Divergent functional connectivity changes associated with white matter hyperintensities.

Age-related white matter hyperintensities are a common feature and are known to be negatively associated with structural integrity, functional connectivity, and cognitive performance. However, this has yet to be fully understood mechanistically. We analyzed multiple MRI modalities acquired in 465 non-demented individuals from the Swedish BioFINDER study including 334 cognitively normal and 131 participants with mild cognitive impairment. White matter hyperintensities were automatically quantified using fluid-attenuated inversion recovery MRI and parameters from diffusion tensor imaging were estimated in major white matter fibre tracts. We calculated fMRI resting state-derived functional connectivity within and between predefined cortical regions structurally linked by the white matter tracts. How change in functional connectivity is affected by white matter lesions and related to cognition (in the form of executive function and processing speed) was explored. We examined the functional changes using a measure of sample entropy. As expected hyperintensities were associated with disrupted structural white matter integrity and were linked to reduced functional interregional lobar connectivity, which was related to decreased processing speed and executive function. Simultaneously, hyperintensities were also associated with increased intraregional functional connectivity, but only within the frontal lobe. This phenomenon was also associated with reduced cognitive performance. The increased connectivity was linked to increased entropy (reduced predictability and increased complexity) of the involved voxels' blood oxygenation level-dependent signal. Our findings expand our previous understanding of the impact of white matter hyperintensities on cognition by indicating novel mechanisms that may be important beyond this particular type of brain lesions.

Association Between Earliest Amyloid Uptake and Functional Connectivity in Cognitively Unimpaired Elderly.

Alterations in cognitive performance have been noted in nondemented subjects with elevated accumulation of amyloid-ß (Aß) fibrils. However, it is not yet understood whether brain function is already influenced by Aß deposition during the very earliest stages of the disease. We therefore investigated associations between [18F]Flutemetamol PET, resting-state functional connectivity, gray and white matter structure and cognitive performance in 133 cognitively normal elderly that exhibited normal global Aß PET levels. [18F]Flutemetamol uptake in regions known to accumulate Aß fibrils early in preclinical AD (i.e., mainly certain parts of the default-mode network) was positively associated with dynamic but not static functional connectivity (r = 0.77). Dynamic functional connectivity was further related to better cognitive performance (r = 0.21-0.72). No significant associations were found for Aß uptake with gray matter volume or white matter diffusivity. The findings demonstrate that the earliest accumulation of Aß fibrils is associated with increased functional connectivity, which occurs before any structural alterations. The enhanced functional connectivity may reflect a compensatory mechanism to maintain high cognitive performance in the presence of increasing amyloid accumulation during the earliest phases of AD.

Functional connectivity changes in core resting state networks are associated with cognitive performance in systemic lupus erythematosus.

To investigate core resting state networks in SLE patients with and without neuropsychiatric symptoms by examining functional connectivity changes correlating with results of cognitive testing. Structural MRI and resting state-fMRI (rs-fMRI) were performed in 61 female SLE patients (mean age: 36.8 years, range 18.2-52.0 years) and 20 healthy controls (HC) (mean age 36.2 years, range 23.3-52.2 years) in conjunction with clinical examination and cognitive testing. Alterations in core resting state networks, not found in our healthy controls sample, correlated with cognitive performance gauged by neuropsychological tests in non-neuropsychiatric SLE (nNP) as well as in neuropsychiatric SLE patients (NP). The observed pattern of increased functional connectivity in core resting state networks correlated with reduced cognitive performance on all cognitive domains tested and with a heavy focus on DM, CE, and DM-CE in the NP subgroup. Furthermore, we found that the observed alterations in memory and psychomotor speed correlated with disease duration. In SLE patients both with and without clinically overt neuropsychiatric manifestations, we found changes in the functional connectivity of core resting state networks essential to cognitive functions. These findings may represent a rewiring of functional architecture in response to neuronal damage and could indicate suboptimal compensatory mechanisms at play.

Functional Connectivity Changes in Systemic Lupus Erythematosus: A Resting-State Study.

To investigate resting-state functional connectivity of lupus patients and associated subgroups according to the ACR NPSLE case definitions (ACR ad hoc). In addition, we investigated whether or not the observed alterations correlated with disease duration, the systemic lupus erythematosus (SLE)-Disease Activity Index-2000 (SLEDAI-2k), and Systemic Lupus International Collaborating Clinical/ACR organ damage index (SDI)-scores. Anatomical 3T magnetic resonance imaging (MRI) and resting-state functional MRI were performed in 61 female lupus patients (mean age = 37.0 years, range = 18.2-52.0 years) and 20 gender- and age-matched controls (mean age = 36.2 years, range = 23.3-52.2 years) in conjunction with clinical examination and laboratory testing. Whole-brain voxelwise functional connectivity analysis with permutation testing was performed to extract network components that differed in lupus patients relative to healthy controls (HCs). Lupus patients exhibited both inter- and intranetwork hypo- and hyperconnectivity involving several crucial networks. We found reduced connectivity within the default mode network (DMN), the central executive network (CEN), and in-between the DMN and CEN in lupus patients. Increased connectivity was primarily observed within and between the sensory motor network in lupus patients when compared to HCs. Comparing lupus patients with and without neuropsychiatric symptoms, hypoconnectivity was more pronounced in the group with neuropsychiatric complaints. The functional connectivity of SLE patients was both positively and negatively correlated to duration of disease. We conclude that SLE patients in general and neuropsychiatric SLE patients in particular experience altered brain connectivity. These patterns may be due both to direct neuronal damage and compensatory mechanisms through neuronal rewiring and recruitment and may partly explain neuropsychiatric symptoms in SLE patients.

Transition-metal dimers and physical limits on magnetic anisotropy.

Recent advances in nanoscience have raised interest in the minimum bit size required for classical information storage. This bit size is determined by the necessity for bistability with suppressed quantum tunnelling and energy barriers that exceed ambient temperatures. In the case of magnetic information storage, much attention has centred on molecular magnets with bits consisting of about 100 atoms, magnetic uniaxial anisotropy energy barriers of about 50 K and very slow relaxation at low temperatures. Here, we draw attention to the remarkable magnetic properties of some transition-metal dimers, which have energy barriers approaching 500 K with only two atoms. The spin dynamics of these ultrasmall nanomagnets is strongly affected by a Berry phase, which arises from quasi-degeneracies at the electronic highest occupied molecular orbital energy. In a giant-spin approximation, this Berry phase makes the effective reversal barrier thicker.