2,367 research outputs found
How many ways a cell can move:the modes of self-propulsion of an active drop
Numerous physical models have been proposed to explain how cell motility
emerges from internal activity, mostly focused on how crawling motion arises
from internal processes. Here we offer a classification of self-propulsion
mechanisms based on general physical principles, showing that crawling is not
the only way for cells to move on a substrate. We consider a thin drop of
active matter on a planar substrate and fully characterize its autonomous
motion for all three possible sources of driving: (i) the stresses induced in
the bulk by active components, which allow in particular tractionless motion,
(ii) the self-propulsion of active components at the substrate, which gives
rise to crawling motion, and (iii) a net capillary force, possibly
self-generated, and coupled to internal activity. We determine travelling-wave
solutions to the lubrication equations as a function of a dimensionless
activity parameter for each mode of motion. Numerical simulations are used to
characterize the drop motion over a wide range of activity magnitudes, and
explicit analytical solutions in excellent agreement with the simulations are
derived in the weak-activity regime.Comment: to appear in Soft Matter (2020
An analysis of MRI derived cortical complexity in premature-born adults : regional patterns, risk factors, and potential significance
Premature birth bears an increased risk for aberrant brain development concerning its structure and function. Cortical complexity (CC) expresses the fractal dimension of the brain surface and changes during neurodevelopment. We hypothesized that CC is altered after premature birth and associated with long-term cognitive development.
One-hundred-and-one very premature-born adults (gestational age <32 weeks and/or birth weight <1500 âg) and 111 term-born adults were assessed by structural MRI and cognitive testing at 26 years of age. CC was measured based on MRI by vertex-wise estimation of fractal dimension. Cognitive performance was measured based on Griffiths-Mental-Development-Scale (at 20 months) and Wechsler-Adult-Intelligence-Scales (at 26 years).
In premature-born adults, CC was decreased bilaterally in large lateral temporal and medial parietal clusters. Decreased CC was associated with lower gestational age and birth weight. Furthermore, decreased CC in the medial parietal cortices was linked with reduced full-scale IQ of premature-born adults and mediated the association between cognitive development at 20 months and IQ in adulthood.
Results demonstrate that CC is reduced in very premature-born adults in temporoparietal cortices, mediating the impact of prematurity on impaired cognitive development. These data indicate functionally relevant long-term alterations in the brainâs basic geometry of cortical organization in prematurity
Sequelae of premature birth in young adults
Background and Purpose
Qualitative studies about the abnormalities appreciated on routine magnetic resonance imaging (MRI) sequences in prematurely born adults are lacking. This article aimed at filling this knowledge gap by (1) qualitatively describing routine imaging findings in prematurely born adults, (2) evaluating measures for routine image interpretation and (3) investigating the impact of perinatal variables related to premature birth.
Methods
In this study two board-certified radiologists assessed T1-weighted and FLAIR-weighted images of 100 prematurely born adults born very preterm (VP <32 weeks) and/or at very low birth weight (VLBW <1500âŻg) and 106 controls born at full term (FT) (mean age 26.8âŻÂąâ0.7 years). The number of white matter lesions (WML) was counted according to localization. Lateral ventricle volume (LVV) was evaluated subjectively and by measurements of Evansâ index (EI) and frontal-occipital-horn ratio (FOHR). Freesurfer-based volumetry served as reference standard. Miscellaneous incidental findings were noted as free text.
Results
The LVV was increased in 24.7% of VP/VLBW individuals and significantly larger than in FT controls. This was best identified by measurement of FOHR (AUCâŻ=â0.928). Ventricular enlargement was predicted by low gestational age (odds ratio: 0.71, 95% CI 0.51â0.98) and presence of neonatal intracranial hemorrhage (odds ratio: 0.26, 95% CI 0.07â0.92). The numbers of deep and periventricular WML were increased while subcortical WMLs were not.
