139 research outputs found
ADJUST: An automatic EEG artifact detector based on the joint use of spatial and temporal features
No full textA successful method for removing artifacts from electroencephalogram (EEG) recordings is Independent Component
Analysis (ICA), but its implementation remains largely user-dependent. Here, we propose a completely automatic
algorithm (ADJUST) that identifies artifacted independent components by combining stereotyped artifact-specific
spatial and temporal features. Features were optimized to capture blinks, eye movements, and generic discontinuities
on a feature selection dataset. Validation on a totally different EEG dataset shows that (1) ADJUST’s classification of
independent components largely matches a manual one by experts (agreement on 95.2% of the data variance), and (2)
Removal of the artifacted components detected by ADJUST leads to neat reconstruction of visual and auditory event-
related potentials from heavily artifacted data. These results demonstrate that ADJUST provides a fast, efficient, and
automatic way to use ICA for artifact removal
The role of medial prefrontal cortex in processing emotional self-referential information: a combined TMS/fMRI study
No full textIn this study we investigate the neural basis of emotional content in self-referential processing by using a combination of off-line repetitive Transcranial Magnetic Stimulation (rTMS) applied to the medial prefrontal cortex (mPFC) and whole-brain functional Magnetic Resonance Imaging (fMRI).We applied effective or ineffective (sham) 1-Hz rTMS to the mPFC of 14 healthy participants who immediately thereafter underwent fMRI while performing a personality attribution task to self or to others. rTMS produced an increase in the participants’ reaction time (≈ 60 msec) when processing negative attributes. The neuroimaging findings indicated the involvement of a network of cortical nodes distant from those at the stimulation site; these distant nodes showed task-specific changes in blood oxygen level-dependent (BOLD) activity after effective TMS. The posterior cingulate cortex seemingly encoded the negative dimension of stimuli, but it did not differentiate between self or other. On the contrary the left angular gyrus and the left anterior temporal cortex showed changes indicating encoding of negative self-directed categorization. The mPFC region did not show effects of rTMS along the self-other dimension, but only along the affective dimension. The results indicate that the mPFC is a pivotal node in a cortical network that supports affective referential reasoning. Therefore, a key function of mPFC seems to be related to the processing of negative attributes. In the other nodes of the network the two dimensions of self-other attribution and affective attribution are partially independent, but largely overlapping with different degrees of local specialization
Functional and Developmental Significance of Amplitude Variance Asymmetry in the BOLD Resting-State Signal
No full textIt is known that the brain's resting-state activity (RSA) is organized in low frequency oscillations that drive network connectivity. Recent research has also shown that elements of RSA described by high-frequency and nonoscillatory properties are non-random and functionally relevant. Motivated by this research, we investigated nonoscillatory aspects of the blood-oxygen-level-dependent (BOLD) RSA using a novel method for characterizing subtle fluctuation dynamics. The metric that we develop quantifies the relative variance of the amplitude of local-maxima and local-minima in a BOLD time course (amplitude variance asymmetry; AVA). This metric reveals new properties of RSA activity, without relying on connectivity as a descriptive tool. We applied the AVA analysis to data from 3 different participant groups (2 adults, 1 child) collected from 3 different centers. The analyses show that AVA patterns a) identify 3 types of RSA profiles in adults' sensory systems b) differ in topology and pattern of dynamics in adults and children, and c) are stable across magnetic resonance scanners. Furthermore, children with higher IQ demonstrated more adult-like AVA patterns. These findings indicate that AVA reflects important and novel dimensions of brain development and RSA
Theranostic Gold-Magnetite Hybrid Nanoparticles for MRI-guided Radiosensitization
No full textThe main limitation of drug-enhanced radiotherapy concerns the difficulty to evaluate the
effectiveness of cancer targeting after drug administration hindering the standardization of
therapies based on current radiosensitizing compounds. The challenge regards the development
of systems able to combine imaging and radiotherapy enhancement in order to perform highly
reliable cancer theragnosis. For these reasons, gold-magnetite hybrid nanoparticles (H-NPs) are
proposed as innovative theranostic nanotools for imaging-guided radiosensitization in cancer
treatment. In this work we propose a novel method for the synthesis of hydrophilic and
superparamagnetic Tween20-stabilized gold-magnetite H-NPs. Morphology and chemical
composition of nanoparticles were assessed by transmission electron microscopy, x-ray
diffraction analysis and ion-coupled plasma optical emission spectroscopy. Colloidal stability
and magnetic properties of nanoparticles were determined by dynamic light scattering and
magnetometry. The potentialities of H-NPs for magnetic resonance imaging were studied using a
human 4T-MRI scanner. Nanoparticles were proven to induce concentration-dependent contrast
enhancement in T2*-weighted MR-images. The cytotoxicity, the cellular uptake and the
radiosensitization activity of H-NPs were investigated in human osteosarcoma MG63 cell
cultures and murine 3T3 fibroblasts, using specific bioassays and laser scanning confocal
microscopy. H-NPs did not exhibit significant toxicity and were demonstrated to be internalized
by cells. A significant x-ray enhancement at specific H-NPs exposure concentrations was
evidenced on MG63 cell line
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
An investigation of the use of Gradient- and Spin-Echo (GRASE) imaging for functional MRI of the human brain
No full textThis work examines the use of Gradient- and Spin-Echo (GRASE) as an alternative imaging method to EPI for fMRI in brain regions with short T² using a 3Tesla system. The choice of GRASE is motivated by its lower sensitiity to field inhomogeneities compared to EPI and its lower radio-frequency power deposition in comparison with a pure spin-echo imaging method
Harmonization of neuroimaging biomarkers for neurodegenerative diseases: A survey in the imaging community of perceived barriers and suggested actions
