scholarly journals Spatial specificity of the functional MRI blood oxygenation response relative to neuronal activity

2016 ◽  
Author(s):  
Denis Chaimow ◽  
Essa Yacoub ◽  
Kâmil Uğurbil ◽  
Amir Shmuel
Keyword(s):  
Functional Mri ◽  
Spatial Organization ◽  
Ocular Dominance ◽  
Blood Oxygenation ◽  
7 Tesla ◽  
Published Data ◽  
Model Parameters ◽  
Bold Fmri ◽  
Bold Imaging ◽  
Spatial Specificity

AbstractPrevious attempts at characterizing the spatial specificity of the blood oxygenation level dependent functional MRI (BOLD fMRI) response by estimating its point-spread function (PSF) have conventionally relied on spatial representations of visual stimuli in area V1. Consequently, their estimates were confounded by the width and scatter of receptive fields of V1 neurons. Here, we circumvent these limits by instead using the inherent cortical spatial organization of ocular dominance columns (ODCs) to determine the PSF for both Gradient Echo (GE) and Spin Echo (SE) BOLD imaging at 7 Tesla. By applying Markov Chain Monte Carlo sampling on a probabilistic generative model of imaging ODCs, we quantified the PSFs that best predict the spatial structure and magnitude of differential ODCs’ responses. Prior distributions for the ODC model parameters were determined by analyzing published data of cytochrome oxidase patterns from post-mortem histology of human V1 and of neurophysio-logical ocular dominance indices. The most probable PSF full-widths at halfmaximum were 0.82 mm (SE) and 1.02 mm (GE). Our results provide a quantitative basis for the spatial specificity of BOLD fMRI at ultra-high fields, which can be used for planning and interpretation of high-resolution differential fMRI of fine-scale cortical organizations.

scholarly journals Medullary vein architecture modulates the white matter BOLD cerebrovascular reactivity signal response to CO2: observations from high-resolution T2* weighted imaging at 7T

2021 ◽  
Author(s):  
Alex A. Bhogal
Keyword(s):  
White Matter ◽  
High Resolution ◽  
Vascular Reactivity ◽  
Blood Oxygenation ◽  
Cerebrovascular Reactivity ◽  
7 Tesla ◽  
Hemodynamic Parameters ◽  
Vascular Control ◽  
Bold Imaging ◽  
Anatomical Images

ABSTRACTBrain stress testing using blood oxygenation level-dependent (BOLD) MRI to evaluate changes in cerebrovascular reactivity (CVR) is of growing interest for evaluating white matter integrity. However, even under healthy conditions, the white matter BOLD-CVR response differs notably from that observed in the gray matter. In addition to actual arterial vascular control, the venous draining topology may influence the WM-CVR response leading to signal delays and dispersions. These types of alterations in hemodynamic parameters are sometimes linked with pathology, but may also arise from differences in normal venous architecture. In this work, high-resolution T2*weighted anatomical images combined with BOLD imaging during a hypercapnic breathing protocol were acquired using a 7 tesla MRI system. Hemodynamic parameters including base CVR, hemodynamic lag, lag-corrected CVR, response onset and signal dispersion, and finally ΔCVR (corrected CVR minus base CVR) were calculated in 8 subjects. Parameter maps were spatially normalized and correlated against an MNI-registered white matter medullary vein atlas. Moderate correlations (Pearson’s rho) were observed between medullary vessel frequency (MVF) and ΔCVR (0.52; 0.58 for total WM), MVF and hemodynamic lag (0.42; 0.54 for total WM), MVF and signal dispersion (0.44; 0.53 for total WM), and finally MVF and signal onset (0.43; 0.52 for total WM). Results indicate that, when assessed in the context of the WM venous architecture, changes in the response shape may only be partially reflective of the actual vascular reactivity response occurring further upstream by control vessels. This finding may have implications when attributing diseases mechanisms and/or progression to presumed impaired WM BOLD-CVR.

scholarly journals BRIDGING THE GAP BETWEEN NEUROIMAGING AND NEURONAL PHYSIOLOGY

2011 ◽  
Vol 21 (2) ◽  
pp. 97 ◽  
Author(s):  
Dae-Shik Kim ◽  
Kamil Ugurbil
Keyword(s):  
Functional Mri ◽  
Functional Neuroimaging ◽  
Explanatory Power ◽  
Blood Oxygenation ◽  
Functional Magnetic Resonance ◽  
Neural Correlate ◽  
Neuroimaging Data ◽  
Oxygenation Level ◽  
Spatial Specificity ◽  
Neuronal Physiology

