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NeuroImage Oct 2023Spatial attention is often described as a mental spotlight that enhances information processing at the attended location. Using fMRI, we investigated background...
Spatial attention is often described as a mental spotlight that enhances information processing at the attended location. Using fMRI, we investigated background connectivity between the pulvinar and V1 in relation to focused versus diffused attention allocation, in weak and strong crowding contexts. Our findings revealed that focused attention led to enhanced correlations between the pulvinar and V1. Notably, this modulation was initiated by the pulvinar, and the strength of the modulation was dependent on the saliency of the target. These findings suggest that the pulvinar initiates information reweighting to V1, which underlies attentional selection in cluttered scenes.
Topics: Humans; Pulvinar; Cognition; Diffusion
PubMed: 37619793
DOI: 10.1016/j.neuroimage.2023.120341 -
Comparative Biochemistry and... Mar 2021The capillary bed constitutes the obligatory pathway for almost all oxygen (O) and substrate molecules as they pass from blood to individual cells. As the largest organ,... (Review)
Review
The capillary bed constitutes the obligatory pathway for almost all oxygen (O) and substrate molecules as they pass from blood to individual cells. As the largest organ, by mass, skeletal muscle contains a prodigious surface area of capillaries that have a critical role in metabolic homeostasis and must support energetic requirements that increase as much as 100-fold from rest to maximal exercise. In 1919 Krogh's 3 papers, published in the Journal of Physiology, brilliantly conflated measurements of muscle capillary function at rest and during contractions with Agner K. Erlang's mathematical model of O diffusion. These papers single-handedly changed the perception of capillaries from passive vessels serving at the mercy of their upstream arterioles into actively contracting vessels that were recruited during exercise to elevate blood-myocyte O flux. Although seminal features of Krogh's model have not withstood the test of time and subsequent technological developments, Krogh is credited with helping found the field of muscle microcirculation and appreciating the role of the capillary bed and muscle O diffusing capacity in facilitating blood-myocyte O flux. Today, thanks in large part to Krogh, it is recognized that comprehending the role of the microcirculation, as it supports perfusive and diffusive O conductances, is fundamental to understanding skeletal muscle plasticity with exercise training and resolving the mechanistic bases by which major pathologies including heart failure and diabetes cripple exercise tolerance and cerebrovascular dysfunction predicates impaired executive function.
Topics: Animals; Capillaries; Diffusion; Humans; Muscle Cells; Muscles; Oxygen
PubMed: 33242636
DOI: 10.1016/j.cbpa.2020.110852 -
Biomaterials Oct 2023Flourished in the past two decades, fluorescent probe technology provides researchers with accurate and efficient tools for in situ imaging of biomarkers in living cells... (Review)
Review
Flourished in the past two decades, fluorescent probe technology provides researchers with accurate and efficient tools for in situ imaging of biomarkers in living cells and tissues and may play a significant role in clinical diagnosis and treatment such as biomarker detection, fluorescence imaging-guided surgery, and photothermal/photodynamic therapy. In situ imaging of biomarkers depends on the spatial resolution of molecular probes. Nevertheless, the majority of currently available molecular fluorescent probes suffer from the drawback of diffusing from the target region. This leads to a rapid attenuation of the fluorescent signal over time and a reduction in spatial resolution. Consequently, the diffused fluorescent signal cannot accurately reflect the in situ information of the target. Self-immobilizing and self-precipitating molecular fluorescent probes can be used to overcome this problem. These probes ensure that the fluorescent signal remains at the location where the signal is generated for a long time. In this review, we introduce the development history of the two types of probes and classify them in detail according to different design strategies. In addition, we compare their advantages and disadvantages, summarize some representative studies conducted in recent years, and propose prospects for this field.
Topics: Fluorescent Dyes; Molecular Probes; Diagnostic Imaging; Diffusion; Photothermal Therapy
PubMed: 37643487
DOI: 10.1016/j.biomaterials.2023.122281 -
The Journal of Physical Chemistry... Dec 2020Diffusivity of a protein (a Brownian particle) is caused by random molecular collisions in the Stokes-Einstein picture. Alternatively, it can be viewed as driven by...
