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White matter microstructure underlying default mode network connectivity in the human brain

TEIPEL, Stefan J.; BOKDE, Arun L. W.; MEINDL, Thomas; AMARO JR., Edson; SOLDNER, Jasmin; REISER, Maximilian F.; HERPERTZ, Sabine C.; MOLLER, Hans-Jurgen; HAMPEL, Harald
Fonte: ACADEMIC PRESS INC ELSEVIER SCIENCE Publicador: ACADEMIC PRESS INC ELSEVIER SCIENCE
Tipo: Artigo de Revista Científica
Português
Relevância na Pesquisa
26.79%
Resting state functional magnetic resonance imaging (fMRI) reveals a distinct network of correlated brain function representing a default mode state of the human brain The underlying structural basis of this functional connectivity pattern is still widely unexplored We combined fractional anisotropy measures of fiber tract integrity derived from diffusion tensor imaging (DTI) and resting state fMRI data obtained at 3 Tesla from 20 healthy elderly subjects (56 to 83 years of age) to determine white matter microstructure e 7 underlying default mode connectivity We hypothesized that the functional connectivity between the posterior cingulate and hippocampus from resting state fMRI data Would be associated with the white matter microstructure in the cingulate bundle and fiber tracts connecting posterior cingulate gyrus With lateral temporal lobes, medial temporal lobes, and precuneus This was demonstrated at the p<0001 level using a voxel-based multivariate analysis of covariance (MANCOVA) approach In addition, we used a data-driven technique of joint independent component analysis (ICA) that uncovers spatial pattern that are linked across modalities. It revealed a pattern of white matter tracts including cingulate bundle and associated fiber tracts resembling the findings from the hypothesis-driven analysis and was linked to the pattern of default mode network (DMN) connectivity in the resting state fMRI data Out findings support the notion that the functional connectivity between the posterior cingulate and hippocampus and the functional connectivity across the entire DMN is based oil distinct pattern of anatomical connectivity within the cerebral white matter (C) 2009 Elsevier Inc All rights reserved; Medical Faculty Of the Ludwig-Maximilian University (Munich. Germany); Hirnliga e. V. (Nurmbrecht...

Effect of image analysis software on neurofunctional activation during processing of emotional human faces

FUSAR-POLI, P.; BHATTACHARYYA, S.; ALLEN, P.; CRIPPA, J. A.; BORGWARDT, S.; MARTIN-SANTOS, R.; SEAL, M.; O`CARROLL, C.; ATAKAN, Z.; ZUARDI, A. W.; MCGUIRE, P.
Fonte: ELSEVIER SCI LTD Publicador: ELSEVIER SCI LTD
Tipo: Artigo de Revista Científica
Português
Relevância na Pesquisa
26.79%
Functional brain imaging techniques such as functional MRI (fMRI) that allow the in vivo investigation of the human brain have been exponentially employed to address the neurophysiological substrates of emotional processing. Despite the growing number of fMRI studies in the field, when taken separately these individual imaging studies demonstrate contrasting findings and variable pictures, and are unable to definitively characterize the neural networks underlying each specific emotional condition. Different imaging packages, as well as the statistical approaches for image processing and analysis, probably have a detrimental role by increasing the heterogeneity of findings. In particular, it is unclear to what extent the observed neurofunctional response of the brain cortex during emotional processing depends on the fMRI package used in the analysis. In this pilot study, we performed a double analysis of an fMRI dataset using emotional faces. The Statistical Parametric Mapping (SPM) version 2.6 (Wellcome Department of Cognitive Neurology, London, UK) and the XBAM 3.4 (Brain Imaging Analysis Unit, Institute of Psychiatry, Kings College London, UK) programs, which use parametric and non-parametric analysis, respectively, were used to assess our results. Both packages revealed that processing of emotional faces was associated with an increased activation in the brain`s visual areas (occipital...