Despite the fact that blood oxygenation level dependent (BOLD) functional magnetic resonance imaging (fMRI) studies have become ubiquitous and are of ever increasing importance for clinical and basic neurosciences, the fundamental relationships between BOLD and the underlying neuronal physiology are not understood. This raises severe concerns about the validity of BOLD contrast per se, and the conceptual frameworks currently employed in interpreting cognitive neuroimaging data. In order to expand the explanatory power of functional MRI data, several crucial questions will have to be addressed. The two most important questions are: First, what is the ultimate spatial resolution of fMRI?, secondly, what is the "neural correlate" of functional MRI? This article attempts to compile a series of results from our and other laboratories, suggesting that both the questions of "spatial specificity" and "neural correlate" might be within the reach of a tentative solution, thus finally bridging the gap between functional neuroimaging and neuronal physiology.

scholarly journals Neurochemical and BOLD Responses during Neuronal Activation Measured in the Human Visual Cortex at 7 Tesla

2015 ◽  
Vol 35 (4) ◽  
pp. 601-610 ◽  
Author(s):  
Petr Bednařík ◽  
Ivan Tkáč ◽  
Federico Giove ◽  
Mauro DiNuzzo ◽  
Dinesh K Deelchand ◽  
...  
Keyword(s):  
Magnetic Resonance ◽  
Visual Stimulation ◽  
Blood Oxygenation ◽  
7 Tesla ◽  
Single Subject ◽  
Resonance Spectroscopy ◽  
Functional Magnetic Resonance ◽  
Bold Fmri ◽  
Bold Responses ◽  
Concentration Changes

Several laboratories have consistently reported small concentration changes in lactate, glutamate, aspartate, and glucose in the human cortex during prolonged stimuli. However, whether such changes correlate with blood oxygenation level—dependent functional magnetic resonance imaging (BOLD-fMRI) signals have not been determined. The present study aimed at characterizing the relationship between metabolite concentrations and BOLD-fMRI signals during a block-designed paradigm of visual stimulation. Functional magnetic resonance spectroscopy (fMRS) and fMRI data were acquired from 12 volunteers. A short echo-time semi-LASER localization sequence optimized for 7 Tesla was used to achieve full signal-intensity MRS data. The group analysis confirmed that during stimulation lactate and glutamate increased by 0.26±0.06 μmol/g (∼30%) and 0.28±0.03 μmol/g (∼3%), respectively, while aspartate and glucose decreased by 0.20±0.04 μmol/g (∼5%) and 0.19±0.03 μmol/g (∼16%), respectively. The single-subject analysis revealed that BOLD-fMRI signals were positively correlated with glutamate and lactate concentration changes. The results show a linear relationship between metabolic and BOLD responses in the presence of strong excitatory sensory inputs, and support the notion that increased functional energy demands are sustained by oxidative metabolism. In addition, BOLD signals were inversely correlated with baseline γ-aminobutyric acid concentration. Finally, we discussed the critical importance of taking into account linewidth effects on metabolite quantification in fMRS paradigms.

scholarly journals Robust detection of ocular dominance columns in humans using Hahn Spin Echo BOLD functional MRI at 7 Tesla

NeuroImage ◽  
2007 ◽  
Vol 37 (4) ◽  
pp. 1161-1177 ◽  
Author(s):  
Essa Yacoub ◽  
Amir Shmuel ◽  
Nikos Logothetis ◽  
Kâmil Uğurbil
Keyword(s):  
Functional Mri ◽  
Spin Echo ◽  
Ocular Dominance ◽  
7 Tesla ◽  
Robust Detection ◽  
Ocular Dominance Columns

scholarly journals Inhibition of Voltage-Dependent Sodium Channels Suppresses the Functional Magnetic Resonance Imaging Response to Forepaw Somatosensory Activation in the Rodent

2001 ◽  
Vol 21 (5) ◽  
pp. 585-591 ◽  
Author(s):  
Ikuhiro Kida ◽  
Fahmeed Hyder ◽  
Kevin L. Behar
Keyword(s):  
Magnetic Resonance Imaging ◽  
Magnetic Resonance ◽  
Functional Magnetic Resonance Imaging ◽  
Blood Oxygenation ◽  
7 Tesla ◽  
Dependent Manner ◽  
Functional Magnetic Resonance ◽  
Resonance Imaging ◽  
Bold Fmri ◽  
Voltage Dependent

Results of recent studies suggest that the glutamate–glutamine neurotransmitter cycle between neurons and astrocytes plays a major role in the generation of the functional imaging signal. In the current study, the authors tested the hypothesis that activation of voltage-dependent Na+ channels is involved in the blood oxygenation level-dependent (BOLD) functional magnetic resonance imaging (fMRI) responses during somatosensory activation. The BOLD fMRI and cerebral blood flow (CBF) experiments were performed at 7 Tesla on α-chloralose–anesthetized rats undergoing forepaw stimulation before and for successive times after application of lamotrigine, a neuronal voltage-dependent Na+ channel blocker and glutamate release inhibitor. The BOLD fMRI signal changes in response to forepaw stimulation decreased in a time-dependent manner from 6.7% ± 0.7% before lamotrigine injection to 3.0% ± 2.5% between 60 and 105 minutes after lamotrigine treatment. After lamotrigine treatment, the fractional increase in CBF during forepaw stimulation was an order of magnitude less than that observed before the treatment. Lamotrigine had no effect on baseline CBF in the somatosensory cortex in the absence of stimulation. These results strongly suggest that activation of voltage-dependent Na+ channels is involved in the BOLD fMRI responses during somatosensory activation of the rat cortex.

