1,720,980 research outputs found
Gradient Artifact Removal in Co-registration EEG/fMRI
No full textIn this work we present a novel method to remove the gradient artifact in co-registered EEG/fMRI, of wide applicability and able to preserve EEG integrity. It is based on an iterative subtraction, but it improves upon exiting methods since for each slice the amplitude of the gradient templates to be subtracted is optimally adjusted by linear regression. This avoids the need of adaptive noise cancellation, or principal component analysis. Performance of this algorithm was first evaluated on both in silico and real data. Results indicate that few iterations are needed for a successful gradient removal, without compromising frequency content of EEG
Behavioral and neurophysiological effects of repetitive transcranial magnetic stimulation on the minimally conscious state: a case study
No full textBACKGROUND: In 2007, Schiff et al reported a patient in a minimally conscious state (MCS) who responded to deep brain stimulation (DBS), but clinicians cannot predict which patients might respond prior to the implantation of electrodes.
METHODS: A patient in a MCS for 5 years participated in an ABA design alternating between repetitive transcranial magnetic stimulation (rTMS) and peripheral nerve stimulation. rTMS (condition A) involved the delivery of 10 trains of 100 stimuli at 20 Hz using a stimulator with a 70-mm figure-of-eight coil to elicit a contraction of the abductor pollicis brevis. Condition B used median nerve electrical stimulation.
RESULTS: After peripheral stimulation, the patient did not exhibit clinical, behavioral, or electroencephalographic (EEG) changes. The frequency of specific and meaningful behaviors increased after rTMS, along with the absolute and relative power of the EEG δ, β, and α bands.
CONCLUSION: These results suggest that rTMS may improve awareness and arousal in MCS. If these results are reproducible, rTMS may identify subgroups of MCS patients who might benefit from DBS
Effect of voluntary repetitive long-lasting muscle contraction activity on the BOLD signal as assessed by optimal hemodynamic response function.
No full textAbstract
OBJECTIVE:
Among other neuroimaging techniques, functional magnetic resonance imaging (fMRI) can be useful for studying the development of motor fatigue. The aim of this study was to identify differences in cortical neuronal activation in nine subjects on three motor tasks: right-hand movement with minimum, maximum, and post-fatigue maximum finger flexion.
MATERIALS AND METHODS:
fMRI activation maps for each subject and during each condition were obtained by estimating the optimal model of the hemodynamic response function (HRF) out of four standard HRF models and an individual-based HRF model (ibHRF).
RESULTS:
ibHRF was selected as the optimal model in six out of nine subjects for minimum movement, in five out of nine for maximum movement, and in eight out of nine for post-fatigue maximum movement. As compared to maximum movement, a large reduction in the total number of active voxels (primary sensorimotor area, supplementary motor area and cerebellum) was observed in post-fatigue maximum movement.
CONCLUSION:
This is the first approach to the evaluation of long-lasting contraction effort in healthy subjects by means of the fMRI paradigm with the use of an individual-based hemodynamic response. The results may be relevant for defining a baseline in future studies on central fatigue in patients with neuropathological disorders
Noise removal in resting-state and task fMRI: functional connectivity and activation maps
Full text linkOBJECTIVE: BOLD-based fMRI is a widely used non-invasive tool for mapping brain function and connectivity. However, the BOLD signal is highly affected by non-neuronal contributions arising from head motion, physiological noise and scanner artefacts. Therefore, it is necessary to recover the signal of interest from the other noise-related fluctuations to obtain reliable functional connectivity results. Several pre-processing pipelines have been developed, mainly based on nuisance regression and ICA. The aim of this work was to investigate the impact of seven widely used denoising methods on both resting-state and task fMRI. APPROACH: Task-fMRI can provide some ground truth given that the task administered has well established brain activations. The resulting cleaned data were compared using a wide range of measures: motion evaluation and data quality, resting-state networks and task activations, functional connectivity. RESULTS: Improved signal quality and reduced motion artefacts were obtained with all advanced pipelines, compared to the minimally pre-processed data. Larger variability was observed in the case of brain activation and functional connectivity estimates, with ICA-based pipelines generally achieving more reliable and accurate results. SIGNIFICANCE: This work provides an evidence-based reference for investigators to choose the most appropriate method for their study and data
Integrating EEG and fMRI in epilepsy.
No full text. Here, we present an easy-to-use and automatic approach for combined EEG-fMRI analysis able to improve IEDs identification based on Independent Component Analysis and wavelet analysis. EEG signal due to IED is reconstructed and its wavelet power is used as a regressor in GLM. The method was validated on simulated data and then applied on real data set consisting of 2 normal subjects and 5 patients with partial epilepsy. In all continuous EEG-fMRI recording sessions a good quality EEG was obtained allowing the detection of spontaneous IEDs and the analysis of the related BOLD activation
Can DTI and 3D-SHORE based indices differentiate RRMS from PMS Patients?
No full textMultiple Sclerosis (MS) is a long-lasting disease of the brain and spinal cord, characterized by demyelinating lesions in white matter (WM) as well as cortical lesions and tissue volume loss in several grey matter (GM) structures. Although GM alterations are a common feature of MS, they have not been largely explored in literature. Diffusion Tensor Imaging (DTI) is nowadays used to investigate the damaged WM structures in MS since DTI-based indices, as Fractional Anisotropy (FA) and Mean Diffusivity (MD), have been proven to reflect the pathological features of the disease in many studies. However, DTI has been scarcely employed for GM analysis plus is not able to model the complex fiber architecture. Hence, advanced models are required to probe the microstructural pathology. One of this, the Simple Harmonic Oscillator Based Reconstruction and Estimation (SHORE), is a novel diffusion-weighted Magnetic Resonance Imaging (dMRI) analysis method which is considered a promising tool to characterize tissue microstructure thanks to its ability to detect multiple diffusion directions. In this study, we aimed to probe the viability of DTI and 3D-SHORE derived indices for characterizing the microstructural GM modulations in Relapsing Remitting Multiple Sclerosis (RRMS) and Progressive Multiple Sclerosis (PMS) patients by relying on histogram-based analyses
How are BOLD Measures and Connectivity Affected by Noise Removal in Resting-state and Task fMRI
No full textFunctional magnetic resonance imaging (fMRI), based on blood-oxygenated-level dependent (BOLD) contrast, is a powerful non-invasive tool to assess brain function and connectivity in vivo. However, as BOLD signals are noisy, properly recovering the signal of interest from noise-related uctuations is essential to obtain reliable measures. To this end, several pre-processing pipelines have been developed, mainly adopting nuisance regression and independent component analysis (ICA). While previous works assessed the impact of these cleaning methods on resting-state fMRI (rs-fMRI) time-series and focused on specic aspects of signal cleaning (e.g. motion removal), their wider effect on both resting-state and task fMRI is yet to be fully investigated. In this work, we aimed to assess the inuence of different pre-processing methods on BOLD measures, by considering a rs-fMRI dataset, where no a priori information regarding which brain areas are expected to be active is present, and a task fMRI dataset, for which there is a strong hypothesis regarding active brain areas
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
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