Diffusivity of a protein (a Brownian particle) is caused by random molecular collisions in the Stokes-Einstein picture. Alternatively, it can be viewed as driven by unbalanced stochastic forces acting from water on the protein. Molecular dynamics simulations of protein mutants carrying different charges are analyzed here in terms of the van der Waals (vdW) and electrostatic forces acting on the protein. They turn out to be remarkably strongly correlated and the total force is largely a compensation between vdW and electrostatic forces. Both vdW and electrostatic forces relax on the same time scale of 5-6 ns separated by 6 orders of magnitude from the relaxation time of the total force. Similar phenomenology applies to the dynamics and statistics of the fluctuating torque responsible for rotational diffusion. Standard linear theories of dielectric friction are grossly inapplicable to translational and rotational diffusion of proteins overestimating friction by many orders of magnitude.
Topics: Diffusion; Molecular Dynamics Simulation; Proteins; Static Electricity
PubMed: 33191741
DOI: 10.1021/acs.jpclett.0c03006 -
Journal of Biological Physics Sep 2023We present an analysis of an epidemic spreading process on an Apollonian network that can describe an epidemic spreading in a non-sedentary population. We studied the...
We present an analysis of an epidemic spreading process on an Apollonian network that can describe an epidemic spreading in a non-sedentary population. We studied the modified diffusive epidemic process using the Monte Carlo method by computational analysis. Our model may be helpful for modeling systems closer to reality consisting of two classes of individuals: susceptible (A) and infected (B). The individuals can diffuse in a network according to constant diffusion rates [Formula: see text] and [Formula: see text], for the classes A and B, respectively, and obeying three diffusive regimes, i.e., [Formula: see text], [Formula: see text], and [Formula: see text]. Into the same site i, the reaction occurs according to the dynamical rule based on Gillespie's algorithm. Finite-size scaling analysis has shown that our model exhibits continuous phase transition to an absorbing state with a set of critical exponents given by [Formula: see text], [Formula: see text], and [Formula: see text] familiar to every investigated regime. In summary, the continuous phase transition, characterized by this set of critical exponents, does not have the same exponents of the mean-field universality class in both regular lattices and complex networks.
Topics: Humans; Computer Simulation; Algorithms; Epidemics; Models, Biological; Diffusion
PubMed: 37118345
DOI: 10.1007/s10867-023-09634-2 -
Physical Review. E Dec 2022A class of one-dimensional, discrete-time random walk models with memory, termed "random walk with n memory channels" (RWnMC), is proposed. In these models the...
A class of one-dimensional, discrete-time random walk models with memory, termed "random walk with n memory channels" (RWnMC), is proposed. In these models the information of n (n∈Z) previous steps from the walker's entire history is needed to decide a future step. Exact calculation of the mean and variance of position of the RW2MC (n=2) has been done, which shows that it can lead to asymptotic diffusive and superdiffusive behavior in different parameter regimes. A connection between RWnMC and a Pólya-type urn model evolving by drawing n balls at a time has also been reported. This connection for the RW2MC is discussed in detail and suggests the applicability of RW2MC in many population dynamics models with multiple competing species.
Topics: Diffusion; Walking; Population Dynamics; Diffusion Magnetic Resonance Imaging
PubMed: 36671173
DOI: 10.1103/PhysRevE.106.L062105 -
Journal of Neuroscience Methods Jan 2021Diffusion Magnetic Resonance Imaging (dMRI) is one of the most important contemporary non-invasive modalities for probing tissue structure at the microscopic scale. The... (Review)
Review
Diffusion Magnetic Resonance Imaging (dMRI) is one of the most important contemporary non-invasive modalities for probing tissue structure at the microscopic scale. The majority of dMRI techniques employ standard single diffusion encoding (SDE) measurements, covering different sequence parameter ranges depending on the complexity of the method. Although many signal representations and biophysical models have been proposed for SDE data, they are intrinsically limited by a lack of specificity. Advanced dMRI methods have been proposed to provide additional microstructural information beyond what can be inferred from SDE. These enhanced contrasts can play important roles in characterizing biological tissues, for instance upon diseases (e.g. neurodegenerative, cancer, stroke), aging, learning, and development. In this review we focus on double diffusion encoding (DDE), which stands out among other advanced acquisitions for its versatility, ability to probe more specific diffusion correlations, and feasibility for preclinical and clinical applications. Various DDE methodologies have been employed to probe compartment sizes (Section 3), decouple the effects of microscopic diffusion anisotropy from orientation dispersion (Section 4), probe displacement correlations, study exchange, or suppress fast diffusing compartments (Section 6). DDE measurements can also be used to improve the robustness of biophysical models (Section 5) and study intra-cellular diffusion via magnetic resonance spectroscopy of metabolites (Section 7). This review discusses all these topics as well as important practical aspects related to the implementation and contrast in preclinical and clinical settings (Section 9) and aims to provide the readers a guide for deciding on the right DDE acquisition for their specific application.