Conclusion
Enlargement of the LVV and deep and periventricular WMLs are typical sequelae of premature birth that can be appreciated on routine brain MRI. To increase sensitivity of abnormal LVV detection, measurement of FOHR seems feasible in clinical practice
Insulator-to-metal transition in sulfur-doped silicon
We observe an insulator-to-metal (I-M) transition in crystalline silicon
doped with sulfur to non- equilibrium concentrations using ion implantation
followed by pulsed laser melting and rapid resolidification. This I-M
transition is due to a dopant known to produce only deep levels at equilibrium
concentrations. Temperature-dependent conductivity and Hall effect measurements
for temperatures T > 1.7 K both indicate that a transition from insulating to
metallic conduction occurs at a sulfur concentration between 1.8 and 4.3 x
10^20 cm-3. Conduction in insulating samples is consistent with variable range
hopping with a Coulomb gap. The capacity for deep states to effect metallic
conduction by delocalization is the only known route to bulk intermediate band
photovoltaics in silicon.Comment: Submission formatting; 4 journal pages equivalen
Minimally conscious state âplusâ: diagnostic criteria and relation to functional recovery
peer reviewedBackground: We investigated the relationship between three language-dependent behaviors (i.e., command-following, intelligible verbalization, and intentional communication) and the functional status of patients with disorders of consciousness (DoC). We hypothesized that patients in minimally conscious state (MCS) who retain behavioral evidence of preserved language function would have similar levels of functional disability, while patients who lack these behaviors would demonstrate significantly greater disability. We reasoned that these results could then be used to establish empirically-based diagnostic criteria for MCS+. Methods: In this retrospective cohort study we included rehabilitation inpatients diagnosed with DoC following severe-acquired brain injury (MCS = 57; vegetative state/unresponsive wakefulness syndrome [VS/UWS] = 63); women: 46; mean age: 47 Âą 19 years; traumatic etiology: 68; time post-injury: 40 Âą 23 days). We compared the scores of the Disability Rating Scale score (DRS) at time of transition from VS/UWS to MCS or from MCSâ to MCS+, and at discharge between groups. Results: Level of disability on the DRS was similar in patients with any combination of the three language-related behaviors. MCS patients with no behavioral evidence of language function (i.e., MCSâ) were more functionally impaired than patients with MCS+ at time of transition and at discharge. Conclusions: Command-following, intelligible verbalization, and intentional communication are not associated with different levels of functional disability. Thus, the MCS+ syndrome can be diagnosed based on the presence of any one of these language-related behaviors. Patients in MCS+ may evidence less functional disability compared to those in MCS who fail to demonstrate language function (i.e., MCSâ). Š 2019, Springer-Verlag GmbH Germany, part of Springer Nature
Impaired structural connectivity between dorsal attention network and pulvinar mediates the impact of premature birth on adult visualâspatial abilities
The dorsal attention network (DAN), including frontal eye fields and posterior parietal cortices, and its link with the posterior thalamus, contribute to visualâspatial abilities. Very premature birth impairs both visualâspatial abilities and corticoâthalamic structural connectivity. We hypothesized that impaired structural DANâpulvinar connectivity mediates the effect of very premature birth on adult visualâspatial abilities. Seventy very premature (median age 26.6âyears) and 57 mature born adults (median age 26.6âyears) were assessed with cognitive tests and diffusion tensor imaging. Perceptual organization (PO) index of the Wechsler Adult Intelligence ScaleâIII was used as a proxy for visualâspatial abilities, and connection probability maps in the thalamus, derived from probabilistic tractography from the DAN, were used as a proxy for DANâthalamic connectivity. Premature born adults showed decreases in both POâindex and connection probability from DAN into the pulvinar, with both changes being positively correlated. Moreover, path analysis revealed that DANâpulvinar connectivity mediates the relationship between very premature birth and POâindex. Results provide evidence for longâterm effects of very premature birth on structural DANâpulvinar connectivity, mediating the effect of prematurity on adult visualâspatial impairments. Data suggest DANâpulvinar connectivity as a specific target of prognostic and diagnostic procedures for visualâspatial abilities after premature birth
Does non-invasive brain stimulation modify hand dexterity? Protocol for a systematic review and meta-analysis
