Conventional functional magnetic resonance imaging using blood oxygenation level dependent contrast requires signal averaging and statistical methods to detect activation. Signal averaging implicitly ...assumes that brain activation in response to a stimulus is reproducible on the scale of the imaging voxel. This assumption is examined in the absence of averaging by analyzing individual trials of individual voxels that approach the size of the functional unit, the cortical column, in the human primary visual cortex. In the absence of spatial and temporal averaging, even highly active voxels demonstrate inconsistent activation to the same repeated stimulus despite consistent behavioral responses. This observation implies a variable selection of suitable cortical columns from a population of available functional units to produce consistent perception of the stimulus. The implication of this observation for neuroplasticity and behavioral consistency at the level of functional units is discussed.
Purpose
Ultrahigh field (UHF) resting state functional magnetic resonance imaging (rsfMRI) has become increasingly available for clinical and basic research, bringing improvements in resolution and ...contrast over standard high field imaging. Despite these improvements, UHF connectivity studies present several challenges, including increased sensitivity to physiological confounds and a vastly increased data burden. We present a direct quantitative assessment of test–retest reliability of functional connectivity in several standard functional networks between subjects scanned at 3T and 7T.
Methods
Five healthy subjects were scanned over four sessions each in a scan‐rescan design at both 3T and 7T field strengths. Resting state fMRI data were segmented into four major intrinsic connectivity networks, and seed‐based peak correlations within and between these networks examined. The reliability of these correlations was assessed using intra‐class correlation coefficients (ICC).
Results
Across all data, over 4000 peak correlations were extracted for assessment. The reliability over all intrinsic networks was greater at 7T than 3T (median ICC 0.40 vs. 0.33, p ≤ 0.0014), with each network individually showing improvement. Inter‐network reliability was stronger than intra‐network reliability, but intra‐network reliability showed the greatest improvement between field strengths.
Conclusion
We demonstrate significantly increased reliability of resting state connectivity at UHF strengths over conventional field strengths using a novel hybrid seed‐based analysis. This result adds to the growing body of work supporting the migration of functional imaging studies to UHFs.
The data burden for resting-state fMRI analysis rises with increasing resolutions available at ultrahigh fields. Therefore, a fundamental preprocessing step in brain network analysis is to reduce the ...data, usually by performing some kind of data parcellation. Most functional parcellations based on rsfMRI connectivity are synthesized from the dense connectome. In contrast, most network analyses begin by reducing each parcel to a single exemplar time series. This disconnect between parcel formation and usage assumes that parcel exemplars adequately represent their member voxels, which is not always the case for commonly used parcellations.
We propose to parcellate the brain based on parcel cohesion, a measure of similarity between a parcel’s exemplar and its member voxels. A spatially constrained agglomerative hierarchical framework is used to synthesize parcels based on a minimum cohesion threshold, rather than a predetermined number of parcels.
Cohesive parcellation generally results in more parcels than existing approaches. The number of parcels scales with the amount of smoothing in preprocessing, yet retains adequate information to extract common intrinsic functional networks.
Cohesive parcellation performs better than several widely used anatomical, functional, and data-driven parcellations on the basis of parcel cohesion and comparably using several traditional measures of cluster validity.
Cohesive parcellation ensures that the way parcels are synthesized directly corresponds to the way they are used in subsequent analyses. The resulting parcels are straightforward to interpret and optimal for downstream analysis.
•Parcel cohesion is defined as the functional similarity between a parcel’s exemplar and its members.•A novel parcellation based on optimizing parcel cohesion is presented.•Cohesive parcellation ensures that parcel formation matches parcel usage in downstream analyses.•Cohesive parcellation compares favorably to several widely used parcellations.