Topics: Anisotropy; Brain; Diffusion; Diffusion Magnetic Resonance Imaging; Magnetic Resonance Imaging; Magnetic Resonance Spectroscopy
PubMed: 33144100
DOI: 10.1016/j.jneumeth.2020.108989 -
The European Respiratory Journal Jul 2022
Topics: Carbon Monoxide; Diffusion; Humans; Pulmonary Diffusing Capacity
PubMed: 35902101
DOI: 10.1183/13993003.00789-2022 -
Biomedical Physics & Engineering Express Aug 2023. EDBreast gel is an alternative Fricke gel dosimeter, read by Magnetic Resonance Imaging, in which sucrose is added to lower diffusion effects. This paper aims at...
. EDBreast gel is an alternative Fricke gel dosimeter, read by Magnetic Resonance Imaging, in which sucrose is added to lower diffusion effects. This paper aims at determining the dosimetric characteristics of this dosimeter.. The characterization has been performed in high energy photon beams. The dose-response of the gel has been evaluated as well as its detection limit, its fading effects, the reproducibility of its response and its stability over time. Its energy and dose-rate dependence has been investigated, and the overall dose uncertainty budget established. Once characterized, the dosimetry method has been applied to a simple reference irradiation case in a 6 MV photon beam, with the measurement of the lateral dose profile of a 2 × 2 cmfield. The results have been compared with microDiamond measurements.. In addition to its low diffusivity, the gel presents a high sensitivity, no dose-rate dependence consideringTPR20-10values ranging from 0.66 to 0.79 and an energy response comparable to ionization chambers. However, its non-linear dose-response induces a high uncertainty on the measured dose (8 % (k=1) at 20 Gy) and reproducibility issues. The profile measurements displayed discrepancies compared to the microDiamond due to diffusion effects. The appropriate spatial resolution was estimated using the diffusion coefficient.. EDBreast gel dosimeter presents interesting characteristics for applications in clinics, but the linearity of its dose-response should be improved to lower the uncertainties and to enhance the reproducibility.
Topics: Reproducibility of Results; Radiometry; Diffusion; Radiation Dosimeters; Uncertainty
PubMed: 37236157
DOI: 10.1088/2057-1976/acd942 -
Magnetic Resonance in Medicine Dec 2021Microstructure imaging seeks to noninvasively measure and map microscopic tissue features by pairing mathematical modeling with tailored MRI protocols. This article... (Review)
Review
Microstructure imaging seeks to noninvasively measure and map microscopic tissue features by pairing mathematical modeling with tailored MRI protocols. This article reviews an emerging paradigm that has the potential to provide a more detailed assessment of tissue microstructure-combined diffusion-relaxometry imaging. Combined diffusion-relaxometry acquisitions vary multiple MR contrast encodings-such as b-value, gradient direction, inversion time, and echo time-in a multidimensional acquisition space. When paired with suitable analysis techniques, this enables quantification of correlations and coupling between multiple MR parameters-such as diffusivity, , , and . This opens the possibility of disentangling multiple tissue compartments (within voxels) that are indistinguishable with single-contrast scans, enabling a new generation of microstructural maps with improved biological sensitivity and specificity.
Topics: Brain; Diffusion; Diffusion Magnetic Resonance Imaging; Magnetic Resonance Imaging; Models, Theoretical
PubMed: 34411331
DOI: 10.1002/mrm.28963