peer reviewedIntroduction: Dexterity is described as coordinated hand and finger movement for precision tasks. It is essential for day-to-day activities like computer use, writing or buttoning a shirt. Integrity of brain motor networks is crucial to properly execute these fine hand tasks. When these networks are damaged, interventions to enhance recovery are frequently accompanied by unwanted side effects or limited in their effect. Non-invasive brain stimulation (NIBS) are postulated to target affected motor areas and improve hand motor function with few side effects. However, the results across studies vary, and the current literature does not allow us to draw clear conclusions on the use of NIBS to promote hand function recovery. Therefore, we developed a protocol for a systematic review and meta-analysis on the effects of different NIBS technologies on dexterity in diverse populations. This study will potentially help future evidence-based research and guidelines that use these NIBS technologies for recovering hand dexterity. Methods and analysis: This protocol will compare the effects of active versus sham NIBS on precise hand activity. Records will be obtained by searching relevant databases. Included articles will be randomised clinical trials in adults, testing the therapeutic effects of NIBS on continuous dexterity data. Records will be studied for risk of bias. Narrative and quantitative synthesis will be done. Ethics and dissemination: No private health information is included; the study is not interventional. Ethical approval is not required. The results will be reported in a peer-review journal. Š 2017 Article author(s). All rights reserved
Aberrant gyrification contributes to the link between gestational age and adult IQ after premature birth
Gyrification is a hallmark of human brain development, starting in the second half of gestation in primary cortices, followed by unimodal and then transmodal associative cortices. Alterations in gyrification have been noted in premature-born newborns and children, suggesting abnormal cortical folding to be a permanent feature of prematurity. Furthermore, both gyrification and prematurity are tightly linked with cognitive performance, indicating a link between prematurity, gyrification, and cognitive performance. To investigate this triangular relation, we tested the following two hypotheses: (i) gyrification is aberrant in premature-born adults; and (ii) aberrant gyrification contributes to the impact of prematurity on adult cognitive performance. One hundred and one very premature-born adults (i.e. adults born before 32 weeks of gestation, and/or with birth weight <1500 g) and 111 mature-born adults were assessed by structural MRI and cognitive testing at 27 years of age. Gyrification was measured by local cortical absolute mean curvature (AMC), evaluated through structural MRI. Cognitive performance was assessed by the Wechsler Adult Intelligence Scale, full-scale IQ test. Two-sample t-tests, regression and mediation analyses were used to assess AMC group differences and the relation between AMC, birth-related variables, and full-scale IQ. Three key findings were identified. First, local AMC was widely increased in fronto-temporo-parietal primary and associative cortices of very premature-born adults. Increase of AMC was inversely associated with gestational age and birth weight and positively associated with medical complications at birth, respectively. Second, increased AMC of temporal associative cortices specifically contributed to the association between prematurity and reduced adult IQ (two-path mediation), indicating that aberrant gyrification of temporal associative cortices is critical for impaired cognitive performance after premature birth. Finally, further investigation of the relationship of gyrification between the early folding postcentral cortices and associative temporal cortices, folding later during neurodevelopment, revealed that the effect of gyrification abnormalities in associative temporal cortices on adult IQ is influenced itself by gyrification abnormalities occurring in the early folding postcentral cortices (three-path mediation). These results indicate that gyrification development across cortical areas in the brain conveys prematurity effects on adult IQ. Overall, these results provide evidence that premature birth leads to permanently aberrant gyrification patterns suggesting an altered neurodevelopmental trajectory. Statistical mediation modelling suggests that both aberrant gyrification itself as well as its propagation across the cortex express aspects of impaired neurodevelopment after premature birth and lead to reduced cognitive performance in adulthood. Thus, markers of gyrification appear as potential candidates for prognosis and treatment of prematurity effects
Reduced apparent fiber density in the white matter of premature-born adults
Premature-born adults exhibit lasting white matter alterations as demonstrated by widespread reduction in fractional anisotropy (FA) based on diffusion-weighted imaging (DWI). FA reduction, however, is non-specific for microscopic underpinnings such as aberrant myelination or fiber density (FD). Using recent advances in DWI, we tested the hypothesis of reduced FD in premature-born adults and investigated its link with the degree of prematurity and cognition. 73 premature- and 89 mature-born adults aged 25â27 years underwent single-shell DWI, from which a FD measure was derived using convex optimization modeling for microstructure informed tractography (COMMIT). Premature-born adults exhibited lower FD in numerous tracts including the corpus callosum and corona radiata compared to mature-born adults. These FD alterations were associated with both the degree of prematurity, as assessed via gestational age and birth weight, as well as with reduced cognition as measured by full-scale IQ. Finally, lower FD overlapped with lower FA, suggesting lower FD underlie unspecific FA reductions. Results provide evidence that premature birth leads to lower FD in adulthood which links with lower full-scale IQ. Data suggest that lower FD partly underpins FA reductions of premature birth but that other processes such as hypomyelination might also take place
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