Página 1 dos resultados de 13 itens digitais encontrados em 0.000 segundos

Frequency Domain Connectivity Identification: An Application of Partial Directed Coherence in fMRI

SATO, Joao R.; TAKAHASHI, Daniel Y.; ARCURI, Silvia M.; Sameshima, Koichi; MORETTIN, Pedro A.; Baccala, Luiz Antonio
Fonte: WILEY-LISS Publicador: WILEY-LISS
Tipo: Artigo de Revista Científica
Português
Relevância na Pesquisa
27.62%
Functional magnetic resonance imaging (fMRI) has become an important tool in Neuroscience due to its noninvasive and high spatial resolution properties compared to other methods like PET or EEG. Characterization of the neural connectivity has been the aim of several cognitive researches, as the interactions among cortical areas lie at the heart of many brain dysfunctions and mental disorders. Several methods like correlation analysis, structural equation modeling, and dynamic causal models have been proposed to quantify connectivity strength. An important concept related to connectivity modeling is Granger causality, which is one of the most popular definitions for the measure of directional dependence between time series. In this article, we propose the application of the partial directed coherence (PDC) for the connectivity analysis of multisubject fMRI data using multivariate bootstrap. PDC is a frequency domain counterpart of Granger causality and has become a very prominent tool in EEG studies. The achieved frequency decomposition of connectivity is useful in separating interactions from neural modules from those originating in scanner noise, breath, and heart beating. Real fMRI dataset of six subjects executing a language processing protocol was used for the analysis of connectivity. Hum Brain Mapp 30:452-461...

Integrating VBM into the General Linear Model with Voxelwise Anatomical Covariates

Oakes, Terrence R.; Fox, Andrew S.; Johnstone, Tom; Chung, Moo K.; Kalin, Ned; Davidson, Richard J.
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Português
Relevância na Pesquisa
16.9%
A current limitation for imaging of brain function is the potential confound of anatomical differences or registration error, which may manifest via apparent functional “activation” for between-subject analyses. With respect to functional activations, underlying tissue mismatches can be regarded as a nuisance variable. We propose adding the probability of gray matter at a given voxel as a covariate (nuisance variable) in the analysis of voxelwise multisubject functional data using standard statistical techniques. A method is presented to assess the extent to which a functional activation can reliably be explained by underlying anatomical differences, and simultaneously, to assess the component of the functional activation which cannot be attributed to anatomical difference and thus is likely due to functional difference alone. Extension of the method to other intermodal imaging applications is discussed. Two exemplary data sets, one PET and one fMRI, are used to demonstrate the implementation and utility of this method, which apportions the relative contributions of anatomy and function for an apparent functional activation. The examples show two distinct types of results. First, a so-called functional activation may actually be caused by a systematic anatomical difference which...

Fluid Registration of Diffusion Tensor Images Using Information Theory

Chiang, Ming-Chang; Leow, Alex D.; Klunder, Andrea D.; Dutton, Rebecca A.; Barysheva, Marina; Rose, Stephen E.; McMahon, Katie L.; de Zubicaray, Greig I.; Toga, Arthur W.; Thompson, Paul M.
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em /04/2008 Português
Relevância na Pesquisa
16.9%
We apply an information-theoretic cost metric, the symmetrized Kullback-Leibler (sKL) divergence, or J-divergence, to fluid registration of diffusion tensor images. The difference between diffusion tensors is quantified based on the sKL-divergence of their associated probability density functions (PDFs). Three-dimensional DTI data from 34 subjects were fluidly registered to an optimized target image. To allow large image deformations but preserve image topology, we regularized the flow with a large-deformation diffeomorphic mapping based on the kinematics of a Navier-Stokes fluid. A driving force was developed to minimize the J-divergence between the deforming source and target diffusion functions, while reorienting the flowing tensors to preserve fiber topography. In initial experiments, we showed that the sKL-divergence based on full diffusion PDFs is adaptable to higher-order diffusion models, such as high angular resolution diffusion imaging (HARDI). The sKL-divergence was sensitive to subtle differences between two diffusivity profiles, showing promise for nonlinear registration applications and multisubject statistical analysis of HARDI data.