Detecção e caracterização da resposta hemodinâmica pelo desenvolvimento de novos métodos de processamento de imagens funcionais por ressonância magnética; Detection and estimation of the hemodynamic response by new functional magnetic resonance imaging methods

Sturzbecher, Marcio Junior
Fonte: Biblioteca Digitais de Teses e Dissertações da USP Publicador: Biblioteca Digitais de Teses e Dissertações da USP
Tipo: Dissertação de Mestrado Formato: application/pdf
Publicado em 20/04/2006 Português
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Os estímulos evento-relacionados (event-related functional magnetic resonance imaging - ER-fMRI) têm se tornado mais popular nos últimos anos. A maioria das análises das séries temporais geradas nesses exames é baseada em um modelo específico da função resposta hemodinâmica, hemodinamic response function (HRF). Contudo, a considerável variabilidade da HRF e a baixa relação sinal ruído das imagens, tem dificultado sua caracterização e localização. Neste sentido, recentemente foi proposto um método baseado na computação da entropia de Shannon, que não faz suposição sobre a forma da resposta. Desse modo, no presente trabalho, buscou-se, em um primeiro momento, avaliar alguns parâmetros do método proposto a fim de aumentar sua sensibilidade. Além disso, generalizou-se o método com a entropia de Tsallis, que introduz um novo parâmetro, q. Foi proposto, também, um novo método baseado no cálculo da distância de Kullback-Leibler (KL). Todos os métodos foram aplicados a dados simulados e dados reais. Curvas ROC (Receiver Operating Characteristic) foram usadas para estudar a dependência dos valores de corte e os diferentes parâmetros dos métodos em relação à sensibilidade e especificidade. A entropia de Tsallis apresentou maior poder de detecção nos intervalos de -1 < q < 1 (q diferente de 0) com dois níveis. O método de KL mostrou uma melhora significativa da sensibilidade em dados simulados e apresentou a habilidade em discriminar regiões funcionais ativas e em repouso...

Resting state fMRI experimental and analytical methodology: a functional connectivity analysis

Fernandes, Catarina Dinis
Fonte: Universidade de Lisboa Publicador: Universidade de Lisboa
Tipo: Dissertação de Mestrado
Publicado em //2013 Português
Relevância na Pesquisa
26.79%
Tese de mestrado integrado em Engenharia Biomédica e Biofísica , apresentada à Universidade de Lisboa, através da Faculdade de Ciências, 2013; O ser humano desde sempre se sentiu fascinado pelo estudo do seu próprio corpo assim como das suas propriedades funcionais. Do desejo de compreender e explorar o corpo humano surgiram então técnicas que permitem o seu estudo de modo não invasivo. Entre as primeiras técnicas de imagiologia encontram-se os Raios-X, a tomografia axial computadorizada (TAC) e a terapia por emissão de positrões (PET: do inglês “Positron Emission Therapy"). Contudo, todas elas utilizam radiação ionizante, e como tal surgiu o desejo de desenvolver novas metodologias igualmente não invasivas mas que por seu lado não utilizem qualquer tipo de radiação ionizante. Entre estas técnicas encontra-se a imagiologia por ressonância magnética (MRI: do inglês “Magnetic Resonance Imaging”) que pode ser utilizada para estudar as estruturas anatómicas mas também os seus mecanismos funcionais através da aplicação da técnica de ressonância magnética funcional (fMRI: do inglês “functional magnetic resonance imaging). Contrariamente às técnicas que utilizam radiação ionizante, a imagiologia por ressonância magnética tira partido do facto de o ser humano ser maioritariamente constituído por água. Um ser humano adulto é por norma constituído por cerca de 70 – 80% de água (H2O) o que se reflecte numa grande abundância de protões – núcleo 1H. Quando submetidos a um forte campo magnético...

