502 research outputs found
Pathogen Management in Surface Waters: Practical Considerations for Reducing Public Health Risk
Resting state MEG oscillations show long-range temporal correlations of phase synchrony that break down during finger movement
The capacity of the human brain to interpret and respond to multiple temporal scales in its surroundings suggests that its internal interactions must also be able to operate over a broad temporal range. In this paper, we utilize a recently introduced method for characterizing the rate of change of the phase difference between MEG signals and use it to study the temporal structure of the phase interactions between MEG recordings from the left and right motor cortices during rest and during a finger-tapping task. We use the Hilbert transform to estimate moment-to-moment fluctuations of the phase difference between signals. After confirming the presence of scale-invariance we estimate the Hurst exponent using detrended fluctuation analysis (DFA). An exponent of >0.5 is indicative of long-range temporal correlations (LRTCs) in the signal. We find that LRTCs are present in the α/μ and β frequency bands of resting state MEG data. We demonstrate that finger movement disrupts LRTCs correlations, producing a phase relationship with a structure similar to that of Gaussian white noise. The results are validated by applying the same analysis to data with Gaussian white noise phase difference, recordings from an empty scanner and phase-shuffled time series. We interpret the findings through comparison of the results with those we obtained from an earlier study during which we adopted this method to characterize phase relationships within a Kuramoto model of oscillators in its sub-critical, critical, and super-critical synchronization states. We find that the resting state MEG from left and right motor cortices shows moment-to-moment fluctuations of phase difference with a similar temporal structure to that of a system of Kuramoto oscillators just prior to its critical level of coupling, and that finger tapping moves the system away from this pre-critical state toward a more random state
Factors Dictating Carbene Formation at (PNP)Ir
The mechanistic subtleties involved with the interaction of an amido/bis(phosphine)-supported (PNP)Ir fragment with a series of linear and cyclic ethers have been investigated using density functional theory. Our analysis has revealed the factors dictating reaction direction toward either an iridium-supported carbene or a vinyl ether adduct. The (PNP)Ir structure will allow carbene formation only from accessible carbons α to the ethereal oxygen, such that d electron back-donation from the metal to the carbene ligand is possible. Should these conditions be unavailable, the main competing pathway to form vinyl ether can occur, but only if the (PNP)Ir framework does not sterically interfere with the reacting ether. In situations where steric hindrance prevents unimpeded access to both pathways, the reaction may progress to the initial C−H activation but no further. Our mechanistic analysis is density functional independent and whenever possible confirmed experimentally by trapping intermediate species experimentally. We have also highlighted an interesting systematic error present in the DFT analysis of reactions where steric environment alters considerably within a reaction
A multi-modal approach to functional neuroimaging
The work undertaken involves the use of functional magnetic resonance imaging (fMRI) and magnetoencephalography (MEG) as separate but complementary non-invasive functional brain imaging modalities. The aim in combining fMRI and MEG is centred around exploitation of the high temporal resolution available in MEG, and the high spatial resolution available in fMRI. However, whilst MEG represents a direct measure of neuronal activity, BOLD fMRI is an indirect measure and this makes the two modalities truly complementary. In both cases, the imaging signals measured are relatively poorly understood and so the fundamental question asked here is: How are the neuromagnetic effects detectable using MEG related to the metabolic effects reflected in the fMRI BOLD response?
Initially, a novel technique is introduced for the detection and spatial localisation of neuromagnetic effects in MEG. This technique, based on a beamforming approach to the MEG inverse problem, is shown to yield accurate results both in simulation and using experimental data. The technique introduced is applied to MEG data from a simple experiment involving stimulation of the visual cortex. A number of heterogeneous neuromagnetic effects are shown to be detectable, and furthermore, these effects are shown to be spatially and temporally correlated with the fMRI BOLD response. The limitations to comparing only two measures of brain activity are discussed, and the use of arterial spin labelling (ASL) to make quantitative measurements of physiological parameters supplementing these two initial metrics is introduced. Finally, a novel technique for accurate quantification of arterial cerebral blood volume using ASL is described and shown to produce accurate results. A concluding chapter then speculates on how these aCBV measurements might be combined with those from MEG in order to better understand the fMRI BOLD response
The relationship between MEG and fMRI
In recent years functional neuroimaging techniques such as fMRI, MEG, EEG and PET have provided researchers with a wealth of information on human brain function. However none of these modalities can measure directly either the neuro-electrical or neuro-chemical processes that mediate brain function. This means that metrics directly reflecting brain ‘activity’ must be inferred from other metrics (e.g. magnetic fields (MEG) or haemodynamics (fMRI)). To overcome this limitation, many studies seek to combine multiple complementary modalities and an excellent example of this is the combination of MEG (which has high temporal resolution) with fMRI (which has high spatial resolution). However, the full potential of multi-modal approaches can only be truly realised in cases where the relationship between metrics is known. In this paper, we explore the relationship between measurements made using fMRI and MEG. We describe the origins of the two signals as well as their relationship to electrophysiology. We review multiple studies that have attempted to characterise the spatial relationship between fMRI and MEG, and we also describe studies that exploit the rich information content of MEG to explore differing relationships between MEG and fMRI across neural oscillatory frequency bands. Monitoring the brain at “rest” has become of significant recent interest to the neuroimaging community and we review recent evidence comparing MEG and fMRI metrics of functional connectivity. A brief discussion of the use of magnetic resonance spectroscopy (MRS) to probe the relationship between MEG/fMRI and neurochemistry is also given. Finally, we highlight future areas of interest and offer some recommendations for the parallel use of fMRI and MEG
