cognitive control impairments as the TBI group. The findings show that FC between the rAI and DMN increases with cognitive control, and that the ability to efficiently regulate the FC between the rAI and DMN can be predicted by the structural integrity within a remote brain network previously proposed to be involved in switching between internally and externally directed attention. This work provides evidence for a model of cognitive control where the SN is involved in the attentional capture of salient external stimuli and signals the DMN to reduce its activity when attention is externally focused. It also identifies DMN dysfunction as underlying various cognitive deficits after TBI, and confirms the relevance of white matter damage in the development of brain dysfunctions after TBI.

The default mode network (DMN) is a system of brain regions observed on functional magnetic resonance imaging (fMRI) when an individual is resting and deactivated during performance of goal-directed cognitive tasks, and is thought to be involved in self-related information processing. While differences with age have been observed in anatomical and functional connectivity, resting activity, and task-related deactivation of the DMN, age-related differences in the interaction between resting connectivity and active processing in the DMN are not well understood. In this study, the relation between functional connectivity and cognitive activation during performance of a task known to involve key DMN regions (i.e., posterior cingulate, medial frontal, medial temporal, and parietal regions) was investigated. Statistical Parametric Mapping (SPM) was performed on fMRI scans in healthy young (n=11) and older (n=19) adults to assess functional connectivity of the DMN at rest, and activation during a self-related source memory task. Older adults were then divided based on task performance into high- and low-performing groups to assess individual differences in connectivity and activation. Though both young and older adults showed robust connectivity among DMN regions, older adults showed greater connectivity between the DMN and other areas, particularly in frontal regions; this expansion was especially evident in low performers. Activation of the DMN during encoding and retrieval of self-related versus other-related information was greater in young adults than older adults. While low-performing older adults showed no differences between self- and other-related activation at retrieval, high performers engaged regions outside the DMN during other-related retrieval. These results suggest that older adults whose self-related source memory performance is similar to young adults exhibit preservation of DMN connectivity, self-related activation in the DMN which more closely resembles that of young adults, and additional recruitment of non-DMN networks to achieve higher memory performance. Aging in low performers is associated with dedifferentiation of DMN connectivity with expansion particularly into frontal regions, and reduced ability to engage the DMN or other networks in discriminating self- from non-self-related information. Further, preservation of DMN-specific functional connectivity is directly related to greater activation differences during retrieval of self-related versus non-self-related information in older adults.

Individuals with mild cognitive impairment (MCI) show variable impairment in autobiographical memory function, source memory function and reduced integrity in the brain’s default mode network (DMN). There is overlap between the DMN, such as the medial posterior cortical hub, and brain regions that are active when participants recall autobiographical memories. To assess the association between autobiographical memory and the DMN, 14 MCI and eleven age and education-matched healthy control participants were assessed using the autobiographical memory interview (AMI) and underwent resting state fMRI scans. The same participants underwent a test of source memory which assessed both recognition and source memory. The MCI group showed significantly increased semantic as well episodic memory impairments using the AMI, evident across the lifespan for episodic memory but not for childhood semantic memory. Significantly poorer DMN connectivity, using a goodness of fit index (GOF) of the DMN template, was evident in the MCI group. MCI participants showed poorer performance on both recognition and source memory relative to HC participants. A modest association between AMI semantic memory (r=0.4) scores, but not episodic memory scores (r=0.09), and DMN connectivity was found in these participants. For future study the predictive value of MR imaging in the DMN of MCI participants should be explored.

Individuals with Parkinson’s disease (PD) often show cognitive impairments in addition to motor symptoms, with the majority of PD patients converting to dementia as the disease progresses. The changes in the microstructural integrity of key nodes in resting state networks (RSNs) could be a good indicator of the cognitive effects of PD on brain regions as it progresses to dementia. To assess the association between cognitive effects and microstructural change, the microstructural integrity of the regions of interest (ROIs) in 4 resting state networks (RSN), specifically the default mode network (DMN), based on DTI were obtained in three separate groups of patients with PD. One group of patients (PD-N) were cognitively normal, while the second group of patients (PD-MCI) reflect the transitional phase of mild cognitive impairment prior to dementia, and the third group of patients (PD-D) possessed a clear diagnosis of dementia. A comparison group of healthy controls (HC) were included, matched across the three patient groups. The PD-D group showed worse microstructural integrity for the majority of the ROIs across the 4 networks. The loss of structural integrity in the PD-MCI group was more selective, with some ROIs showing similar changes to PD-D, and others showing similar changes to the PD-N group. The PD-N group fail to show any changes in the structural integrity of any ROIs, relative to HC. For future study, a combined structural / functional study should be performed to examine if there are similar changes across both measures.

