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Comparison of anterior cingulate vs. insular cortex as targets for real-time fMRI regulation during pain stimulation

Emmert, Kirsten; Breimhorst, Markus; Bauermann, Thomas; Birklein, Frank; Van De Ville, Dimitri; Haller, Sven
Fonte: Frontiers Media S.A. Publicador: Frontiers Media S.A.
Tipo: Artigo de Revista Científica
Publicado em 09/10/2014 Português
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26.79%
Real-time functional magnetic resonance imaging (rt-fMRI) neurofeedback allows learning voluntary control over specific brain areas by means of operant conditioning and has been shown to decrease pain perception. To further increase the effect of rt-fMRI neurofeedback on pain, we directly compared two different target regions of the pain network, notably the anterior insular cortex (AIC) and the anterior cingulate cortex (ACC). Participants for this prospective study were randomly assigned to two age-matched groups of 14 participants each (7 females per group) for AIC and ACC feedback. First, a functional localizer using block-design heat pain stimulation was performed to define the pain-sensitive target region within the AIC or ACC. Second, subjects were asked to down-regulate the BOLD activation in four neurofeedback runs during identical pain stimulation. Data analysis included task-related and functional connectivity analysis. At the behavioral level, pain ratings significantly decreased during feedback vs. localizer runs, but there was no difference between AIC and ACC groups. Concerning neuroimaging, ACC and AIC showed consistent involvement of the caudate nucleus for subjects that learned down-regulation (17/28) in both task-related and functional connectivity analysis. The functional connectivity toward the caudate nucleus is stronger for the ACC while the AIC is more heavily connected to the ventrolateral prefrontal cortex. Consequently...

EEG-fMRI Evaluation of Patients with Mesial Temporal Lobe Sclerosis

Avesani, Mirko; Giacopuzzi, Silvia; Bongiovanni, Luigi Giuseppe; Borelli, Paolo; Cerini, Roberto; Pozzi Mucelli, Roberto; Fiaschi, Antonio
Fonte: Centauro S.r.l. Publicador: Centauro S.r.l.
Tipo: Artigo de Revista Científica
Português
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This preliminary study sought more information on blood oxygen level dependent (BOLD) activation, especially contralateral temporal/extratemporal spread, during continuous EEG-fMRI recordings in four patients with mesial temporal sclerosis (MTS). In two patients, EEG showed unilateral focal activity during the EEG-fMRI session concordant with the interictal focus previously identified with standard and video-poly EEG. In the other two patients EEG demonstrated a contralateral diffusion of the irritative focus. In the third patient (with the most drug-resistant form and also extratemporal clinical signs), there was an extratemporal diffusion over frontal regions, ipsilateral to the irritative focus. fMRI analysis confirmed a single activation in the mesial temporal region in two patients whose EEG showed unilateral focal activity, while it demonstrated a bilateral activation in the mesial temporal regions in the other two patients. In the third patient, fMRI demonstrated an activation in the supplementary motxor area. This study confirms the most significant activation with a high firing rate of the irritative focus, but also suggests the importance of using new techniques (such as EEG-fMRI to examine cerebral blood flow) to identify the controlateral limbic activation...

Biophysical Modeling of Phase Changes in BOLD fMRI

Feng, Zhaomei; Caprihan, Arvind; Blagoev, Krastan B.; Calhoun, Vince D
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Português
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In BOLD fMRI, stimulus related phase changes have been repeatedly observed in humans. However, virtually all fMRI processing utilizes the magnitude information only, while ignoring the phase. This results in an unnecessary loss of physiological information and signal-to-noise efficiency. A widely held view is that the BOLD phase change is zero for a voxel containing randomly orientated blood vessels and that phase changes are only due to the presence of large vessels. Based on a previously developed theoretical model, we show through simulations and experimental human BOLD fMRI data that a non-zero phase change can be present in a region with randomly oriented vessels. Using simulations of the model, we first demonstrate that a spatially distributed susceptibility results in a non-zero phase distribution. Next, experimental data in a finger-tapping experiment show consistent bipolar phase distribution across multiple subjects. This model is then used to show that in theory a bipolar phase distribution can also be produced by the model. Finally, we show that the model can produce a bipolar phase pattern consistent with that observed in the experimental data. Understanding of the mechanisms behind the experimentally observed phase changes in BOLD fMRI would be an important step forward and will enable biophysical model based methods for integrating the phase and magnitude information in BOLD fMRI experiments.