Iron therapy in inflammatory bowel disease
© 2020 The Authors. Published by MDPI. This is an open access article available under a Creative Commons licence. The published version can be accessed at the following link on the publisher’s website: https://doi.org/10.3390/nu12113478The most common complication seen in inflammatory bowel disease (IBD) patients is iron deficiency anaemia (IDA). Symptoms such as chronic fatigue can be as debilitating to IBD patients as pathological symptoms of abdominal pain and diarrhoea. Recognising and correcting anaemia may be as important as managing IBD symptoms and improving overall quality of life. Thus, iron replacement should be commenced the moment IDA is identified. Although intravenous iron is now considered standard treatment for IBD patients in Europe, oral iron still appears to be the preferred option. Advantages of oral iron include greater availability, lower costs and ease of applicability. However, its multitude of side effects, impact on the microbiome and further exacerbating IBD activity can have consequences on patient compliance. The newer oral iron formulations show promising safety and efficacy data with a good side effect profile. Intravenous iron formulations bypass the gastrointestinal tract absorption thereby leading to less side effects. Multiple studies have shown its superiority compared to oral formulations although its risk for hypersensitivity reactions continue to lead to clinician hesitancy in prescribing this formulation. This article provides an updated review on diagnosis and management of IDA in IBD patients, discussing the newer oral and intravenous formulations.Published versio
A multi-modal approach to functional neuroimaging
The work undertaken involves the use of functional magnetic resonance imaging (fMRI) and magnetoencephalography (MEG) as separate but complementary non-invasive functional brain imaging modalities. The aim in combining fMRI and MEG is centred around exploitation of the high temporal resolution available in MEG, and the high spatial resolution available in fMRI. However, whilst MEG represents a direct measure of neuronal activity, BOLD fMRI is an indirect measure and this makes the two modalities truly complementary. In both cases, the imaging signals measured are relatively poorly understood and so the fundamental question asked here is: How are the neuromagnetic effects detectable using MEG related to the metabolic effects reflected in the fMRI BOLD response?
Initially, a novel technique is introduced for the detection and spatial localisation of neuromagnetic effects in MEG. This technique, based on a beamforming approach to the MEG inverse problem, is shown to yield accurate results both in simulation and using experimental data. The technique introduced is applied to MEG data from a simple experiment involving stimulation of the visual cortex. A number of heterogeneous neuromagnetic effects are shown to be detectable, and furthermore, these effects are shown to be spatially and temporally correlated with the fMRI BOLD response. The limitations to comparing only two measures of brain activity are discussed, and the use of arterial spin labelling (ASL) to make quantitative measurements of physiological parameters supplementing these two initial metrics is introduced. Finally, a novel technique for accurate quantification of arterial cerebral blood volume using ASL is described and shown to produce accurate results. A concluding chapter then speculates on how these aCBV measurements might be combined with those from MEG in order to better understand the fMRI BOLD response
The Brief Memory and Executive Test (BMET) for detecting vascular cognitive impairment in small vessel disease: a validation study
Background: Cognitive impairment is common in patients with cerebral small vessel disease, but is not well
detected using common cognitive screening tests which have been primarily devised for cortical dementias. We
developed the Brief Memory and Executive Test (BMET); a rapid screening measure sensitive to the impaired
executive function and processing speed characteristic of small vessel disease (SVD). To assess the BMET’s validity
for general use, we evaluated it when administered by non-psychologists in a multicentre study and collected
control data to derive normative scores.
Methods: Two-hundred participants with SVD, defined as a clinical lacunar stroke and a corresponding lacunar
infarct on MRI, and 303 healthy controls aged between 40–90 years old were recruited. The BMET, as well as the
Montreal Cognitive Assessment (MoCA) and Mini Mental State Examination (MMSE), were performed. Overall, 55
SVD participants underwent repeat testing at 3 months to assess the BMET test-retest reliability.
Results: Administering the BMET took a mean (SD) of 12.9 (4.7) in cases and 9.5 (2.6) minutes in controls. Receiver
Operator Curve analysis showed the BMET was a good predictor of cognitive impairment in SVD (AUC = 0.94) and
performed significantly better than both the MoCA (AUC = 0.77) and the MMSE (AUC = 0.70). Using a cut-off score
of 13, the BMET had a sensitivity of 93% and specificity of 76% for detecting cognitive impairment in SVD.
Conclusions: The BMET is a brief and sensitive tool for the detection of cognitive impairment in patients with SVD.The BMET study was funded by The Stroke Association (TSA2010/08). Recruitment to BMET was supported by the NIHR Stroke Clinical Research Network. Hugh Markus is supported by an NIHR Senior Investigator award and his work is supported by the Cambridge University Hospitals NIHR Comprehensive BRC. Matthew Hollocks is supported by a Stroke Association/British Heart Foundation Grant (TSA BHF 2010/01). Robin Morris receives consultancy fees for P1Vital Limited. The authors disclose no competing interests financial or otherwise.This is the final published version. It first appeared at http://www.biomedcentral.com/content/pdf/s12916-015-0290-y.pdf
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