scholarly journals Spatial specificity of the functional MRI blood oxygenation response relative to neuronal activity

NeuroImage ◽  
2018 ◽  
Vol 164 ◽  
pp. 32-47 ◽  
Author(s):  
Denis Chaimow ◽  
Essa Yacoub ◽  
Kâmil Uğurbil ◽  
Amir Shmuel
Keyword(s):  
Functional Mri ◽  
Neuronal Activity ◽  
Blood Oxygenation ◽  
Spatial Specificity

scholarly journals New Mathematical Modeling Approach for Predicting Microbial Inactivation by High Hydrostatic Pressure

2007 ◽  
Vol 73 (8) ◽  
pp. 2468-2478 ◽  
Author(s):  
Bernadette Klotz ◽  
D. Leo Pyle ◽  
Bernard M. Mackey
Keyword(s):  
Microbial Inactivation ◽  
Inactivation Kinetics ◽  
Published Data ◽  
Model Parameters ◽  
Order Kinetic ◽  
Square Root ◽  
Additional Time ◽  
Decimal Reduction Time ◽  
First Order ◽  
Primary Model

ABSTRACT A new primary model based on a thermodynamically consistent first-order kinetic approach was constructed to describe non-log-linear inactivation kinetics of pressure-treated bacteria. The model assumes a first-order process in which the specific inactivation rate changes inversely with the square root of time. The model gave reasonable fits to experimental data over six to seven orders of magnitude. It was also tested on 138 published data sets and provided good fits in about 70% of cases in which the shape of the curve followed the typical convex upward form. In the remainder of published examples, curves contained additional shoulder regions or extended tail regions. Curves with shoulders could be accommodated by including an additional time delay parameter and curves with tails shoulders could be accommodated by omitting points in the tail beyond the point at which survival levels remained more or less constant. The model parameters varied regularly with pressure, which may reflect a genuine mechanistic basis for the model. This property also allowed the calculation of (a) parameters analogous to the decimal reduction time D and z, the temperature increase needed to change the D value by a factor of 10, in thermal processing, and hence the processing conditions needed to attain a desired level of inactivation; and (b) the apparent thermodynamic volumes of activation associated with the lethal events. The hypothesis that inactivation rates changed as a function of the square root of time would be consistent with a diffusion-limited process.

scholarly journals Functional MRI during hyperbaric oxygen: Effects of oxygen on neurovascular coupling and BOLD fMRI signals

NeuroImage ◽  
2015 ◽  
Vol 119 ◽  
pp. 382-389 ◽  
Author(s):  
Damon P. Cardenas ◽  
Eric R. Muir ◽  
Shiliang Huang ◽  
Angela Boley ◽  
Daniel Lodge ◽  
...  
Keyword(s):  
Functional Mri ◽  
Hyperbaric Oxygen ◽  
Neurovascular Coupling ◽  
Bold Fmri ◽  
Oxygen Effects

Encoding of graded changes in spatial specificity of prior cues in human visual cortex

2014 ◽  
Vol 112 (11) ◽  
pp. 2834-2849 ◽  
Author(s):  
Yuko Hara ◽  
Justin L. Gardner
Keyword(s):  
Prior Information ◽  
Prior Probability ◽  
Blood Oxygenation ◽  
Response Magnitude ◽  
Behavioral Performance ◽  
Significant Difference ◽  
Cortical Responses ◽  
Sensory Responses ◽  
Contrast Discrimination ◽  
Spatial Specificity

Prior information about the relevance of spatial locations can vary in specificity; a single location, a subset of locations, or all locations may be of potential importance. Using a contrast-discrimination task with four possible targets, we asked whether performance benefits are graded with the spatial specificity of a prior cue and whether we could quantitatively account for behavioral performance with cortical activity changes measured by blood oxygenation level-dependent (BOLD) imaging. Thus we changed the prior probability that each location contained the target from 100 to 50 to 25% by cueing in advance 1, 2, or 4 of the possible locations. We found that behavioral performance (discrimination thresholds) improved in a graded fashion with spatial specificity. However, concurrently measured cortical responses from retinotopically defined visual areas were not strictly graded; response magnitude decreased when all 4 locations were cued (25% prior probability) relative to the 100 and 50% prior probability conditions, but no significant difference in response magnitude was found between the 100 and 50% prior probability conditions for either cued or uncued locations. Also, although cueing locations increased responses relative to noncueing, this cue sensitivity was not graded with prior probability. Furthermore, contrast sensitivity of cortical responses, which could improve contrast discrimination performance, was not graded. Instead, an efficient-selection model showed that even if sensory responses do not strictly scale with prior probability, selection of sensory responses by weighting larger responses more can result in graded behavioral performance benefits with increasing spatial specificity of prior information.

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