Abstract: The default mode network of the brain is a set of functionally connected regions associated with introspection and daydreaming. Recent fMRI studies have discovered that the default mode network is often perturbed in the diseased brain. For example, the default mode network is known to be modulated in dementia, ADHD, depression, and schizophrenia, among others. This has led many into believing that this network could have a role in the physiopathology of nervous system disease, or could be a useful marker of brain function. However, very few studies have yet been done which investigate how surgical lesions such as brain tumours affect the default mode network. Consequently, the goal of this project was to characterise the effect of brain tumours on the default mode network based on their location, histological type, and other parameters.
Le mode de fonctionement par défaut du cerveau est un réseau cérébral associé à la rêverie et à l’introspection. Des études récentes sur ce réseau ont découvert qu’il est perturbé dans plusieurs pathologies cérébrales. Par example, le mode de fonctionnement par défaut est modulé en démence, TDAH, dépression, schizophrénie et plusieurs autres maladies liés au cerveau. Ceci a mené à l’hypothèse que le mode de fonctionnement par défaut pourrait avoir un rôle dans la physiopathologie des maladies du système nerveux, ou pourrait être un marqueur utile du fonctionnement cérébral. Par contre, très peu d’études ont investigué l’effet de lésions chirurgicaux comme les tumeurs cérébrales sur le mode de fonctionnement par défaut. Par conséquent, le but de ce projet était de caractériser l’importance de l’histologie, de la localisation et de plusieurs autres paramètres de l’effet d’une tumeur cérébrale sur le mode de fonctionnement par défaut.

The Default Mode Network (DMN) is a large-scale brain network implicated in the control and monitoring of internal modes of cognition. The aim of this research was to investigate DMN function and its relationship to other large-scale cognitive control networks through functional connectivity analysis and analysis of combined electroencephalographic (EEG) recordings. Data utilised across a series of three experiments were obtained from combined EEG-functional Magnetic Resonance Imaging recordings acquired during technical development of a new scanner in the Clinical Research Centre, Ninewells Hospital, Dundee. Analyses were based on data acquired from neurologically healthy participants while they rested with their eyes-closed for five minutes. Following this, participants completed a 14-minute auditory attention task, designed to engage the dorsal and ventral attention networks. In this task, participants responded to task-relevant stimuli (odd/even numbers) and attempted to inhibit their responses to task-irrelevant ‘oddballs’ (the number ‘0’) and task-irrelevant/distractor stimuli (environment sounds). Experiment 1 utilised the simultaneous acquired EEG-fMRI resting-state data in order to establish whether EEG frequency content in the beta range (13-30 Hz) was a significant predictor of DMN activity (regions of which were identified on an individual basis using functional connectivity analysis). Results were comparable to existing literature showing there is inconsistency in establishing a reliable electrophysiological signature of the DMN. Experiment 1 also employed region-of-interest (ROI)-to-ROI functional connectivity analysis as a method of exploring the functional relationship between the DMN and: (1) a task-positive resting-state network; (2) other commonly identified DMN regions; and (3) regions covering the whole of the cerebral cortex. Results revealed networks were correlated at a component-based level and challenged existing literature which appears to over-generalise results from exploration of network interaction. Findings also revealed activation of specific DMN components were coupled with down-regulation of sensory-associated cortical regions. Experiment 2 analysed the fMRI data that were obtained from the auditory attention task in order to: (1) determine whether DMN activity was observed when participants were engaged in an externally-directed task; and (2) explore changes in DMN activity associated with increasing task duration. Results revealed that activation of the DMN was prominent and did not vary over three equal time periods. This supports existing research showing the DMN is a continuously active system (whose activity is modulated based on external-task demands). Results also hinted at the existence of possible relationships between the DMN and components of several other large-scale control networks. Therefore, in Experiment 3 potential interactions were explored using ROI-to-ROI functional connectivity analysis of the whole 14-minute time series. Firstly, functional connectivity within the dorsal/ventral attention, executive/frontoparietal control and salience networks was analysed; secondly, the relationships between putative regions of these networks and the DMN were analysed. Overall, results revealed that networks were functionally connected with one another at a component-based level only. This suggests flexible interaction between several large-scale control networks allows neurologically healthy participants to allocate resources to the simultaneous monitoring of the internal and external worlds.