Exploratory fMRI Analysis without Spatial Normalization

Lashkari, Danial; Golland, Polina
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em //2009 Português
Relevância na Pesquisa
16.9%
We present an exploratory method for simultaneous parcellation of multisubject fMRI data into functionally coherent areas. The method is based on a solely functional representation of the fMRI data and a hierarchical probabilistic model that accounts for both inter-subject and intra-subject forms of variability in fMRI response. We employ a Variational Bayes approximation to fit the model to the data. The resulting algorithm finds a functional parcellation of the individual brains along with a set of population-level clusters, establishing correspondence between these two levels. The model eliminates the need for spatial normalization while still enabling us to fuse data from several subjects. We demonstrate the application of our method on a visual fMRI study.

Multisubject Learning for Common Spatial Patterns in Motor-Imagery BCI

Devlaminck, Dieter; Wyns, Bart; Grosse-Wentrup, Moritz; Otte, Georges; Santens, Patrick
Fonte: Hindawi Publishing Corporation Publicador: Hindawi Publishing Corporation
Tipo: Artigo de Revista Científica
Português
Relevância na Pesquisa
27.99%
Motor-imagery-based brain-computer interfaces (BCIs) commonly use the common spatial pattern filter (CSP) as preprocessing step before feature extraction and classification. The CSP method is a supervised algorithm and therefore needs subject-specific training data for calibration, which is very time consuming to collect. In order to reduce the amount of calibration data that is needed for a new subject, one can apply multitask (from now on called multisubject) machine learning techniques to the preprocessing phase. Here, the goal of multisubject learning is to learn a spatial filter for a new subject based on its own data and that of other subjects. This paper outlines the details of the multitask CSP algorithm and shows results on two data sets. In certain subjects a clear improvement can be seen, especially when the number of training trials is relatively low.

Changes in clearance, volume and bioavailability of immunosuppressants when given with HAART in HIV-1 infected liver and kidney transplant recipients

Frassetto, L.A.; Floren, L.C.; Barin, B.; Browne, M.; Wolfe, A.R.; Roland, M.E.; Stock, P.G.; Carlson, L.; Christians, U.; Benet, L.Z.
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Português
Relevância na Pesquisa
16.9%
Solid organ transplantation in Human Immunodeficiency Virus 1 (HIV)-infected individuals requiring concomitant use of immunosuppressants (IS) [e.g., cyclosporine (CsA) or tacrolimus (TAC)] and antiretrovirals (ARVs) [e.g., protease inhibitors (PIs) and/or non-nucleoside reverse transcriptase inhibitors (NNRTIs)] is complicated by significant drug interactions. We describe the pharmacokinetics of CsA and TAC in 52 patients on both IS and NNRTIs, PIs, or combined NNRTIs+PIs, in studies conducted at 2 weeks, 3, 6, 12 and 24 months after transplantation. CsA and TAC blood concentrations were measured by LC/MS/MS. This multisubject, varied ARV-IS drug combination, longitudinal observational patient study provided a unique opportunity to examine the effect of different ARV drugs on IS PK by comparing ratios of parameters over time and between PK parameters. Subjects taking concomitant PIs exhibited increases in CsA and TAC exposure (AUC/dose) due to increased apparent oral bioavailability and decreased apparent oral clearance. Those subjects taking CsA and concomitant efavirenz (EFV) showed time dependent increases in exposure due to ~30% increases in apparent oral bioavailability over time as well as decreased apparent oral clearance, while subjects on TAC and EFV showed time-dependent changes in all PK parameters. The increased bioavailability was not observed in patients on CsA and nevirapine (NVP). These differences between IS drugs and the changes in PK parameters are not easily predicted...

Irrational exuberance and neural crash warning signals during endogenous experimental market bubbles

Smith, Alec; Lohrenz, Terry; King, Justin; Montague, P. Read; Camerer, Colin F.
Fonte: National Academy of Sciences Publicador: National Academy of Sciences
Tipo: Artigo de Revista Científica
Português
Relevância na Pesquisa
16.9%
Asset price bubbles are an important example of human group decision making gone awry, but the behavioral and neural underpinnings of bubble dynamics remain mysterious. In multisubject markets determined by 11–23 subjects, with 2–3 subjects simultaneously scanned using functional MRI, we show how behavior and brain activity interact during bubbles. Nucleus accumbens (NAcc) activity tracks the price bubble and predicts future price changes. Traders who buy more aggressively based on NAcc signals earn less. High-earning traders have early warning signals in the anterior insular cortex before prices reach a peak, and sell coincidently with that signal, precipitating the crash. These experiments could help understand other cases in which human groups badly miscompute the value of actions or events.