The physics of functional magnetic resonance imaging (fMRI)

Buxton, Richard B
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Português
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Functional magnetic resonance imaging (fMRI) is a methodology for detecting dynamic patterns of activity in the working human brain. Although the initial discoveries that led to fMRI are only about 20 years old, this new field has revolutionized the study of brain function. The ability to detect changes in brain activity has a biophysical basis in the magnetic properties of deoxyhemoglobin, and a physiological basis in the way blood flow increases more than oxygen metabolism when local neural activity increases. These effects translate to a subtle increase in the local magnetic resonance signal, the blood oxygenation level dependent (BOLD) effect, when neural activity increases. With current techniques, this pattern of activation can be measured with resolution approaching 1 mm3 spatially and 1 s temporally. This review focuses on the physical basis of the BOLD effect, the imaging methods used to measure it, the possible origins of the physiological effects that produce a mismatch of blood flow and oxygen metabolism during neural activation, and the mathematical models that have been developed to understand the measured signals. An overarching theme is the growing field of quantitative fMRI, in which other MRI methods are combined with BOLD methods and analyzed within a theoretical modeling framework to derive quantitative estimates of oxygen metabolism and other physiological variables. That goal is the current challenge for fMRI: to move fMRI from a mapping tool to a quantitative probe of brain physiology.

Response of the medial temporal lobe network in amnestic mild cognitive impairment to therapeutic intervention assessed by fMRI and memory task performance

Bakker, Arnold; Albert, Marilyn S.; Krauss, Gregory; Speck, Caroline L.; Gallagher, Michela
Fonte: Elsevier Publicador: Elsevier
Tipo: Artigo de Revista Científica
Publicado em 21/02/2015 Português
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Studies of individuals with amnestic mild cognitive impairment (aMCI) have detected hyperactivity in the hippocampus during task-related functional magnetic resonance imaging (fMRI). Such elevated activation has been localized to the hippocampal dentate gyrus/CA3 (DG/CA3) during performance of a task designed to detect the computational contributions of those hippocampal circuits to episodic memory. The current investigation was conducted to test the hypothesis that greater hippocampal activation in aMCI represents a dysfunctional shift in the normal computational balance of the DG/CA3 regions, augmenting CA3-driven pattern completion at the expense of pattern separation mediated by the dentate gyrus. We tested this hypothesis using an intervention based on animal research demonstrating a beneficial effect on cognition by reducing excess hippocampal neural activity with low doses of the atypical anti-epileptic levetiracetam. In a within-subject design we assessed the effects of levetiracetam in three cohorts of aMCI participants, each receiving a different dose of levetiracetam. Elevated activation in the DG/CA3 region, together with impaired task performance, was detected in each aMCI cohort relative to an aged control group. We observed significant improvement in memory task performance under drug treatment relative to placebo in the aMCI cohorts at the 62.5 and 125 mg BID doses of levetiracetam. Drug treatment in those cohorts increased accuracy dependent on pattern separation processes and reduced errors attributable to an over-riding effect of pattern completion while normalizing fMRI activation in the DG/CA3 and entorhinal cortex. Similar to findings in animal studies...

Is Model Fitting Necessary for Model-Based fMRI?