This study investigated the effects of lesion presence within larger brain networks (e.g., default mode network (DMN), salience network (SN), and mentalizing network (MN)) in the chronic phase of a pediatric traumatic brain injury (TBI) and the effect on social function. We compared children with a TBI to children with an orthopedic injury (OI) with three different aims. The first aim was to determine whether network volume differed by group (e.g., TBI vs. OI). Second, investigate if lesion presence in a sub component region of the network resulted in total network volume loss for that network. Finally, learn whether network volume would predict outcome on the Behavior Assessment System for Children, Second Edition (BASC-2). Approximately 184 participants (65% male; 70% Caucasian) between the ages of 6-17 years completed testing and a structural MRI scan in the chronic stage (at least one-year post-injury) of the injury. Injury severity included complicated mild, moderate, and severe TBI. Radiological findings were analyzed using recommendations from the Common Data Elements' core (presence or absence of a lesion) and supplementary (lesion type and location) recommendations. Volumetrics for all participants were obtained with FreeSurfer to quantify total network volumes for the DMN, SN, and MN. The parent of each participant completed a behavioral measure for externalizing and internalizing behaviors. Three sets of statistical analyses were completed, including multivariate analysis of covariance, analysis of covariance, and multiple regression, for each of the three aims of the study, respectively. There were significant differences in total DMN volume between the two groups and participants with lesions solely in the MN had lower total MN volume. Moreover, lower total MN volume was associated with worse functioning on measures of externalizing and internalizing behaviors. The larger implications, including developmental and social implications, of these findings are discussed.

Les mutations génétiques et les conditions pathologiques affectent la connectivité functionnelle du cerveau. Nous avons combiné la mutagénèse chez la souris et l’analyse de connectivité fonctionnelle (CF) par imagerie en Resonance Magnétique Nucléaire (IRM) pour déterminer l’impact de la délétion du gène codant pour le récepteur orphelin GPR88 sur la CF du cerveau entier. En utilisant une approche non biaisée, nous avons découvert que la délétion génétique chez la souris altère fortement le Default Mode Network, une caractéristique de nombreuses maladies psychiatriques. Nous avons aussi observé des modifications importantes de la connectivité des cortex moteurs et somatosensoriels,et du striatum en accord avec le pattern d’expression du récepteur. Enfin, une analyse par régions d’intérêt montre une perturbation importante du réseau mesocorticolimbic, qui pourrait expliquer la tendance de ces animaux à consommer de fortes quantités d’alcool. La concordance entre les altérations de CF et celles du comportement des animaux GPR88 knockout positionnent ce récepteur comme une cible prometteuse pour le traitement de maladies psychiatriques
Pathological agitations of the brain and the expression or mutation of single gene affect overall brain connectivity. Here we combined mouse mutagenesis with functional and structural MRI and explored mouse whole brain connectivity maps non-invasively in response to the inactivation of Gpr88 gene. We perceived robust modifications in the default mode network which is considered a hallmark of many psychiatric conditions, followed by sensori-motor network allied to sensorimotor gating deficiency underlying hyperactivity phenotype in Gpr88-/- mice. In addition, hippocampal and dorsal striatum functional connectivity perturbations might underlie learning deficiency and weakened amygdala connectivity with cortex and striatum might suggest triggering of risk-taking behavior previously observed in these animals. Moreover, Gpr88 deletion strongly modifies the reward network leading Gpr88-/- mice vulnerable to alcohol intake. This is the first evidence of Gpr88 involvement in reshaping the mouse brain connectome. The concordance between connectivity alterations and behavior deficits posits Gpr88 as a potential target for psychiatric disorders

