Altered functional connectivity in the default mode network is associated with cognitive impairment and brain anatomical changes in Parkinson's disease.

To assess whether functional neural connectivity is disrupted between the regions of the default mode network (DMN) in Parkinson's disease (PD) and how this connectivity is related to cognition, brain gray matter structure and white matter integrity and diffusivity. Thirty-seven PD patients and 16 healthy controls were evaluated, using resting-state functional magnetic resonance imaging (MRI), T1-weighted MRI, diffusion-weighted imaging and a battery of cognitive tests. Functional connectivity between the regions of the DMN, specifically in the precuneus, anterior and posterior cingulate, medial prefrontal and temporal and inferior parietal cortices was assessed with seed-to-voxel connectivity; gray matter volume and white matter values were determined using voxel-based morphometry and tract-based spatial statistics. Reduced functional connectivity was observed between the posterior cingulate and medial temporal lobe in PD. Lower cognitive performance, gray matter loss in posterior, medial temporal and parietal areas, and fractional anisotropy reduction in the white matter adjacent to DMN regions were also observed in PD patients compared with healthy controls. Lower DMN functional connectivity correlated with lower verbal and visual memory and visual abilities performance in PD. In addition, lower DMN functional connectivity correlated with lower gray matter volume in the posterior cingulate and precuneus, and with lower white matter fractional anisotropy of the inferior longitudinal and posterior cingulate fasciculi in PD. By combining different neuroimaging techniques and cognitive data, results showed that functional connectivity alteration between the regions of the DMN is associated with lower cognitive performance and gray and white matter abnormalities in PD.

Lucas-Jiménez O ，Ojeda N ，Peña J ，Díez-Cirarda M ，Cabrera-Zubizarreta A ，Gómez-Esteban JC ，Gómez-Beldarrain MÁ ，Ibarretxe-Bilbao N ... -  《-》

Cognitive impairment and resting-state network connectivity in Parkinson's disease.

The purpose of this work was to evaluate changes in the connectivity patterns of a set of cognitively relevant, dynamically interrelated brain networks in association with cognitive deficits in Parkinson's disease (PD) using resting-state functional MRI. Sixty-five nondemented PD patients and 36 matched healthy controls were included. Thirty-four percent of PD patients were classified as having mild cognitive impairment (MCI) based on performance in attention/executive, visuospatial/visuoperceptual (VS/VP) and memory functions. A data-driven approach using independent component analysis (ICA) was used to identify the default-mode network (DMN), the dorsal attention network (DAN) and the bilateral frontoparietal networks (FPN), which were compared between groups using a dual-regression approach controlling for gray matter atrophy. Additional seed-based analyses using a priori defined regions of interest were used to characterize local changes in intranetwork and internetwork connectivity. Structural group comparisons through voxel-based morphometry and cortical thickness were additionally performed to assess associated gray matter atrophy. ICA results revealed reduced connectivity between the DAN and right frontoinsular regions in MCI patients, associated with worse performance in attention/executive functions. The DMN displayed increased connectivity with medial and lateral occipito-parietal regions in MCI patients, associated with worse VS/VP performance, and with occipital reductions in cortical thickness. In line with data-driven results, seed-based analyses mainly revealed reduced within-DAN, within-DMN and DAN-FPN connectivity, as well as loss of normal DAN-DMN anticorrelation in MCI patients. Our findings demonstrate differential connectivity changes affecting the networks evaluated, which we hypothesize to be related to the pathophysiological bases of different types of cognitive impairment in PD.

Baggio HC ，Segura B ，Sala-Llonch R ，Marti MJ ，Valldeoriola F ，Compta Y ，Tolosa E ，Junqué C ... -  《-》

Default mode network connectivity patterns associated with visual processing at different stages of Parkinson's disease.

Rektorova I ，Krajcovicova L ，Marecek R ，Novakova M ，Mikl M ... -  《-》

Gray and white matter imaging: A biomarker for cognitive impairment in early Parkinson's disease?

The aim of this work was to investigate the cortical and white matter changes that underlie cognitive impairment in patients with incident Parkinson's disease (PD) disease using voxel-based morphometry and diffusion tensor imaging. Newly diagnosed nondemented PD (n = 125) and control subjects (n = 50) were recruited from the Incidence of Cognitive Impairment in Cohorts with Longitudinal Evaluation in Parkinson's Disease Study and completed cognitive assessments and 3T structural and diffusion tensor MR imaging. Voxel-based morphometry was performed to investigate the relationship between gray matter volume and cognitive ability. Microstructural white matter changes were assessed with diffusion tensor imaging measures of fractional anisotropy and mean diffusivity using tract-based spatial statistics. Increased mean diffusivity was observed bilaterally in subjects with PD, relative to controls (P = 0.019). Increased mean diffusivity was associated with performance on the semantic fluency and Tower of London tasks in frontal and parietal white matter tracts, including the cingulum, superior longitudinal fasciculus, inferior longitudinal fasciculus, and inferior fronto-occipital fasciculus. There was no difference in total gray matter volume between groups; however, bilateral reductions in frontal and parietal gray matter volume were associated with reduced performance on measures of executive function in PD subjects. At the earliest stages of PD, regionally specific increases in central white matter mean diffusivity are present and suggest early axonal damage. Such changes are not accompanied by significant gray matter volume loss and are consistent with proposed models of pathological progression of the disease. Structural MRI, especially diffusion tensor imaging analysis, offers potential as a noninvasive biomarker reflecting cognitive impairment in PD.

Duncan GW ，Firbank MJ ，Yarnall AJ ，Khoo TK ，Brooks DJ ，Barker RA ，Burn DJ ，O'Brien JT ... -  《-》

A Multimodal Structural and Functional Neuroimaging Study of Amnestic Mild Cognitive Impairment.

Examination of brain structural and functional abnormalities in amnestic mild cognitive impairment (aMCI) has the potential to enhance our understanding of the initial pathophysiological changes in dementia. We examined gray matter volumes and white matter microstructural integrity, as well as resting state functional connectivity (rsFC) in patients with aMCI (N = 48) in comparison to elderly cognitively healthy comparison subjects (N = 48). Brain volumetric comparisons were carried out using voxel-based morphometric analysis of T1-weighted images using the FMRIB Software Library. White matter microstructural integrity was examined using whole-brain tract-based spatial statistics analysis of fractional anisotropy maps generated from diffusion tensor imaging data. Finally, rsFC differences between the samples were examined by Multivariate Exploratory Linear Optimised Decomposition into Independent Components of the resting state functional magnetic resonance imaging time series, followed by between-group comparisons of selected networks using dual regression analysis. Patients with aMCI showed significant gray matter volumetric reductions in bilateral parahippocampal gyri as well as multiple other brain regions including frontal, temporal, and parietal cortices. Additionally, reduced rsFC in the anterior subdivision of the default mode network (DMN) and increased rsFC in the executive network were noted in the absence of demonstrable impairment of white matter microstructural integrity. We conclude that the demonstrable neuroimaging findings in aMCI include significant gray matter volumetric reductions in the fronto-temporo-parietal structures as well as resting state functional connectivity disturbances in DMN and executive network. These findings differentiate aMCI from healthy aging and could constitute the earliest demonstrable neuroimaging findings of incipient dementia.

Bharath S ，Joshi H ，John JP ，Balachandar R ，Sadanand S ，Saini J ，Kumar KJ ，Varghese M ... -  《-》