Repeated BOLD-fMRI Imaging of Deep Brain Stimulation Responses in Rats

Chao, Tzu-Hao Harry; Chen, Jyh-Horng; Yen, Chen-Tung
Fonte: Public Library of Science Publicador: Public Library of Science
Tipo: Artigo de Revista Científica
Publicado em 13/05/2014 Português
Relevância na Pesquisa
26.84%
Functional magnetic resonance imaging (fMRI) provides a picture of the global spatial activation pattern of the brain. Interest is growing regarding the application of fMRI to rodent models to investigate adult brain plasticity. To date, most rodent studies used an electrical forepaw stimulation model to acquire fMRI data, with α-chloralose as the anesthetic. However, α-chloralose is harmful to animals, and not suitable for longitudinal studies. Moreover, peripheral stimulation models enable only a limited number of brain regions to be studied. Processing between peripheral regions and the brain is multisynaptic, and renders interpretation difficult and uncertain. In the present study, we combined the medetomidine-based fMRI protocol (a noninvasive rodent fMRI protocol) with chronic implantation of an MRI-compatible stimulation electrode in the ventroposterior (VP) thalamus to repetitively sample thalamocortical responses in the rat brain. Using this model, we scanned the forebrain responses evoked by the VP stimulation repeatedly of individual rats over 1 week. Cortical BOLD responses were compared between the 2 profiles obtained at day1 and day8. We discovered reproducible frequency- and amplitude-dependent BOLD responses in the ipsilateral somatosensory cortex (S1). The S1 BOLD responses during the 2 sessions were conserved in maximal response amplitude...

Multimodal Functional Imaging Using fMRI-Informed Regional EEG/MEG Source Estimation

Ou, Wanmei; Nummenmaa, Aapo; Hämäläinen, Matti; Golland, Polina
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em //2009 Português
Relevância na Pesquisa
26.84%
We propose a novel method, fMRI-Informed Regional Estimation (FIRE), which utilizes information from fMRI in E/MEG source reconstruction. FIRE takes advantage of the spatial alignment between the neural and the vascular activities, while allowing for substantial differences in their dynamics. Furthermore, with the regional approach, FIRE can be efficiently applied to a dense grid of sources. Inspection of our optimization procedure reveals that FIRE is related to the re-weighted minimum-norm algorithms, the difference being that the weights in the proposed approach are computed from both the current estimates and fMRI data. Analysis of both simulated and human fMRI-MEG data shows that FIRE reduces the ambiguities in source localization present in the minimum-norm estimates. Comparisons with several joint fMRI-E/MEG algorithms demonstrate robustness of FIRE in the presence of sources silent to either fMRI or E/MEG measurements.

Moving forward with fMRI data

Rugg, Michael D.; Thompson-Schill, Sharon L.
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em /01/2013 Português
Relevância na Pesquisa
26.84%
The use of fMRI to inform cognitive theory depends upon the assumption that there is an isomorphic relationship between functional states and brain states. Even if this assumption is accepted, employing fMRI to make cognitive inferences is not straightforward. We discuss these inferential difficulties, and describe an example where fMRI data has had a significant impact on a cognitive theory despite them. According to the embodied cognition framework, accessing a conceptual feature engages the same processes that are active when the feature is directly experienced. A consistent finding from fMRI studies is that accessing a feature activates cortical regions slightly anterior to the regions activated when the feature is experienced. We suggest that this neural dissociation between accessing and perceiving a feature is inconsistent with the strong form of embodied cognition theory, and that this inconsistency would likely not have been identified without fMRI. We describe how the observation of this forward-shift has led to new ways about thinking about perceptual and conceptual representations and the relation between them. Finally, we argue that despite the strong assumptions that are the needed to make functional inferences from fMRI...