Wilson, Robert C.; Niv, Yael
Fonte: Public Library of Science Publicador: Public Library of Science
Tipo: Artigo de Revista Científica
Publicado em 18/06/2015 Português
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26.79%
Model-based analysis of fMRI data is an important tool for investigating the computational role of different brain regions. With this method, theoretical models of behavior can be leveraged to find the brain structures underlying variables from specific algorithms, such as prediction errors in reinforcement learning. One potential weakness with this approach is that models often have free parameters and thus the results of the analysis may depend on how these free parameters are set. In this work we asked whether this hypothetical weakness is a problem in practice. We first developed general closed-form expressions for the relationship between results of fMRI analyses using different regressors, e.g., one corresponding to the true process underlying the measured data and one a model-derived approximation of the true generative regressor. Then, as a specific test case, we examined the sensitivity of model-based fMRI to the learning rate parameter in reinforcement learning, both in theory and in two previously-published datasets. We found that even gross errors in the learning rate lead to only minute changes in the neural results. Our findings thus suggest that precise model fitting is not always necessary for model-based fMRI. They also highlight the difficulty in using fMRI data for arbitrating between different models or model parameters. While these specific results pertain only to the effect of learning rate in simple reinforcement learning models...

Contrasting brain patterns of writing-related DTI parameters, fMRI connectivity, and DTI–fMRI connectivity correlations in children with and without dysgraphia or dyslexia

Richards, T.L.; Grabowski, T.J.; Boord, P.; Yagle, K.; Askren, M.; Mestre, Z.; Robinson, P.; Welker, O.; Gulliford, D.; Nagy, W.; Berninger, V.
Fonte: Elsevier Publicador: Elsevier
Tipo: Artigo de Revista Científica
Publicado em 28/03/2015 Português
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Based on comprehensive testing and educational history, children in grades 4–9 (on average 12 years) were diagnosed with dysgraphia (persisting handwriting impairment) or dyslexia (persisting word spelling/reading impairment) or as typical writers and readers (controls). The dysgraphia group (n = 14) and dyslexia group (n = 17) were each compared to the control group (n = 9) and to each other in separate analyses. Four brain region seed points (left occipital temporal gyrus, supramarginal gyrus, precuneus, and inferior frontal gyrus) were used in these analyses which were shown in a metaanalysis to be related to written word production on four indicators of white matter integrity and fMRI functional connectivity for four tasks (self-guided mind wandering during resting state, writing letter that follows a visually displayed letter in alphabet, writing missing letter to create a correctly spelled real word, and planning for composing after scanning on topic specified by researcher). For those DTI indicators on which the dysgraphic group or dyslexic group differed from the control group (fractional anisotropy, relative anisotropy, axial diffusivity but not radial diffusivity), correlations were computed between the DTI parameter and fMRI functional connectivity for the two writing tasks (alphabet and spelling) by seed points. Analyses...

Integration of multimodal neuroimaging methods: a rationale for clinical applications of simultaneous EEG-fMRI

Vitali, Paolo; Di Perri, Carol; Vaudano, Anna Elisabetta; Meletti, Stefano; Villani, Flavio
Fonte: CIC Edizioni Internationali Publicador: CIC Edizioni Internationali
Tipo: Artigo de Revista Científica
Publicado em 27/07/2015 Português
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Functional magnetic resonance imaging (fMRI), which has high spatial resolution, is increasingly used to evaluate cerebral functions in neurological and psychiatric diseases. The main limitation of fMRI is that it detects neural activity indirectly, through the associated slow hemodynamic variations. Because neurovascular coupling can be regionally altered by pathological conditions or drugs, fMRI responses may not truly reflect neural activity. Electroencephalography (EEG) recordings, which directly detect neural activity with optimal temporal resolution, can now be obtained during fMRI data acquisition. Therefore, there is a growing interest in combining the techniques to obtain simultaneous EEG-fMRI recordings.

Predictors of Therapy Effects: Studies on Procedural Learning in Healthy Elderly and Stroke Patients; Einflussfaktoren auf Therapieeffekte – Lernstudien an Gesunden und Schlaganfallpatienten