Resting state functional magnetic resonance imaging (fMRI) is currently at the forefront of research on cognition and the brain’s large-scale organization. Patterns of hemodynamic activity that it records have been strongly linked to certain behaviors and cognitive pathologies. These signals are widely assumed to reflect local neuronal activity but our understanding of the exact relationship between them remains incomplete. Researchers often address this using multimodal approaches, pairing fMRI signals with known measures of neuronal activity such as electroencephalography (EEG). It has long been thought that infraslow (< 0.1 Hz) fMRI signals, which have become so important to the study of brain function, might have a direct electrophysiological counterpart. If true, EEG could be positioned as a low-cost alternative to fMRI when fMRI is impractical and therefore could also become much more influential in the study of functional brain networks. Previous works have produced indirect support for the fMRI-EEG relationship, but until recently the hypothesized link between them had not been tested in resting humans. The objective of this study was to investigate and characterize their relationship by simultaneously recording infraslow fMRI and EEG signals in resting human adults. We present evidence strongly supporting their link by demonstrating significant stationary and dynamic correlations between the two signal types. Moreover, functional brain networks appear to be a fundamental unit of this coupling. We conclude that infraslow electrophysiology is likely playing an important role in the dynamic configuration of the resting state brain networks that are well-known to fMRI research. Our results provide new insights into the neuronal underpinnings of hemodynamic activity and a foundational point on which the use of infraslow EEG in functional connectivity studies can be based.

Abstract Neuropsychiatric illnesses usually become overtly manifest in adolescence and early adulthood. A critical long-term aim is to be able to prevent the development of such illnesses, which requires instruments to identify subjects at high risk of illness and to offer them effective interventions. There is an indisputable need for more sophisticated methods to enable more precise detection of adolescents and young adults who are at high risk of developing psychosis. Abnormal function in brain networks has been reported in people with schizophrenia and other psychotic disorders. Similar abnormalities have been found also in people at risk for developing psychosis, but it is not known whether this applies also to spontaneous resting state activity in young people with a familial risk for psychosis. We conducted resting-state functional MRI (R-fMRI) in 72 (29 male) young adults with a history of psychosis in one or both parents (FR) but without psychosis themselves, and 72 (29 male) similarly healthy control subjects without familial risk for psychosis. Both groups in the Oulu Brain and Mind study were drawn from the Northern Finland Birth Cohort 1986. All volunteers were 20–25 years old. Parental psychosis was established using the Care Register for Health Care. R-fMRI data was pre-processed using independent component analysis (ICA). A dual regression technique was used to detect between-group differences with p < 0.05 threshold corrected for multiple comparisons at voxel level. FR subjects demonstrated significantly decreased activity compared to control subjects in the default mode network and in the central executive network and increased activity in the cerebellum. The findings clarify previously controversial literature on the subject. The finding suggests that abnormal activity in these brain networks in rest may be associated with increased vulnerability to psychosis. The findings maybe helpful in developing more precise methods for detecting young people at highest risk for developing psychosis
Tiivistelmä Psykoottisiin häiriöihin sairastutaan yleensä nuoruudessa tai varhaisaikuisuudessa. Psykoositutkimuksen tavoitteena on löytää uusia menetelmiä, joiden avulla kyettäisiin tunnistamaan suurimmassa psykoosiriskissä olevat nuoret, jotta heille voitaisiin tarjota sairautta ennaltaehkäiseviä hoitokeinoja. Skitsofreniaan ja muihin psykoottisiin häiriöihin sairastuneilla on havaittu aivotoiminnan poikkeavuuksia. Samankaltaisia aivotoiminnan poikkeavuuksia on havaittu myös nuorilla, jotka ovat vaarassa sairastua psykoosiin. Toistaiseksi on ollut epäselvää, onko psykoosiin sairastuneiden henkilöiden lapsilla aivohermoverkkojen toiminnan poikkeavuuksia lepotilassa. Suoritimme aivojen lepotilan MRI-tutkimuksen (R-fMRI) 72:lle (29 miestä) nuorelle aikuiselle, joiden jompikumpi vanhempi oli sairastunut psykoosin sekä 72:lle (29 miestä) nuorelle aikuiselle, joiden vanhemmat eivät olleet sairastaneet psykoosia. Molemmat tutkimusryhmät tässä Oulu Brain and Mind -tutkimuksessa olivat Pohjois-Suomen 1986 syntymäkohortin jäseniä. Tutkittavat olivat 20–25 vuoden iässä. Lepotilan toiminnallinen magneettikuvaus suoritettiin 1.5 Teslan Siemensin magneettikuvantamislaitteella. Tutkimuskohteiksi valittiin lepotilan toiminnallinen aivohermoverkko, toiminnan ohjauksesta vastaava aivohermoverkko ja pikkuaivot. Kuvantamisdataan sovellettiin itsenäisten komponenttien analyysia aivohermoverkkojen määrittämistä varten. Ryhmien välisen eron havaitsemiseen käytettiin ei-parametristä permutaatiotestiä, joka kynnystettiin tilastollisesti merkitsevään tasoon (p < 0.05). Lepotilan oletushermoverkossa ja toiminnanohjauksesta vastaavassa aivohermoverkoissa havaittiin vähäisempää aktiivisuutta ja pikkuaivoissa kohonnutta aktiivisuutta perinnöllisessä psykoosiriskissä olevilla nuorilla aikuisilla verrattuna verrokkeihin. Tutkimustulokset selkeyttivät aiempaa ristiriitaista kirjallisuutta tutkimusaiheesta. Tutkimuksessa havaittujen aivoalueiden poikkeava toiminta lepotilassa voi liittyä kohonneeseen psykoosin puhkeamisriskiin. Tutkimuslöydösten avulla voidaan todennäköisesti edesauttaa parempien kuvantamismenetelmien kehittämistä suurimmassa psykoosiriskissä olevien nuorten tunnistamiseen