Methods for the analysis of event-related blood oxygenation level dependent (BOLD) fMRI data typically assume that the signal of interest consists of a fixed, reproducible hemodynamic response to ...repeated stimuli in the presence of a constant noise background. This assumption is not appropriate if the underlying functional units contributing to this signal activate stochastically, especially if the spatial resolution is such that only a small number of functional units are present in each voxel. A method for analyzing trial by trial consistency of high resolution voxels, called specified resolution wavelet analysis (SRWA), was developed to assess this deterministic assumption. Monte Carlo methods were used to evaluate the sensitivity and specificity of this technique with both synthetic and real data. Despite the typically low contrast to noise ratio of BOLD fMRI data, SRWA was sufficient for the identification of voxelwise activation on the individual trial level. Data were analyzed from the primary visual cortex (V1) of healthy human sujects performing a simple visual checkerboard task. The consistency of voxelwise activation from trial to trial was significantly less than assumed by a deterministic model at high spatial resolutions. The stochastic nature of this observed brain activity was not explained by fluctuations in behavior, physiology, movement, or any other of a number of common confounds typically found in fMRI experiments. Additionally, test insensitivity did not account for these low consistency rates. As spatial resolution is decreased, the observed activation became consistent with maps produced by traditional deterministic analyses, such as the t-test. Hence, the stochastic model of brain activity is compatible with traditional assumptions in the limit of spatiotemporal averaging. The decreasing activation consistency at increasing resolution suggests a stochastic selection of functional units from stimulus to stimulus. Although the brain responds to each event, the pattern of activation is not predetermined. Instead, identical stimuli can be processed by different collections of relevant functional units.
We report measurements of the dynamics of force relaxation in single mitotic chromosomes, following step strains applied with micropipettes of force constant approximately 1 nN/microm. The force ...relaxes exponentially after an elongation (l/l(0)) to less than 3x native length, with a relaxation time approximately 2 sec. This relaxation time corresponds to an effective viscosity approximately 10(5) times that of water. We experimentally rule out solvent flow into the chromosome as the mechanism for the relaxation time. Instead, the relaxation can be explained in terms of the disentanglement dynamics of approximately 80 kb chromatin loop domains.
We have quantitatively studied the space–time dynamics of mitotic chromosome compaction in cultured amphibian cells. After collecting digital phase-contrast images we have done digital image analysis ...to study spatial correlations in density. We find a characteristic distance at which the strongest correlations occur, which provides a quantitative measure of the size of patches of dense chromatin during interphase and early prophase. Later in mitosis, this length corresponds to the thickness of prophase and metaphase chromosomes. We find that during interphase strong correlations exist at a few-micrometer length; during prophase this correlation length progressively drops as the chromosomes are compacted. Our data are explained by a model based on assembly of chromatin loops onto already fiberlike interphase chromosomes. To test this model we have microinjected cobalt hexamine trichloride into interphase nuclei and have observed the rapid condensation of the interphase chromatin into thick fibers with a spacing similar to the native-state interphase correlation length determined from our image analysis.
Mitochondrial Ca2+ uniporter (MCU)-mediated Ca2+ uptake promotes the buildup of reducing equivalents that fuel oxidative phosphorylation for cellular metabolism. Although MCU modulates mitochondrial ...bioenergetics, its function in energy homeostasis in vivo remains elusive. Here we demonstrate that deletion of the Mcu gene in mouse liver (MCUΔhep) and in Danio rerio by CRISPR/Cas9 inhibits mitochondrial Ca2+ (mCa2+) uptake, delays cytosolic Ca2+ (cCa2+) clearance, reduces oxidative phosphorylation, and leads to increased lipid accumulation. Elevated hepatic lipids in MCUΔhep were a direct result of extramitochondrial Ca2+-dependent protein phosphatase-4 (PP4) activity, which dephosphorylates AMPK. Loss of AMPK recapitulates hepatic lipid accumulation without changes in MCU-mediated Ca2+ uptake. Furthermore, reconstitution of active AMPK, or PP4 knockdown, enhances lipid clearance in MCUΔhep hepatocytes. Conversely, gain-of-function MCU promotes rapid mCa2+ uptake, decreases PP4 levels, and reduces hepatic lipid accumulation. Thus, our work uncovers an MCU/PP4/AMPK molecular cascade that links Ca2+ dynamics to hepatic lipid metabolism.