Lam, Judith My Lin
Fonte: Universidade de Tubinga Publicador: Universidade de Tubinga
Tipo: Dissertação
Português
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26.79%
In recent years the focus of stroke rehabilitation research has changed from approaches which only compensate patient disability to approaches which seek to understand the underlying mechanisms, in particular how to stimulate the recovery of the brain (Nadeau,2002; Dobkin,2004). Knowledge about plasticity of the brain, learning mechanisms, and search for predictors of functional outcome after injury and therapy drive the recent rehabilitation research in a promising direction. Existent rehabilitation programs such as treadmill aerobic exercise training have shown group effects, but the variability of benefit within the group is quite large. Finding predictors of therapy-related benefits in treadmill training will help to adjust the program to individual stroke patients. To this end, in the first study we pooled data from two randomized controlled trials of treadmill aerobic exercise training and included clinical, demographic, and lesion-related factors as possible predictors (independent variables) of baseline performance and change of performance in fitness and walking parameters (dependent variables). We showed that patients with smaller and left-sided lesions benefit the most from treadmill training and that shorter stroke-therapy interval has a positive effect on improvement. However...

Versiones dispersas de máquinas de vectores soporte para la reconstrucción de mapas de activación en fMRI

Cristobal Huerta, Alexandra
Fonte: Universidade Carlos III de Madrid Publicador: Universidade Carlos III de Madrid
Tipo: info:eu-repo/semantics/bachelorThesis; info:eu-repo/semantics/masterThesis Formato: application/pdf
Português
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La técnica de Imágenes de Resonancia Magnética (MRI) está cobrando especial importancia en el campo de la medicina y de la investigación, ya que es una técnica muy útil para el diagnóstico médico porque permite detectar una variedad de afecciones, desde rupturas de ligamentos hasta tumores. La técnica de Imágenes de Resonancia Magnética Funcional (fMRI) permite analizar la actividad cerebral y detectar las áreas cerebrales relacionadas con una determinada tarea. Para ello, empleando una secuencia de imágenes de Resonancia magnética obtenidas mientras que el paciente está realizando una determinada tarea jada, se pueden emplear métodos estadísticos capaces de obtener un mapa de activación cerebral que indique que zona del cerebro se encarga o está relacionada con la tarea en cuestión. Actualmente, para la reconstrucción de estos mapas, la técnica más empleada es el mapeo estadístico paramétrico (SPM), el cual es un software que haciendo uso de técnicas de regresión lineal, permite la reconstrucción de los mapas de activación. El problema de esta técnica es que utiliza métodos univariantes, no teniéndose en cuenta así las relaciones existentes entre las diferentes áreas e, incluso, entre los diferentes voxels que componen el mapa de activación. Al ignorarse esta propiedad...

Similarity of fMRI activity patterns in left perirhinal cortex reflects semantic similarity between words

Bruffaerts, R.; Dupont, P.; Peeters, R.; De Deyne, S.; Storms, G.; Vandenberghe, R.
Fonte: Society for Neuroscience Publicador: Society for Neuroscience
Tipo: Artigo de Revista Científica
Publicado em //2013 Português
Relevância na Pesquisa
26.79%
How verbal and nonverbal visuoperceptual input connects to semantic knowledge is a core question in visual and cognitive neuroscience, with significant clinical ramifications. In an event-related functional magnetic resonance imaging (fMRI) experiment we determined how cosine similarity between fMRI response patterns to concrete words and pictures reflects semantic clustering and semantic distances between the represented entities within a single category. Semantic clustering and semantic distances between 24 animate entities were derived from a concept-feature matrix based on feature generation by >1000 subjects. In the main fMRI study, 19 human subjects performed a property verification task with written words and pictures and a low-level control task. The univariate contrast between the semantic and the control task yielded extensive bilateral occipitotemporal activation from posterior cingulate to anteromedial temporal cortex. Entities belonging to a same semantic cluster elicited more similar fMRI activity patterns in left occipitotemporal cortex. When words and pictures were analyzed separately, the effect reached significance only for words. The semantic similarity effect for words was localized to left perirhinal cortex. According to a representational similarity analysis of left perirhinal responses...