While task-based functional magnetic resonance imaging (fMRI) has helped us understand the functional role of many regions in the human brain, many diseases and complex behaviors defy explanation. Alternatively, if no task is performed, the fMRI signal between distant, anatomically connected, brain regions is similar over time. These correlations in “resting state” fMRI have been strongly linked to behavior and disease. Previous work primarily calculated correlation in entire fMRI runs of six minutes or more, making understanding the neural underpinnings of these fluctuations difficult. Recently, coordinated dynamic activity on shorter time scales has been observed in resting state fMRI: correlation calculated in comparatively short sliding windows and quasi-periodic (periodic but not constantly active) spatiotemporal patterns. However, little relevance to behavior or underlying neural activity has been demonstrated. This dissertation addresses this problem, first by using 12.3 second windows to demonstrate a behavior-fMRI relationship previously only observed in entire fMRI runs. Second, simultaneous recording of fMRI and electrical signals from the brains of anesthetized rats is used to demonstrate that both types of dynamic activity have strong correlates in electrophysiology. Very slow neural signals correspond to the quasi-periodic patterns, supporting the idea that low-frequency activity organizes large scale information transfer in the brain. This work both validates the use of dynamic analysis of resting state fMRI, and provides a starting point for the investigation of the systemic basis of many neuropsychiatric diseases.

博士
國立陽明大學
生物醫學影像暨放射科學系
104
The human brain is one of the most complex systems in nature. Using non-invasive functional magnetic resonance imaging (fMRI) technology, researchers can explore the structural and functional brain networks on large scale. In human study, the default mode network (DMN) has been suggested to support a variety of self-referential functions, including recollection and imagination, conceptual processing, and autobiographical memory. Various neurological and psychiatric disorders including schizophrenia, Alzheimer’s disease, autism, and addiction have been demonstrated that linked to DMN dysregulation. The default mode network (DMN) has been suggested to support a variety of self-referential functions in humans. The human DMN has been fractionated into subsystems based on their distinct responses to cognitive tasks and functional connectivity architecture, which might reflect functional hierarchy and segregation within the network. Since preclinical models can be used in translational studies of neuropsychiatric disorders, partitioning of DMN in nonhuman species may inform both physiology and pathophysiology of the human DMN. In this study, we investigate constituents of the rat DMN using resting-state functional MRI (rs-fMRI) and diffusion tensor imaging (DTI). The DMN was identified using a group-level independent component analysis on the rs-fMRI data. Using modularity analyses, the rat DMN was fractionated into an anterior and a posterior subsystem, which were further segregated into five modules. Fiber density derived from DTI tractography demonstrates a close relationship with the functional connectivity between DMN regions, and provided anatomical evidence to support the detected DMN functional sub-systems. We also observed distinct modulation within and between these DMN subcomponents following acute sensorimotor stimulation and aged- related cognitive dysfunction, consistent with findings in the human DMN. Together, these results suggest that the rat DMN, like the analogous human DMN, can be partitioned into several subcomponents that may be associated with distinct functions. Further investigation into the neurobiological implications of the DMN organization in both healthy and pathological preclinical models is warranted. In summary, our work provides the architecture of rat DMN using modularity analysis of re-sfMRI data and associated this with the underlying structural connectivity obtained with diffusion tensor imaging (DTI) tractography. Together, our findings on the rat DMN and its organization provide a platform to explore the physiological basis and behavioral functions of this prominent, large-scale network.