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•Mitochondrial Ca2+ powers FAO-dependent hepatocyte mitochondrial respiration•Hepatic MCU deletion promotes lipid accumulation and lowers ketone bodies•Blockade of mCa2+ buffering enhances AMPK dephosphorylation through PP4•Restoration of AMPK activity in MCUΔhep model improves lipid clearance
Hepatic mitochondrial Ca2+ shapes bioenergetics and lipid homeostasis. Tomar et al. demonstrate that MCU-mediated cCa2+ buffering serves as a crucial step in controlling hepatic fuel metabolism through an MCU/PP4/AMPK molecular cascade. Identification of these molecular signaling events aids in understanding how perturbation of mitochondrial ion homeostasis may contribute to the etiology of metabolic disorders.
Ca2+ dynamics and oxidative signaling are fundamental mechanisms for mitochondrial bioenergetics and cell function. The MCU complex is the major pathway by which these signals are integrated ...in mitochondria. Whether and how these coactive elements interact with MCU have not been established. As an approach toward understanding the regulation of MCU channel by oxidative milieu, we adapted inflammatory and hypoxia models. We identified the conserved cysteine 97 (Cys-97) to be the only reactive thiol in human MCU that undergoes S-glutathionylation. Furthermore, biochemical, structural, and superresolution imaging analysis revealed that MCU oxidation promotes MCU higher order oligomer formation. Both oxidation and mutation of MCU Cys-97 exhibited persistent MCU channel activity with higher Ca2+m uptake rate, elevated mROS, and enhanced Ca2+m overload-induced cell death. In contrast, these effects were largely independent of MCU interaction with its regulators. These findings reveal a distinct functional role for Cys-97 in ROS sensing and regulation of MCU activity.
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•Mitochondrial Ca2+ uniporter complex core component senses mitochondrial ROS•MCU Cys-97 undergoes S-glutathionylation and exhibits as a higher-order oligomer•Interaction between MCU and its regulatory components is unaltered by MCU oxidation•Inflammatory/hypoxia signals promote MCU oxidation and sensitize cells to death
Dong et al. show that conserved MCU Cys-97 senses mitochondrial luminal ROS, and MCU oxidation promotes MCU higher-order oligomer formation and exhibits persistent activation of the MCU channel, elevated mitochondrial ROS, and enhanced Ca2+m overload-induced cell death. These findings reveal a distinct functional role for Cys-97 in mROS sensing and regulation of MCU activity.
Selective and smooth dielectric-on-dielectric was achieved by water-free single-precursor chemical vapor deposition (CVD) processes with the help of aniline passivation. Aniline selective passivation ...was demonstrated on W surfaces in preference to SiO2 at 250, 300, and 330 °C. After aniline passivation, selective HfO2, Al2O3, and TiO2 were deposited only on the HF-cleaned SiO2 surface by water-free single-precursor CVD using hafnium tert-butoxide Hf(O t Bu)4, aluminum-tri-sec-butoxide (ATSB), and titanium isopropoxide Ti(O i Pr)4 as the precursor reactants, respectively. Hf(O t Bu)4 and Ti(O i Pr)4 single-precursor CVD was carried out at 300 °C, while the ATSB CVD process was conducted at 330 °C. HfO2 and Al2O3 nanoselectivity tests were performed on W/SiO2 patterned samples. Transmission electron microscopy images of the W/SiO2 patterned samples after deposition demonstrated nanoselectivity and low surface roughness of HfO2 and Al2O3 deposition on the SiO2 regions only.
Selective and smooth dielectric-on-dielectric was achieved by water-free single-precursor chemical vapor deposition (CVD) processes with the help of aniline passivation. Aniline selective passivation ...was demonstrated on W surfaces in preference to SiO
at 250, 300, and 330 °C. After aniline passivation, selective HfO
, Al
O
, and TiO
were deposited only on the HF-cleaned SiO
surface by water-free single-precursor CVD using hafnium
-butoxide Hf(O
Bu)
, aluminum-tri-
-butoxide (ATSB), and titanium isopropoxide Ti(O
Pr)
as the precursor reactants, respectively. Hf(O
Bu)
and Ti(O
Pr)
single-precursor CVD was carried out at 300 °C, while the ATSB CVD process was conducted at 330 °C. HfO
and Al
O
nanoselectivity tests were performed on W/SiO
patterned samples. Transmission electron microscopy images of the W/SiO
patterned samples after deposition demonstrated nanoselectivity and low surface roughness of HfO
and Al
O
deposition on the SiO
regions only.
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