Solutions to various problems in reversible cooling fMRI studies; Solutions to various problems in reversible cooling functional magnetic resonance imaging studies

Khachaturian, Mark Haig, 1979-
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 51 p.; 1155448 bytes; 2427367 bytes; application/pdf; application/pdf
Português
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Functional magnetic resonance imaging (fMRI) has been very useful in helping neuroscientists map the brain. One tool to investigate the interactions between brain regions is to disable a small region in the brain, and look at the functional consequences of this (reversible) inactivation upon regions anatomically connected to the inactivated site. A number of issues need to be resolved before the reversible cooling technique can be used in fMRI studies. The solutions to a number of problems directly related to using reversible inactivation by cooling in conjunction with fMRI experiments on monkey brains are presented in this thesis. Specifically, these include (1) designing a cooling system and cooling probe capable of reversibly cooling the surface cortex of the monkey's brain, (2) develop or use an existing method to measure the temperature distribution with the MR-scanner, and (3) design and construct a coil (phase array) that will be used to obtain temperature and fMRI data at the highest resolution possible. A cooling system and coolant probe were designed capable of changing the temperature of the surface cortex from 37 oC to 20 oC. The Proton Resonance Frequency Shift method, which calculates the temperature based on the phase change between two images...

Characterizing Response to Elemental Unit of Acoustic Imaging Noise: An fMRI Study

Tamer, Gregory G.; Luh, Wen-Ming; Talavage, Thomas M.
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Português
Relevância na Pesquisa
26.79%
Acoustic imaging noise produced during functional magnetic resonance imaging (fMRI) studies can hinder auditory fMRI research analysis by altering the properties of the acquired time-series data. Acoustic imaging noise can be especially confounding when estimating the time course of the hemodynamic response (HDR) in auditory event-related fMRI (fMRI) experiments. This study is motivated by the desire to establish a baseline function that can serve not only as a comparison to other quantities of acoustic imaging noise for determining how detrimental is one's experimental noise, but also as a foundation for a model that compensates for the response to acoustic imaging noise. Therefore, the amplitude and spatial extent of the HDR to the elemental unit of acoustic imaging noise (i.e., a single ping) associated with echoplanar acquisition were characterized and modeled. Results from this fMRI study at 1.5 T indicate that the group-averaged HDR in left and right auditory cortex to acoustic imaging noise (duration of 46 ms) has an estimated peak magnitude of 0.29% (right) to 0.48% (left) signal change from baseline, peaks between 3 and 5 s after stimulus presentation, and returns to baseline and remains within the noise range approximately 8 s after stimulus presentation.

Real-time fMRI Biofeedback Targeting the Orbitofrontal Cortex for Contamination Anxiety

Hampson, Michelle; Stoica, Teodora; Saksa, John; Scheinost, Dustin; Qiu, Maolin; Bhawnani, Jitendra; Pittenger, Christopher; Papademetris, Xenophon; Constable, Todd
Fonte: MyJove Corporation Publicador: MyJove Corporation
Tipo: Artigo de Revista Científica
Publicado em 20/01/2012 Português
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We present a method for training subjects to control activity in a region of their orbitofrontal cortex associated with contamination anxiety using biofeedback of real-time functional magnetic resonance imaging (rt-fMRI) data. Increased activity of this region is seen in relationship with contamination anxiety both in control subjects1 and in individuals with obsessive-compulsive disorder (OCD),2 a relatively common and often debilitating psychiatric disorder involving contamination anxiety. Although many brain regions have been implicated in OCD, abnormality in the orbitofrontal cortex (OFC) is one of the most consistent findings.3, 4 Furthermore, hyperactivity in the OFC has been found to correlate with OCD symptom severity5 and decreases in hyperactivity in this region have been reported to correlate with decreased symptom severity.6 Therefore, the ability to control this brain area may translate into clinical improvements in obsessive-compulsive symptoms including contamination anxiety. Biofeedback of rt-fMRI data is a new technique in which the temporal pattern of activity in a specific region (or associated with a specific distributed pattern of brain activity) in a subject's brain is provided as a feedback signal to the subject. Recent reports indicate that people are able to develop control over the activity of specific brain areas when provided with rt-fMRI biofeedback.7-12 In particular...