碩士
國立臺灣科技大學
電子工程系
102
Resting state networks which relate to the alterations of coherent intrinsic neuronal activity based on blood oxygen level-dependent (BOLD) fluctuations can be observed in the resting state functional magnetic resonance imaging (rsfMRI). Among all resting state networks, default mode network (DMN) has been shown to exhibit reduced activation in the presence of high cognitive demand and has been used to investigate the neuronal dysfunctions. Recently, there are several studies showing that functional activity can be related to the baseline metabolic levels, such as glutamate, glutamine and GABA. In our research, we combine rsfMRI and MRS to find the revelation between the intensity of DMN and the concentration of brain metabolites especially Glx (glutamate+glutamine). We use proton echo planar spectroscopy imaging (PEPSI), as a fast magnetic resonance spectroscopic imaging (MRSI) method, is able to acquire the distribution of brain metabolites with acceptable reproducibility in the medial wall. Combining with echo planar imaging (EPI) and find the subject’s DMN component by individual (iICA) and group (gICA) individual component analysis. The results of regression successfully shows that Glx has positive correlation with DMN intensity in precuneus and anterior cingulate cortex which are the region in DMN, and the results of iICA and gICA have no significant different.

碩士
國立陽明大學
腦科學研究所
98
Objective: Dysmenorrhea is a common painful disorder with fluctuation according to menstrual cycle in women during productive age. Recent studies of chronic pain have showed altered cortical activity unrelated to pain, but the correlations between the structural impairments and psychological or cognitive dysfunctions are not clearly known. Here we propose that primary dysmenorrhea causes not only abnormal responses to stimuli due to altered central representation, but also harms the default-mode network (DMN), a functional connectivity of cortical regions known to be active at rest. Methods: Resting state fMRI scanning were performed in 17 primary dysmenorrhea (PDM) patients and 15 matched healthy women. Independent component analysis was used to dissect their functional connectivity. The DMN was chose according to the template and was compared between two groups. Results: No significant changes in functional connectivities were noted across menstrual cycle. But PDM showed increased functional connectivity to DMN in left lateral globus pallidus, right superior frontal gyrus, cuneus, middle frontal gyrus, insula, precentral gyrus, middle temporal gyrus, and superior temporal gyrus. Conclusion: Functional connectivity might not be influence across menstrual cycle. Like other chronic pain studies, dysmenorrhea indeed changes the functional connectivity to DMN. This might be due to long-term cyclic pain stimulation.

BACKGROUND: Schizophrenia manifests as a constellation of both psychotic symptoms (eg. hallucinations, delusions) and so-called negative symptoms. The latter includes anhedonia, avolition, amotivation and they are the strongest predictors of disability. Resting state fMRI (rsfMRI) has demonstrated that the brain is organized into low-dimensional number (7-17) brain networks and this allowed visualization of the relationship between symptom severity and large-scale brain network organization. Traditional rsfMRI analyses have assumed that the spatial organization of these networks are spatially invariant between individuals. This dogma has recently been overturned with the observation that the spatial organization of these brain networks shows significant variation between individuals. We sought to determine if previously observed relationships between symptom severity and network connectivity are actually due to individual differences in spatial organization. METHODS: 44 participants diagnosed with schizophrenia underwent rsfMRI scans and clinical assessment. A multivariate pattern analysis was used to examine how each participant’s whole brain functional connectivity correlates with ‘negative’ symptom severity. RESULTS: Brain connectivity to a region of the right dorso-lateral pre-frontal cortex (r DLPFC) correlates with symptom severity. The result is explained by the individual differences in the topographic distribution of two brain networks: the default mode network (DMN) and the task positive network (TPN). Both networks demonstrate strong (r~0.49) and significant (p<0.001) relationships between topography and symptom severity. For individuals with low symptom severity, this critical region is a part of the DMN. In highly symptomatic individuals, this region is a part of the TPN. CONCLUSIONS: Previously overlooked individual variation in brain organization is tightly linked to individual variation in schizophrenia symptom severity. The recognition of critical links between network topology and pathological symptomology may serve as a guide for future interventions aimed at establishing causal relationships between certain critical regions of the brain and cognitive and behavioral phenotypes. Thus, fMRI and network topology may be translated to a clinical setting as a viable, individual-centered treatment option.
2020-06-17T00:00:00Z