Functional topography of the corpus callosum investigated by DTI and fMRI

Fabri, Mara; Pierpaoli, Chiara; Barbaresi, Paolo; Polonara, Gabriele
Fonte: Baishideng Publishing Group Inc Publicador: Baishideng Publishing Group Inc
Tipo: Artigo de Revista Científica
Português
Relevância na Pesquisa
26.84%
This short review examines the most recent functional studies of the topographic organization of the human corpus callosum, the main interhemispheric commissure. After a brief description of its anatomy, development, microstructure, and function, it examines and discusses the latest findings obtained using diffusion tensor imaging (DTI) and tractography (DTT) and functional magnetic resonance imaging (fMRI), three recently developed imaging techniques that have significantly expanded and refined our knowledge of the commissure. While DTI and DTT have been providing insights into its microstructure, integrity and level of myelination, fMRI has been the key technique in documenting the activation of white matter fibers, particularly in the corpus callosum. By combining DTT and fMRI it has been possible to describe the trajectory of the callosal fibers interconnecting the primary olfactory, gustatory, motor, somatic sensory, auditory and visual cortices at sites where the activation elicited by peripheral stimulation was detected by fMRI. These studies have demonstrated the presence of callosal fiber tracts that cross the commissure at the level of the genu, body, and splenium, at sites showing fMRI activation. Altogether such findings lend further support to the notion that the corpus callosum displays a functional topographic organization that can be explored with fMRI.

Two pitfalls of BOLD fMRI magnitude-based neuroimage analysis: non-negativity and edge effect

Chen, Zikuan; Calhoun, Vince D.
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Português
Relevância na Pesquisa
26.84%
BOLD fMRI is accepted as a noninvasive imaging modality for neuroimaging and brain mapping. A BOLD fMRI dataset consists of magnitude and phase components. Currently, only the magnitude is used for neuroimage analysis. In this paper, we show that the fMRI-magnitude-based neuroimage analysis may suffer two pitfalls: one is that the magnitude is non-negative and cannot differentiate positive from negative BOLD activity; the other is an edge effect that may manifest as an edge enhancement or a spatial interior dip artifact at a local uniform BOLD region. We demonstrate these pitfalls via numeric simulations using a BOLD fMRI model and also via a phantom experiment. We also propose a solution by making use of the fMRI phase image, the counterpart of the fMRI magnitude.

A Critical Role for Purinergic Signalling in the Mechanisms Underlying Generation of BOLD fMRI Responses

Wells, Jack A.; Christie, Isabel N.; Hosford, Patrick S.; Huckstepp, Robert T.R.; Angelova, Plamena R.; Vihko, Pirkko; Cork, Simon C.; Abramov, Andrey Y.; Teschemacher, Anja G.; Kasparov, Sergey; Lythgoe, Mark F.; Gourine, Alexander V.
Fonte: Society for Neuroscience Publicador: Society for Neuroscience
Tipo: Artigo de Revista Científica
Publicado em 01/04/2015 Português
Relevância na Pesquisa
26.84%
The mechanisms of neurovascular coupling underlying generation of BOLD fMRI signals remain incompletely understood. It has been proposed that release of vasoactive substances by astrocytes couples neuronal activity to changes in cerebrovascular blood flow. However, the role of astrocytes in fMRI responses remains controversial. Astrocytes communicate via release of ATP, and here we tested the hypothesis that purinergic signaling plays a role in the mechanisms underlying fMRI. An established fMRI paradigm was used to trigger BOLD responses in the forepaw region of the somatosensory cortex (SSFP) of an anesthetized rat. Forepaw stimulation induced release of ATP in the SSFP region. To interfere with purinergic signaling by promoting rapid breakdown of the vesicular and/or released ATP, a lentiviral vector was used to express a potent ectonucleotidase, transmembrane prostatic acid phosphatase (TMPAP), in the SSFP region. TMPAP expression had no effect on resting cerebral blood flow, cerebrovascular reactivity, and neuronal responses to sensory stimulation. However, TMPAP catalytic activity markedly reduced the magnitude of BOLD fMRI responses triggered in the SSFP region by forepaw stimulation. Facilitated ATP breakdown could result in accumulation of adenosine. However...