No full textIntroduction: Molecular, functional, and structural neuroimaging biomarkers are largely used to study neurodegenerative diseases, but their benefits to patients/science might be greatly enhanced by improving standardization and cross-validation. In this EU Joint Programme-Neurodegenerative Diseases Research–funded project, we surveyed the neuroimaging community to assess perceived barriers in multicentric neuroimaging harmonization and actions to overcome them. Methods: An anonymous survey addressed researchers, clinicians, pharma industry, and professional associations, inquiring about both general and modality-specific harmonization barriers. Results: Survey participants (459) represented an international (37 countries) multidisciplinary community. We identified two sets of funding actions, one proposing the creation of an updated hub of documents to help researchers plan and execute multicentric neuroimaging studies capitalizing from previous studies, and the other focused on modality-specific harmonization challenges in future neurodegenerative diseases clinical trials. Discussion: This large survey of priorities and actions may help define harmonization calls launched by worldwide science funding agencies
Disease Tracking Markers for Alzheimer's Disease at the Prodromal (MCI) Stage
No full textOlder persons with Mild Cognitive Impairment (MCI) feature neurobiological Alzheimer's Disease (AD) in 50% to 70% of the cases and develop dementia within the next 5 to 7 years. Current evidence suggests that biochemical, neuroimaging, electrophysiological, and neuropsychological markers can track the disease over time since the MCI stage (also called prodromal AD). The amount of evidence supporting their validity is of variable strength. We have reviewed the current literature and categorized evidence of validity into three classes: Class A, availability of multiple serial studies; Class B a single serial study or multiple cross sectional studies of patients with increasing disease severity from MCI to probable AD; and class C, multiple cross sectional studies of patients in the dementia stage, not including the MCI stage. Several Class A studies suggest that episodic memory and semantic fluency are the most reliable neuropsychological markers of progression. Hippocampal atrophy, ventricular volume and whole brain atrophy are structural MRI markers with class A evidence. Resting-state fMRI and connectivity, and diffusion MR markers in the medial temporal white matter (parahippocampus and posterior cingulum) and hippocampus are promising but require further validation. Change in amyloid load in MCI patients warrant further investigations, e.g. over longer period of time, to assess its value as marker of disease progression. Several spectral markers of resting state EEG rhythms that might reflect neurodegenerative processes in the prodromal stage of AD (EEG power density, functional coupling, spectral coherence, and synchronization) suffer from lack of appropriately designed studies. Although serial studies on late event-related potentials (ERPs) in healthy elders or MCI patients are inconclusive, others tracking disease progression and effects of cholinesterase inhibiting drugs in AD, and cross-sectional including MCI or predicting development of AD offer preliminary evidence of validity as a marker of disease progression from the MCI stage. CSF Markers, such as A beta(1-42), t-tau and p-tau are valuable markers which support the clinical diagnosis of Alzheimer's disease. However, these markers are not sensitive to disease progression and cannot be used to monitor the severity of Alzheimer's disease. For Isoprostane F2 some evidence exists that its increase correlates with the progression and the severity of AD. RI Jovicich, Jorge/D-2293-201
Structural connectivity of the human anterior temporal lobe: A diffusion magnetic resonance imaging study
No full textThe anterior temporal lobes (ATL) have been implicated in a range of cognitive functions including auditory and visual perception, language, semantic knowledge, and social-emotional processing. However, the anatomical relationships between the ATLs and the broader cortical networks that subserve these functions have not been fully elucidated. Using diffusion tensor imaging (DTI) and probabilistic tractography, we tested the hypothesis that functional segregation of information in the ATLs is reflected by distinct patterns of structural connectivity to regions outside the ATLs. We performed a parcellation of the ATLs bilaterally based on the degree of connectivity of each voxel with eight ipsilateral target regions known to be involved in various cognitive networks. Six discrete segments within each ATL showed preferential connectivity to one of the ipsilateral target regions, via four major fiber tracts (uncinate, inferior longitudinal, middle longitudinal, and arcuate fasciculi). Two noteworthy interhemispheric differences were observed: connections between the ATL and orbito-frontal areas were stronger in the right hemisphere, while the consistency of the connection between the ATL and the inferior frontal gyrus through the arcuate fasciculus was greater in the left hemisphere. Our findings support the hypothesis that distinct regions within the ATLs have anatomical connections to different cognitive networks. Hum Brain Mapp 37:2210-2222, 2016. © 2016 Wiley Periodicals, Inc
Neural basis for priming of pop-out during visual search revealed with fMRI
No full textMalikovic and Nakayama first showed that visual search efficiency can be influenced by priming effects. Even "pop-out" targets (defined by unique color) are judged quicker if they appear at the same location and/or in the same color as on the preceding trial, in an unpredictable sequence. Here, we studied the potential neural correlates of such priming in human visual search using functional magnetic resonance imaging (fMRI). We found that repeating either the location or the color of a singleton target led to repetition suppression of blood oxygen level-dependent (BOLD) activity in brain regions traditionally linked with attentional control, including bilateral intraparietal sulci. This indicates that the attention system of the human brain can be "primed," in apparent analogy to repetition-suppression effects on activity in other neural systems. For repetition of target color but not location, we also found repetition suppression in inferior temporal areas that may be associated with color processing, whereas repetition of target location led to greater reduction of activation in contralateral inferior parietal and frontal areas, relative to color repetition. The frontal eye fields were also implicated, notably when both target properties (color and location) were repeated together, which also led to further BOLD decreases in anterior fusiform cortex not seen when either property was repeated alone. These findings reveal the neural correlates for priming of pop-out search, including commonalities, differences, and interactions between location and color repetition. fMRI repetition-suppression effects may arise in components of the attention network because these settle into a stable 1. attractor state" more readily when the same target property is repeated than when a different attentional state is required
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