Resting-state functional magnetic resonance imaging (rfMRI) allows one to study functional connectivity in the brain by acquiring fMRI data while subjects lie inactive in the MRI scanner, and taking ...advantage of the fact that functionally related brain regions spontaneously co-activate. rfMRI is one of the two primary data modalities being acquired for the Human Connectome Project (the other being diffusion MRI). A key objective is to generate a detailed in vivo mapping of functional connectivity in a large cohort of healthy adults (over 1000 subjects), and to make these datasets freely available for use by the neuroimaging community. In each subject we acquire a total of 1h of whole-brain rfMRI data at 3T, with a spatial resolution of 2×2×2mm and a temporal resolution of 0.7s, capitalizing on recent developments in slice-accelerated echo-planar imaging. We will also scan a subset of the cohort at higher field strength and resolution. In this paper we outline the work behind, and rationale for, decisions taken regarding the rfMRI data acquisition protocol and pre-processing pipelines, and present some initial results showing data quality and example functional connectivity analyses.
•The Human Connectome Project is mapping brain connectivity in vivo in detail.•Resting-state fMRI (rfMRI) is a major modality in the Human Connectome Project.•We describe rfMRI acquisition and analysis protocols for the HCP.
Additive Combinatorics Tao, Terence; Vu, Van H.
09/2006, Letnik:
v.Series Number 105
eBook
Additive combinatorics is the theory of counting additive structures in sets. This theory has seen exciting developments and dramatic changes in direction in recent years thanks to its connections ...with areas such as number theory, ergodic theory and graph theory. This graduate-level 2006 text will allow students and researchers easy entry into this fascinating field. Here, the authors bring together in a self-contained and systematic manner the many different tools and ideas that are used in the modern theory, presenting them in an accessible, coherent, and intuitively clear manner, and providing immediate applications to problems in additive combinatorics. The power of these tools is well demonstrated in the presentation of recent advances such as Szemerédi's theorem on arithmetic progressions, the Kakeya conjecture and Erdos distance problems, and the developing field of sum-product estimates. The text is supplemented by a large number of exercises and new results.
Quantitative modeling of human brain activity can provide crucial insights about cortical representations 1, 2 and can form the basis for brain decoding devices 3–5. Recent functional magnetic ...resonance imaging (fMRI) studies have modeled brain activity elicited by static visual patterns and have reconstructed these patterns from brain activity 6–8. However, blood oxygen level-dependent (BOLD) signals measured via fMRI are very slow 9, so it has been difficult to model brain activity elicited by dynamic stimuli such as natural movies. Here we present a new motion-energy 10, 11 encoding model that largely overcomes this limitation. The model describes fast visual information and slow hemodynamics by separate components. We recorded BOLD signals in occipitotemporal visual cortex of human subjects who watched natural movies and fit the model separately to individual voxels. Visualization of the fit models reveals how early visual areas represent the information in movies. To demonstrate the power of our approach, we also constructed a Bayesian decoder 8 by combining estimated encoding models with a sampled natural movie prior. The decoder provides remarkable reconstructions of the viewed movies. These results demonstrate that dynamic brain activity measured under naturalistic conditions can be decoded using current fMRI technology.
► A new motion-energy model can describe BOLD signals evoked by natural movies ► The model reveals how motion information is represented in early visual areas ► Speed tuning in human early visual areas depends on eccentricity ► The model provides reconstructions of natural movies from evoked BOLD signals
Humans can see and name thousands of distinct object and action categories, so it is unlikely that each category is represented in a distinct brain area. A more efficient scheme would be to represent ...categories as locations in a continuous semantic space mapped smoothly across the cortical surface. To search for such a space, we used fMRI to measure human brain activity evoked by natural movies. We then used voxelwise models to examine the cortical representation of 1,705 object and action categories. The first few dimensions of the underlying semantic space were recovered from the fit models by principal components analysis. Projection of the recovered semantic space onto cortical flat maps shows that semantic selectivity is organized into smooth gradients that cover much of visual and nonvisual cortex. Furthermore, both the recovered semantic space and the cortical organization of the space are shared across different individuals.
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► The brain represents object and action categories within a continuous semantic space ► This semantic space is organized into broad gradients across the cortical surface ► This semantic space is shared across different individuals
Humans perceive thousands of object and action categories, so each category is likely not represented in a distinct brain area. Huth et al. use natural movie stimuli to show that categories are represented using a continuous semantic space that is shared across individuals and broadly mapped across the cortex.
Whole-brain functional magnetic resonance imaging (fMRI), in conjunction with multiband acceleration, has played an important role in mapping the functional connectivity throughout the entire brain ...with both high temporal and spatial resolution. Ultrahigh magnetic field strengths (7T and above) allow functional imaging with even higher functional contrast-to-noise ratios for improved spatial resolution and specificity compared to traditional field strengths (1.5T and 3T). High-resolution 7T fMRI, however, has primarily been constrained to smaller brain regions given the amount of time it takes to acquire the number of slices necessary for high resolution whole brain imaging. Here we evaluate a range of whole-brain high-resolution resting state fMRI protocols (0.9, 1.25, 1.5, 1.6 and 2mm isotropic voxels) at 7T, obtained with both in-plane and slice acceleration parallel imaging techniques to maintain the temporal resolution and brain coverage typically acquired at 3T. Using the processing pipeline developed by the Human Connectome Project, we demonstrate that high resolution images acquired at 7T provide increased functional contrast to noise ratios with significantly less partial volume effects and more distinct spatial features, potentially allowing for robust individual subject parcellations and descriptions of fine-scaled patterns, such as visuotopic organization.