Optimizing Stimulation and Analysis Protocols for Neonatal fMRI

Cusack, Rhodri; Wild, Conor; Linke, Annika C.; Arichi, Tomoki; Lee, David S. C.; Han, Victor K.
Fonte: Public Library of Science Publicador: Public Library of Science
Tipo: Artigo de Revista Científica
Publicado em 12/08/2015 Português
Relevância na Pesquisa
26.84%
The development of brain function in young infants is poorly understood. The core challenge is that infants have a limited behavioral repertoire through which brain function can be expressed. Neuroimaging with fMRI has great potential as a way of characterizing typical development, and detecting abnormal development early. But, a number of methodological challenges must first be tackled to improve the robustness and sensitivity of neonatal fMRI. A critical one of these, addressed here, is that the hemodynamic response function (HRF) in pre-term and term neonates differs from that in adults, which has a number of implications for fMRI. We created a realistic model of noise in fMRI data, using resting-state fMRI data from infants and adults, and then conducted simulations to assess the effect of HRF of the power of different stimulation protocols and analysis assumptions (HRF modeling). We found that neonatal fMRI is most powerful if block-durations are kept at the lower range of those typically used in adults (full on/off cycle duration 25-30s). Furthermore, we show that it is important to use the age-appropriate HRF during analysis, as mismatches can lead to reduced power or even inverted signal. Where the appropriate HRF is not known (for example due to potential developmental delay)...

Evaluation of Multiband EPI Acquisitions for Resting State fMRI

Preibisch, Christine; Castrillón G., J. Gabriel; Bührer, Martin; Riedl, Valentin
Fonte: Public Library of Science Publicador: Public Library of Science
Tipo: Artigo de Revista Científica
Publicado em 16/09/2015 Português
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26.84%
Functional magnetic resonance imaging (fMRI) and particularly resting state fMRI (rs-fMRI) is widely used to investigate resting state brain networks (RSNs) on the systems level. Echo planar imaging (EPI) is the state-of-the-art imaging technique for most fMRI studies. Therefore, improvements of EPI might lead to increased sensitivity for a large amount of studies performed every day. A number of developments to shorten acquisition time have been recently proposed and the multiband technique, allowing the simultaneous acquisition of multiple slices yielding an equivalent reduction of measurement time, is the most promising among them. While the prospect to significantly reduce acquisition time by means of high multiband acceleration factors (M) appears tempting, signal quality parameters and the sensitivity to detect common RSNs with increasing M-factor have only been partially investigated up to now. In this study, we therefore acquired rs-fMRI data from 20 healthy volunteers to systematically investigate signal characteristics and sensitivity for brain network activity in datasets with increasing M-factor, M = 2 − 4. Combined with an inplane, sensitivity encoding (SENSE), acceleration factor, S = 2, we applied a maximal acceleration factor of 8 (S2×M4). Our results suggest that an M-factor of 2 (total acceleration of 4) only causes negligible SNR decrease but reveals common RSN with increased sensitivity and stability. Further M-factor increase produced random artifacts as revealed by signal quality measures that may affect interpretation of RSNs under common scanning conditions. Given appropriate hardware...

Alterações da default mode network provocadas pela ingestão de Ayahuasca investigadas por Ressonância Magnética Funcional