A Computationally Efficient, Exploratory Approach to Brain Connectivity Incorporating False Discovery Rate Control, A Priori Knowledge, and Group Inference

Liu, Aiping; Li, Junning; Wang, Z. Jane; McKeown, Martin J.
Fonte: Hindawi Publishing Corporation Publicador: Hindawi Publishing Corporation
Tipo: Artigo de Revista Científica
Português
Relevância na Pesquisa
16.9%
Graphical models appear well suited for inferring brain connectivity from fMRI data, as they can distinguish between direct and indirect brain connectivity. Nevertheless, biological interpretation requires not only that the multivariate time series are adequately modeled, but also that there is accurate error-control of the inferred edges. The PCfdr algorithm, which was developed by Li and Wang, was to provide a computationally efficient means to control the false discovery rate (FDR) of computed edges asymptotically. The original PCfdr algorithm was unable to accommodate a priori information about connectivity and was designed to infer connectivity from a single subject rather than a group of subjects. Here we extend the original PCfdr algorithm and propose a multisubject, error-rate-controlled brain connectivity modeling approach that allows incorporation of prior knowledge of connectivity. In simulations, we show that the two proposed extensions can still control the FDR around or below a specified threshold. When the proposed approach is applied to fMRI data in a Parkinson's disease study, we find robust group evidence of the disease-related changes, the compensatory changes, and the normalizing effect of L-dopa medication. The proposed method provides a robust...

Emotions promote social interaction by synchronizing brain activity across individuals

Nummenmaa, Lauri; Glerean, Enrico; Viinikainen, Mikko; Jääskeläinen, Iiro P.; Hari, Riitta; Sams, Mikko
Fonte: National Academy of Sciences Publicador: National Academy of Sciences
Tipo: Artigo de Revista Científica
Português
Relevância na Pesquisa
16.9%
Sharing others’ emotional states may facilitate understanding their intentions and actions. Here we show that networks of brain areas “tick together” in participants who are viewing similar emotional events in a movie. Participants’ brain activity was measured with functional MRI while they watched movies depicting unpleasant, neutral, and pleasant emotions. After scanning, participants watched the movies again and continuously rated their experience of pleasantness–unpleasantness (i.e., valence) and of arousal–calmness. Pearson’s correlation coefficient was used to derive multisubject voxelwise similarity measures [intersubject correlations (ISCs)] of functional MRI data. Valence and arousal time series were used to predict the moment-to-moment ISCs computed using a 17-s moving average. During movie viewing, participants' brain activity was synchronized in lower- and higher-order sensory areas and in corticolimbic emotion circuits. Negative valence was associated with increased ISC in the emotion-processing network (thalamus, ventral striatum, insula) and in the default-mode network (precuneus, temporoparietal junction, medial prefrontal cortex, posterior superior temporal sulcus). High arousal was associated with increased ISC in the somatosensory cortices and visual and dorsal attention networks comprising the visual cortex...

Mental Action Simulation Synchronizes Action–Observation Circuits across Individuals

Nummenmaa, Lauri; Smirnov, Dmitry; Lahnakoski, Juha M.; Glerean, Enrico; Jääskeläinen, Iiro P.; Sams, Mikko; Hari, Riitta
Fonte: Society for Neuroscience Publicador: Society for Neuroscience
Tipo: Artigo de Revista Científica
Publicado em 15/01/2014 Português
Relevância na Pesquisa
16.9%
A frontoparietal action–observation network (AON) has been proposed to support understanding others' actions and goals. We show that the AON “ticks together” in human subjects who are sharing a third person's feelings. During functional magnetic resonance imaging, 20 volunteers watched movies depicting boxing matches passively or while simulating a prespecified boxer's feelings. Instantaneous intersubject phase synchronization (ISPS) was computed to derive multisubject voxelwise similarity of hemodynamic activity and inter-area functional connectivity. During passive viewing, subjects' brain activity was synchronized in sensory projection and posterior temporal cortices. Simulation induced widespread increase of ISPS in the AON (premotor, posterior parietal, and superior temporal cortices), primary and secondary somatosensory cortices, and the dorsal attention circuits (frontal eye fields, intraparietal sulcus). Moreover, interconnectivity of these regions strengthened during simulation. We propose that sharing a third person's feelings synchronizes the observer's own brain mechanisms supporting sensations and motor planning, thereby likely promoting mutual understanding.