Phase-amplitude coupling and infraslow (<1 Hz) frequencies in the rat brain: relationship to resting state fMRI

Thompson, Garth J.; Pan, Wen-Ju; Billings, Jacob C. W.; Grooms, Joshua K.; Shakil, Sadia; Jaeger, Dieter; Keilholz, Shella D.
Fonte: Frontiers Media S.A. Publicador: Frontiers Media S.A.
Tipo: Artigo de Revista Científica
Publicado em 27/05/2014 Português
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26.79%
Resting state functional magnetic resonance imaging (fMRI) can identify network alterations that occur in complex psychiatric diseases and behaviors, but its interpretation is difficult because the neural basis of the infraslow BOLD fluctuations is poorly understood. Previous results link dynamic activity during the resting state to both infraslow frequencies in local field potentials (LFP) (<1 Hz) and band-limited power in higher frequency LFP (>1 Hz). To investigate the relationship between these frequencies, LFPs were recorded from rats under two anesthetics: isoflurane and dexmedetomidine. Signal phases were calculated from low-frequency LFP and compared to signal amplitudes from high-frequency LFP to determine if modulation existed between the two frequency bands (phase-amplitude coupling). Isoflurane showed significant, consistent phase-amplitude coupling at nearly all pairs of frequencies, likely due to the burst-suppression pattern of activity that it induces. However, no consistent phase-amplitude coupling was observed in rats that were anesthetized with dexmedetomidine. fMRI-LFP correlations under isoflurane using high frequency LFP were reduced when the low frequency LFP's influence was accounted for, but not vice-versa...

ADHD-200 Global Competition: diagnosing ADHD using personal characteristic data can outperform resting state fMRI measurements

Brown, Matthew R. G.; Sidhu, Gagan S.; Greiner, Russell; Asgarian, Nasimeh; Bastani, Meysam; Silverstone, Peter H.; Greenshaw, Andrew J.; Dursun, Serdar M.
Fonte: Frontiers Media S.A. Publicador: Frontiers Media S.A.
Tipo: Artigo de Revista Científica
Publicado em 28/09/2012 Português
Relevância na Pesquisa
26.79%
Neuroimaging-based diagnostics could potentially assist clinicians to make more accurate diagnoses resulting in faster, more effective treatment. We participated in the 2011 ADHD-200 Global Competition which involved analyzing a large dataset of 973 participants including Attention deficit hyperactivity disorder (ADHD) patients and healthy controls. Each participant's data included a resting state functional magnetic resonance imaging (fMRI) scan as well as personal characteristic and diagnostic data. The goal was to learn a machine learning classifier that used a participant's resting state fMRI scan to diagnose (classify) that individual into one of three categories: healthy control, ADHD combined (ADHD-C) type, or ADHD inattentive (ADHD-I) type. We used participants' personal characteristic data (site of data collection, age, gender, handedness, performance IQ, verbal IQ, and full scale IQ), without any fMRI data, as input to a logistic classifier to generate diagnostic predictions. Surprisingly, this approach achieved the highest diagnostic accuracy (62.52%) as well as the highest score (124 of 195) of any of the 21 teams participating in the competition. These results demonstrate the importance of accounting for differences in age...

CORRECTING INHOMOGENEITY-INDUCED DISTORTION IN FMRI USING NON-RIGID REGISTRATION

Chambers, Micah C.; Bhushan, Chitresh; Haldar, Justin P.; Leahy, Richard M.; Shattuck, David W.
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em /04/2015 Português
Relevância na Pesquisa
26.79%
Magnetic field inhomogeneities in echo planar images (EPI) can cause large distortion in the phase encoding dimension. In functional MRI (fMRI), this distortion can shift activation loci, increase inter subject variability, and reduce statistical power during group analysis. Distortion correction methods that make use of acquired magnetic field maps have been developed, however, field maps are not always acquired or may not be available to researchers. An alternative approach, which we pursue in this paper, is to estimate the distortion retrospectively by spatially registering the EPI to a structural MRI. We describe a constrained non-linear registration method for correcting fMRI distortion that uses T1-weighted images and does not require field maps. We compared resting state results from uncorrected fMRI, fMRI data corrected with field maps, and fMRI data corrected with our proposed method in data from 20 subjects. The results show that the estimated field maps were similar to the acquired field maps and that the proposed method reduces the overall error in independent component location.