Fontes, Fernanda Palhano Xavier de
Fonte: Universidade Federal do Rio Grande do Norte; BR; UFRN; Programa de Pós-Graduação em Neurociencias; Neurobiologia Celular e Molecular; Neurobiologia de Sistemas e Cognição; Neurocomputação Neuroengen Publicador: Universidade Federal do Rio Grande do Norte; BR; UFRN; Programa de Pós-Graduação em Neurociencias; Neurobiologia Celular e Molecular; Neurobiologia de Sistemas e Cognição; Neurocomputação Neuroengen
Tipo: Dissertação Formato: application/pdf
Português
Relevância na Pesquisa
26.84%
Ayahuasca is psychotropic beverage that has been used for ages by indigenous populations in South America, notably in the Amazon region, for religious and medicinal purposes. The tea is obtained by the decoction of leaves from the Psychotria viridis with the bark and stalk of a shrub, the Banisteriopsis caapi. The first is rich in N-N-dimethyltryptamine (DMT), which has an important and well-known hallucinogenic effect due to its agonistic action in serotonin receptors, specifically 5-HT2A. On the other hand, β-carbolines present in B. caapi, particularly harmine and harmaline, are potent monoamine oxidase inhibitors (MAOi). In addition, the tetrahydroharmine (THH), also present in B. caapi, acts as mild selective serotonin reuptake inhibitor and a weak MAOi. This unique composition induces a number of affective, sensitive, perceptual and cognitive changes in individuals under the effect of Ayahuasca. On the other hand, there is growing interest in the Default Mode Network (DMN), which has been consistently observed in functional neuroimaging studies. The key components of this network include structures in the brain midline, as the anterior medial frontal cortex, ventral medial frontal cortex, posterior cingulate cortex, precuneus...

Avaliação por ressonância magnética funcional e estimulação magnética transcraniana da intervenção única da terapia espelho em pacientes após acidente vascular cerebral isquêmico

Novaes, Morgana Menezes
Fonte: Universidade Federal do Rio Grande do Norte; BR; UFRN; Programa de Pós-Graduação em Neurociencias; Neurobiologia Celular e Molecular; Neurobiologia de Sistemas e Cognição; Neurocomputação Neuroengen Publicador: Universidade Federal do Rio Grande do Norte; BR; UFRN; Programa de Pós-Graduação em Neurociencias; Neurobiologia Celular e Molecular; Neurobiologia de Sistemas e Cognição; Neurocomputação Neuroengen
Tipo: Dissertação Formato: application/pdf
Português
Relevância na Pesquisa
26.84%
Mirror therapy (MT) is being used as a rehabilitation tool in various diseases, including stroke. Although some studies have shown its effectiveness, little is known about neural mechanisms that underlie the rehabilitation process. Therefore, this study aimed at assessing cortical neuromodulation after a single MT intervention in ischemic stroke survivors, by means of by functional Magnetic Resonance Imaging (fMRI) and Transcranial Magnetic Stimulation (TMS). Fifteen patients participated in a single thirty minutes MT session. fMRI data was analyzed bilaterally in the following Regions of Interest (ROI): Supplementary Motor Area (SMA), Premotor cortex (PMC), Primary Motor cortex (M1), Primary Sensory cortex (S1) and Cerebellum. In each ROI, changes in the percentage of occupation and beta values were computed. Group fMRI data showed a significant decreased in the percentage of occupation in PMC and cerebellum, contralateral to the affected hand (p <0.05). Significant increase in beta values was observed in the following contralateral motor areas: SMA, Cerebellum, PMC and M1 (p<0,005). Moreover, a significant decrease was observed in the following ipsilateral motor areas: PMC and M1 (p <0,001). In S1 a bilateral significant decrease (p<0.0005) was observed.TMS consisted of the analysis of Motor Evoked Potential (MEP) of M1 hotspot. A significant increase in the amplitude of the MEP was observed after therapy in the group (p<0...

Reproducibility and Temporal Structure in Weekly Resting-State fMRI over a Period of 3.5 Years