Synchronous brain activity across individuals underlies shared psychological perspectives

Lahnakoski, Juha M.; Glerean, Enrico; Jääskeläinen, Iiro P.; Hyönä, Jukka; Hari, Riitta; Sams, Mikko; Nummenmaa, Lauri
Fonte: Academic Press Publicador: Academic Press
Tipo: Artigo de Revista Científica
Publicado em 15/10/2014 Português
Relevância na Pesquisa
16.9%
For successful communication, we need to understand the external world consistently with others. This task requires sufficiently similar cognitive schemas or psychological perspectives that act as filters to guide the selection, interpretation and storage of sensory information, perceptual objects and events. Here we show that when individuals adopt a similar psychological perspective during natural viewing, their brain activity becomes synchronized in specific brain regions. We measured brain activity with functional magnetic resonance imaging (fMRI) from 33 healthy participants who viewed a 10-min movie twice, assuming once a ‘social’ (detective) and once a ‘non-social’ (interior decorator) perspective to the movie events. Pearson's correlation coefficient was used to derive multisubject voxelwise similarity measures (inter-subject correlations; ISCs) of functional MRI data. We used k-nearest-neighbor and support vector machine classifiers as well as a Mantel test on the ISC matrices to reveal brain areas wherein ISC predicted the participants' current perspective. ISC was stronger in several brain regions—most robustly in the parahippocampal gyrus, posterior parietal cortex and lateral occipital cortex—when the participants viewed the movie with similar rather than different perspectives. Synchronization was not explained by differences in visual sampling of the movies...

Irrational exuberance and neural crash warning signals during endogenous experimental market bubbles

Smith, Alec; Lohrenz, Terry; King, Justin; Montague, P. Read; Camerer, Colin F.
Fonte: National Academy of Sciences Publicador: National Academy of Sciences
Tipo: Article; PeerReviewed Formato: application/pdf; application/pdf
Publicado em 22/07/2014 Português
Relevância na Pesquisa
16.9%
Groups of humans routinely misassign value to complex future events, especially in settings involving the exchange of resources. If properly structured, experimental markets can act as excellent probes of human group-level valuation mechanisms during pathological overvaluations—price bubbles. The connection between the behavioral and neural underpinnings of such phenomena has been absent, in part due to a lack of enabling technology. We used a multisubject functional MRI paradigm to measure neural activity in human subjects participating in experimental asset markets in which endogenous price bubbles formed and crashed. Although many ideas exist about how and why such bubbles may form and how to identify them, our experiment provided a window on the connection between neural responses and behavioral acts (buying and selling) that created the bubbles. We show that aggregate neural activity in the nucleus accumbens (NAcc) tracks the price bubble and that NAcc activity aggregated within a market predicts future price changes and crashes. Furthermore, the lowest-earning subjects express a stronger tendency to buy as a function of measured NAcc activity. Conversely, we report a signal in the anterior insular cortex in the highest earners that precedes the impending price peak...

Rio Tamanduateí - nascente à foz: percepções da paisagem e processos participativos; Tamanduateí river - spring to its estuary: landscapes's perceptios and parcipatory process

Ramalho, Daniela
Fonte: Universidade de São Paulo. Faculdade de Arquitetura e Urbanismo Publicador: Universidade de São Paulo. Faculdade de Arquitetura e Urbanismo
Tipo: info:eu-repo/semantics/article; info:eu-repo/semantics/publishedVersion; Formato: application/pdf
Publicado em 31/12/2007 Português
Relevância na Pesquisa
16.9%
This article was based on a dissertation of PHD - thesis submitted to evaluation at University of Architecture and Urbanism of São Paulo State. This proposes to analyze the landscape architect’s contribution to the preservation of Fluvial Landscape. The methodology applied was the “Research-Action”, witch inspired a theorical and empiric thesis that resulted in several work sections with community’s leaders, members of public and private institutions and educational and non governmental organizations. The gain products were two landscape projects in public areas and a documentary video that registrate the whole process of participation, perception and action looking forward the preservation of Tamanduatey’s River spring to its estuary.; Este artigo foi baseado na dissertação de mestrado defendida na FAU-USP e busca a contribuição do arquiteto paisagista na preservação das Paisagens Fluviais Urbanas. A metodologia adotada foi a pesquisa-ação, a qual norteou um embasamento teórico e empírico que resultou na aplicação de oficinas em representantes das comunidades envolvidas, além de representantes dos setores públicos, privados, não-governamentais e instituições de ensino. Os produtos resultantes das oficinas foram dois projetos de paisagismo em áreas públicas e um vídeo documentário com o registro de todo o processo participativo de percepção e ação na preservação das paisagens fluviais da nascente à foz do Rio Tamanduateí.