About a quarter of human cerebral cortex is dedicated mainly to visual processing. The large-scale spatial organization of visual cortex can be measured with functional magnetic resonance imaging ...(fMRI) while subjects view spatially modulated visual stimuli, also known as "retinotopic mapping." One of the datasets collected by the Human Connectome Project involved ultrahigh-field (7 Tesla) fMRI retinotopic mapping in 181 healthy young adults (1.6-mm resolution), yielding the largest freely available collection of retinotopy data. Here, we describe the experimental paradigm and the results of model-based analysis of the fMRI data. These results provide estimates of population receptive field position and size. Our analyses include both results from individual subjects as well as results obtained by averaging fMRI time series across subjects at each cortical and subcortical location and then fitting models. Both the group-average and individual-subject results reveal robust signals across much of the brain, including occipital, temporal, parietal, and frontal cortex as well as subcortical areas. The group-average results agree well with previously published parcellations of visual areas. In addition, split-half analyses show strong within-subject reliability, further demonstrating the high quality of the data. We make publicly available the analysis results for individual subjects and the group average, as well as associated stimuli and analysis code. These resources provide an opportunity for studying fine-scale individual variability in cortical and subcortical organization and the properties of high-resolution fMRI. In addition, they provide a set of observations that can be compared with other Human Connectome Project measures acquired in these same participants.
The Human Connectome Project (HCP) relies primarily on three complementary magnetic resonance (MR) methods. These are: 1) resting state functional MR imaging (rfMRI) which uses correlations in the ...temporal fluctuations in an fMRI time series to deduce ‘functional connectivity’; 2) diffusion imaging (dMRI), which provides the input for tractography algorithms used for the reconstruction of the complex axonal fiber architecture; and 3) task based fMRI (tfMRI), which is employed to identify functional parcellation in the human brain in order to assist analyses of data obtained with the first two methods. We describe technical improvements and optimization of these methods as well as instrumental choices that impact speed of acquisition of fMRI and dMRI images at 3T, leading to whole brain coverage with 2mm isotropic resolution in 0.7s for fMRI, and 1.25mm isotropic resolution dMRI data for tractography analysis with three-fold reduction in total dMRI data acquisition time. Ongoing technical developments and optimization for acquisition of similar data at 7T magnetic field are also presented, targeting higher spatial resolution, enhanced specificity of functional imaging signals, mitigation of the inhomogeneous radio frequency (RF) fields, and reduced power deposition. Results demonstrate that overall, these approaches represent a significant advance in MR imaging of the human brain to investigate brain function and structure.
•We describe technical advances accomplished in the Human Connectome Project (HCP).•Highly accelerated imaging significantly improves fMRI and diffusion weighted MRI.•Instrumentation improvements in the HCP lead to superior diffusion-weighted MRI.•We describe of HCP efforts at both 3 and 7T, comparing their relative merits.•We describe recent developments with RF pulses for improved slice accelerated MRI.
The mainstream smoke yields of 14 polycyclic aromatic hydrocarbons (PAHs) were determined for 50 commercial U.S. cigarettes using a validated GC/MS method with the International Organization of ...Standardization (ISO) and Canadian Intense (CI) smoking machine regimens. PAH mainstream smoke deliveries vary widely among the commercial cigarettes with the ISO smoking regimen primarily because of differing filter ventilation. The more abundant, lower molecular weight PAHs such as naphthalene, fluorene, and phenanthrene predominantly comprise the total PAH yields. In contrast, delivery yields of high molecular weight PAHs such as benzobfluoranthene, benzoepyrene, benzokfluoranthene, and benzoapyrene (BaP) are much lower. Comparative analysis of PAHs deliveries shows brand specific differences. Correlation analysis shows strong positive associations between BaP and most of the other PAHs as well as total PAHs. The results suggest that BaP may be a representative marker for other PAH constituents in cigarette smoke generated from similarly blended tobacco, particularly those PAHs with similar molecular weights and chemical structures.
Encoding higher spatial resolution in simultaneous multi-slice (SMS) EPI is highly dependent on gradient performance, high density receiver coil arrays and pulse sequence optimization. We simulate ...gradient amplitude and slew rate determination of EPI imaging performance in terms of minimum TE, echo spacing (ES) and spatial resolution. We discuss the effects of image zooming in pulse sequences that have been used for sub-millimeter resolutions and the trade-offs in using partial Fourier and parallel imaging to reduce TE, PSF and ES. Using optimizations for SMS EPI pulse sequences with available gradient and receiver hardware, experimental results in ultra-high resolution (UHR) (0.45–0.5mm isotropic) SMS-EPI fMRI and mapping ocular dominance columns (ODC) in human brain at 0.5 mm isotropic resolution are demonstrated. We discuss promising future directions of UHR fMRI.
•To achieve unprecedented high-resolution fMRI of human brain at 7 Tesla:•We simulated the impact of magnetic gradient performance and image acquisition parameters (partial Fourier, parallel imaging, TE, echo spacing).•We demonstrated 0.45 − 0.5 mm isotropic fMRI with simultaneous multi-slice (SMS) EPI.•We demonstrated ocular dominance columns (ODCs) in 3D imaging through cortex depth.
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