Choe, Ann S.; Jones, Craig K.; Joel, Suresh E.; Muschelli, John; Belegu, Visar; Caffo, Brian S.; Lindquist, Martin A.; van Zijl, Peter C. M.; Pekar, James J.
Fonte: Public Library of Science Publicador: Public Library of Science
Tipo: Artigo de Revista Científica
Publicado em 30/10/2015 Português
Relevância na Pesquisa
26.84%
Resting-state functional MRI (rs-fMRI) permits study of the brain’s functional networks without requiring participants to perform tasks. Robust changes in such resting state networks (RSNs) have been observed in neurologic disorders, and rs-fMRI outcome measures are candidate biomarkers for monitoring clinical trials, including trials of extended therapeutic interventions for rehabilitation of patients with chronic conditions. In this study, we aim to present a unique longitudinal dataset reporting on a healthy adult subject scanned weekly over 3.5 years and identify rs-fMRI outcome measures appropriate for clinical trials. Accordingly, we assessed the reproducibility, and characterized the temporal structure of, rs-fMRI outcome measures derived using independent component analysis (ICA). Data was compared to a 21-person dataset acquired on the same scanner in order to confirm that the values of the single-subject RSN measures were within the expected range as assessed from the multi-participant dataset. Fourteen RSNs were identified, and the inter-session reproducibility of outcome measures—network spatial map, temporal signal fluctuation magnitude, and between-network connectivity (BNC)–was high, with executive RSNs showing the highest reproducibility. Analysis of the weekly outcome measures also showed that many rs-fMRI outcome measures had a significant linear trend...

fMRI of Retina-Originated Phosphenes Experienced by Patients with Leber Congenital Amaurosis

Ashtari, Manzar; Cyckowski, Laura; Yazdi, Alborz; Viands, Amanda; Marshall, Kathleen; Bókkon, István; Maguire, Albert; Bennett, Jean
Fonte: Public Library of Science Publicador: Public Library of Science
Tipo: Artigo de Revista Científica
Publicado em 21/01/2014 Português
Relevância na Pesquisa
26.84%
A phenomenon characterized by the experience of seeing light without any light actually entering the eye is called phosphenes or photopsias. Phosphenes can occur spontaneously or via induction by external stimuli. Previous reports regarding phosphenes have primarily focused on externally induced phosphenes such as by applying alternating or direct current to the cortex. A few of these reports used functional magnetic resonance (fMRI) to study activations induced by cortical phosphenes. However, there are no fMRI reports on spontaneous phosphenes originating from the retina and the resulting pattern of cortical activations. We performed fMRI during a reversing checkerboard paradigm in three LCA patients who underwent unilateral gene therapy and reported experiencing frequent phosphene on a daily basis. We observed bilateral cortical activation covering the entire visual cortices when patients reported experiencing phosphenes. In contrast, in the absence of phosphenes, activation was regulated by patient's visual ability and demonstrated improved cortical activation due to gene therapy. These fMRI results illustrate the potential impact of phosphene perception on visual function and they may explain some of the variability that clinicians find in visual function testing in retinal degeneration. Although we did not perform correlations between visual function and phosphenes...

Spatial–temporal modelling of fMRI data through spatially regularized mixture of hidden process models

Shen, Yuan; Mayhew, Stephen D.; Kourtzi, Zoe; Tiňo, Peter
Fonte: Academic Press Publicador: Academic Press
Tipo: Artigo de Revista Científica
Publicado em 01/01/2014 Português
Relevância na Pesquisa
26.84%
Previous work investigated a range of spatio-temporal constraints for fMRI data analysis to provide robust detection of neural activation. We present a mixture-based method for the spatio-temporal modelling of fMRI data. This approach assumes that fMRI time series are generated by a probabilistic superposition of a small set of spatio-temporal prototypes (mixture components). Each prototype comprises a temporal model that explains fMRI signals on a single voxel and the model's “region of influence” through a spatial prior over the voxel space. As the key ingredient of our temporal model, the Hidden Process Model (HPM) framework proposed in Hutchinson et al. (2009) is adopted to infer the overlapping cognitive processes triggered by stimuli. Unlike the original HPM framework, we use a parametric model of Haemodynamic Response Function (HRF) so that biological constraints are naturally incorporated in the HRF estimation. The spatial priors are defined in terms of a parameterised distribution. Thus, the total number of parameters in the model does not depend on the number of voxels. The resulting model provides a conceptually principled and computationally efficient approach to identify spatio-temporal patterns of neural activation from fMRI data...