L’aphasie est un trouble acquis du langage entraînant des problèmes de communication pouvant toucher la compréhension et/ou l’expression. Lorsque l’aphasie fait suite à un accident vasculaire cérébral, une régression des déficits communicatifs s'observe initialement, mais elle peut demeurer sévère pour certains et est considérée chronique après un an. Par ailleurs, l’aphasie peut aussi être observée dans l’aphasie progressive primaire, une maladie dégénérative affectant uniquement le langage dans les premières années. Un nombre grandissant d’études s’intéressent à l’impact de la thérapie dans l’aphasie chronique et ont démontré des améliorations langagières après plusieurs années. L’hémisphère gauche semble avoir un rôle crucial et est associé à de meilleures améliorations langagières, mais la compréhension des mécanismes de plasticité cérébrale est encore embryonnaire. Or, l’efficacité de la thérapie dans l’aphasie progressive primaire est peu étudiée. À l’aide de la résonance magnétique fonctionnelle, le but des présentes études consiste à examiner les mécanismes de plasticité cérébrale induits par la thérapie Semantic Feature Analysis auprès de dix personnes souffrant d’aphasie chronique et d’une personne souffrant d’aphasie progressive primaire. Les résultats suggèrent que le cerveau peut se réorganiser plusieurs années après une lésion cérébrale ainsi que dans une maladie dégénérative. Au niveau individuel, une meilleure amélioration langagière est associée au recrutement de l’hémisphère gauche ainsi qu’une concentration des activations. Les analyses de groupe mettent en évidence le recrutement du lobule pariétal inférieur gauche, alors que l’activation du gyrus précentral gauche prédit l’amélioration suite à la thérapie. D’autre part, les analyses de connectivité fonctionnelle ont permis d’identifier pour la première fois le réseau par défaut dans l’aphasie. Suite à la thérapie, l’intégration de ce réseau bien connu est comparable à celle des contrôles et les analyses de corrélation suggèrent que l’intégration du réseau par défaut a une valeur prédictive d’amélioration. Donc, les résultats de ces études appuient l’idée que l’hémisphère gauche a un rôle prépondérant dans la récupération de l’aphasie et fournissent des données probantes sur la neuroplasticité induite par une thérapie spécifique du langage dans l’aphasie. De plus, l’identification d’aires clés et de réseaux guideront de futures recherches afin d’éventuellement maximiser la récupération de l’aphasie et permettre de mieux prédire le pronostic.
Aphasia is an acquired language impairment leading to communication disorders which may affect comprehension and/or expression. When aphasia follows a stroke, major recovery of the communicative deficits is initially observed after the lesion, but for some the aphasia may remain severe and is considered to be chronic after a year. Furthermore aphasia can be observed in primary progressive aphasia, a degenerative disease only affecting language in the early years. The impact of therapy in chronic aphasia is the subject of growing literature in recent years and has shown language improvements after several years of therapy. The left hemisphere seems to have a crucial role and is associated with greater language improvements but our understanding of brain plasticity mechanisms is still lacking. In primary progressive aphasia, few studies have examined therapy effectiveness. Using functional magnetic resonance imaging, the aim of these studies was to examine therapy-induced brain plasticity mechanisms following Semantic Feature Analysis in ten participants suffering from chronic aphasia and one participant with primary progressive aphasia. The results suggest that brain reorganization is possible several years after injury and in degenerative disease. At the individual level, greater language improvement is associated with the recruitment of the left hemisphere and less activated areas. Group analysis shows the recruitment of left inferior parietal lobule, whereas the activation of left precentral gyrus predicts improved response to therapy. Functional connectivity analysis allowed for the first time the identification of the default-mode network in aphasia. Following therapy, the integration of this well-known network is comparable to that of the controls and the correlation analysis suggests that the default-mode network integration has a predictive value for improvement. Therefore, the results of these studies support the idea that the left hemisphere has a major role in the recovery of aphasia and provide evidence on therapy-induced neuroplasticity in aphasia. In addition, the identification of key areas and networks will guide future research in order to possibly maximize the recovery of aphasia and to better predict the prognosis.