Towards Robust and Specific Causal Discovery from fMRI

Zhang, Kun; Huang, Biwei; Schoelkopf, Bernhard; Besserve, Michel; Watanabe, Masataka; Zhu, Dajiang
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 27/09/2015 Português
Relevância na Pesquisa
26.79%
There are several issues with causal discovery from fMRI. First, the sampling frequency is so low that the time-delayed dependence between different regions is very small, making time-delayed causal relations weak and unreliable. Moreover, the complex correspondence between neural activity and the BOLD signal makes it difficult to formulate a causal model to represent the effect as a function of the cause. Second, the fMRI experiment may last a relatively long time period, during which the causal influences are likely to change along with certain unmeasured states (e.g., the attention) of the subject which can be written as a function of time, and ignoring the time-dependence will lead to spurious connections. Likewise, the causal influences may also vary as a function of the experimental condition (e.g., health, disease, and behavior). In this paper we aim to develop a principled framework for robust and time- or condition-specific causal discovery, by addressing the above issues. Motivated by a simplified fMRI generating process, we show that the time-delayed conditional independence relationships at the proper causal frequency of neural activities are consistent with the instantaneous conditional independence relationships between brain regions in fMRI recordings. Then we propose an enhanced constraint-based method for robust discovery of the underlying causal skeletons...

A blind deconvolution approach to recover effective connectivity brain networks from resting state fMRI data

Wu, G.; Liao, W.; Stramaglia, S.; Ding, J.; Chen, H.; Marinazzo, D.
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 18/08/2012 Português
Relevância na Pesquisa
26.79%
A great improvement to the insight on brain function that we can get from fMRI data can come from effective connectivity analysis, in which the flow of information between even remote brain regions is inferred by the parameters of a predictive dynamical model. As opposed to biologically inspired models, some techniques as Granger causality (GC) are purely data-driven and rely on statistical prediction and temporal precedence. While powerful and widely applicable, this approach could suffer from two main limitations when applied to BOLD fMRI data: confounding effect of hemodynamic response function (HRF) and conditioning to a large number of variables in presence of short time series. For task-related fMRI, neural population dynamics can be captured by modeling signal dynamics with explicit exogenous inputs; for resting-state fMRI on the other hand, the absence of explicit inputs makes this task more difficult, unless relying on some specific prior physiological hypothesis. In order to overcome these issues and to allow a more general approach, here we present a simple and novel blind-deconvolution technique for BOLD-fMRI signal. Coming to the second limitation, a fully multivariate conditioning with short and noisy data leads to computational problems due to overfitting. Furthermore...

Automatic multi-resolution spatio-frequence mottle metric (sfmm) for evaluation of macrouniformity

Khullar, Siddharth
Fonte: Rochester Instituto de Tecnologia Publicador: Rochester Instituto de Tecnologia
Tipo: Tese de Doutorado
Português
Relevância na Pesquisa
26.79%
Researchers in the field of functional neuroimaging have faced a long standing problem in pre-processing low spatial resolution data without losing meaningful details within. Commonly, the brain function is recorded by a technique known as echo-planar imaging that represents the measure of blood flow (BOLD signal) through a particular location in the brain as an array of intensity values changing over time. This approach to record a movie of blood flow in the brain is known as fMRI. The neural activity is then studied from the temporal correlation patterns existing within the fMRI time series. However, the resulting images are noisy and contain low spatial detail, thus making it imperative to pre-process them appropriately to derive meaningful activation patterns. Two of the several standard preprocessing steps employed just before the analysis stage are denoising and normalization. Fundamentally, it is difficult to perfectly remove noise from an image without making assumptions about signal and noise distributions. A convenient and commonly used alternative is to smooth the image with a Gaussian filter, but this method suffers from various obvious drawbacks, primarily loss of spatial detail. A greater challenge arises when we attempt to derive average activation patterns from fMRI images acquired from a group of individuals. The brain of one individual differs from others in a structural sense as well as in a functional sense. Commonly...