SMART: A statistical framework for optimal design matrix generation with application to fMRI

Pendse, Gautam; Schwarz, Adam; Baumgartner, Richard; Coimbra, Alexandre; Borsook, David; Becerra, Lino
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 11/03/2009 Português
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26.84%
The general linear model (GLM) is a well established tool for analyzing functional magnetic resonance imaging (fMRI) data. Most fMRI analyses via GLM proceed in a massively univariate fashion where the same design matrix is used for analyzing data from each voxel. A major limitation of this approach is the locally varying nature of signals of interest as well as associated confounds. This local variability results in a potentially large bias and uncontrolled increase in variance for the contrast of interest. The main contributions of this paper are two fold (1) We develop a statistical framework called SMART that enables estimation of an optimal design matrix while explicitly controlling the bias variance decomposition over a set of potential design matrices and (2) We develop and validate a numerical algorithm for computing optimal design matrices for general fMRI data sets. The implications of this framework include the ability to match optimally the magnitude of underlying signals to their true magnitudes while also matching the "null" signals to zero size thereby optimizing both the sensitivity and specificity of signal detection. By enabling the capture of multiple profiles of interest using a single contrast (as opposed to an F-test) in a way that optimizes for both bias and variance enables the passing of first level parameter estimates and their variances to the higher level for group analysis which is not possible using F-tests. We demonstrate the application of this approach to in vivo pharmacological fMRI data capturing the acute response to a drug infusion...

How to test cognitive theory with fMRI

Chatham, Christopher H.; Badre, David
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Português
Relevância na Pesquisa
26.84%
The objective of this chapter is to provide a guide to using functional magnetic resonance imaging (fMRI) to inform cognitive theory. This is, of course, a daunting task, as the premise itself - that fMRI data can inform cognitive theory - is still actively debated. Below, we touch on this debate as a means of framing our guide. In particular, we argue that cognitive theories can be constrained by neuroscientific data, including that offered by fMRI, but to do so requires embellishing the cognitive theory so that it can make predictions for neuroscience; much the same as how testing a cognitive theory using behavior requires embellishing that theory to make experimentally realizable behavioral predictions (i.e., the process of generating operational definitions). Moreover, recent years have seen the development of several new approaches that allow fMRI to better test neurally-embellished models. Along with a review of several ways of testing neurally-embellished cognitive theory using fMRI, we also consider the inferential challenges that can accompany these approaches. Readers of this chapter should gain an understanding of both of the potential power and the challenges associated with fMRI as a cognitive neuroscience methodology.; Comment: 40 pages...

Scale-Free and Multifractal Time Dynamics of fMRI Signals during Rest and Task

Ciuciu, P.; Varoquaux, G.; Abry, P.; Sadaghiani, S.; Kleinschmidt, A.
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 20/08/2013 Português
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26.84%
Scaling temporal dynamics in functional MRI (fMRI) signals have been evidenced for a decade as intrinsic characteristics of ongoing brain activity (Zarahn et al., 1997). Recently, scaling properties were shown to fluctuate across brain networks and to be modulated between rest and task (He, 2011): notably, Hurst exponent, quantifying long memory, decreases under task in activating and deactivating brain regions. In most cases, such results were obtained: First, from univariate (voxelwise or regionwise) analysis, hence focusing on specific cognitive systems such as Resting-State Networks (RSNs) and raising the issue of the specificity of this scale-free dynamics modulation in RSNs. Second, using analysis tools designed to measure a single scaling exponent related to the second order statistics of the data, thus relying on models that either implicitly or explicitly assume Gaussianity and (asymptotic) self-similarity, while fMRI signals may significantly depart from those either of those two assumptions (Ciuciu et al., 2008; Wink et al., 2008). To address these issues, the present contribution elaborates on the analysis of the scaling properties of fMRI temporal dynamics by proposing two significant variations. First, scaling properties are technically investigated using the recently introduced Wavelet Leader-based Multifractal formalism (WLMF; Wendt et al....