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  • 1
    ISSN: 1432-1106
    Keywords: MEG ; MRI ; Localization methods ; P100-P200 ; Human
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary The purpose of this study was to compare the relative efficacy of two methods in assessing the location of the sources of the N100 and P200 components of evoked magnetic fields (EMFs) to transient tone stimuli. EMFs to left ear stimulation, containing both components, were recorded over the right hemisphere of six normal subjects. The magnetic scalp distributions calculated at several adjacent time points, covering the duration of each component's peak, were used to estimate the source parameters of each component. Good estimates of the source of both components were obtained from all magnetic field distributions. The averaged spatial parameters derived from all distributions of each component as well as the parameters derived from the distribution that gave the best source estimate for each component were projected onto magnetic resonance images of subject's head. It was found that the source of each component is located on the superior surface of the temporal lobe and that the source of the P200 component is anterior to the N100 source in all subjects using both procedures.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1432-1041
    Keywords: Insulin ; Fosinopril ; insulin sensitivity ; glucose tolerance ; lipoproteins ; ACE inhibition ; normal humans ; blood pressure ; adverse effects
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Medicine
    Notes: Summary The effect of the new ACE-inhibitor, fosinopril, on insulin sensitivity (SI), glucose homoeostasis and lipid profile has been examined in 24 young, healthy, normotensive men. SI, fasting plasma glucose and insulin, serum total triglycerides (Tg) and lipoprotein cholesterol (C) fractions, and ACE activity were assessed after subjects had taken placebo for 1 week and after 3 further weeks either on placebo (12 subjects) or fosinopril 20 mg daily (12 subjects), administered in a doubleblind, randomized order. Measurements were made after 3 days on a standard diet (2500 kcal/d, 45% carbohydrates, 40% fat and 15% proteins) and after an over-night fast. Compared with control values at the end of the runin placebo phase, fosinopril reduced plasma ACE activity (from 106 to 24 nmol·ml−1·min−1), Significantly increased plasma potassium and lowered upright systolic blood pressure. It also improved the k-value of the glucose disappearance rate after glucose load (from −1.70 to −1.88%·min−1) and tended to increase SI slightly although not significantly (from 10.2 to 12.0·10−4·min−1·μU−1·ml−1). Fasting plasma glucose, insulin, serum total, high-, low-, and very-low density lipoprotein cholesterol fractions and total triglycerides were unchanged following fosinopril and placebo. The findings indicate that in healthy lean humans, ACE inhibition with fosinopril is neutral with regard to lipoprotein and carbohydrate metabolism, and that it may slightly enhance cellular glucose disposal. This calls for further evaluation in individuals at high risk of developing insulin resistance and in patients with impaired insulin sensitivity related to hypertension, obesity, decreased glucose tolerance and diabetes mellitus.
    Type of Medium: Electronic Resource
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  • 3
    ISSN: 1573-6792
    Keywords: Auditory responses ; Magnetoencephalography ; Single current dipole ; Distributed current ; Magnetic Field Tomography (MFT)
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary Measurements of the magnetic field elicited by a 50 ms long auditory stimulus, from three normal subjects and one head injured subject, are used to estimate the three dimensional distribution of generators in the brain. The resulting images are compared with point source solutions obtained with the usual single current dipole fitting procedures, over a latency range which includes the extrema in the (average) measured signal. In all cases considered, 100 or so epochs time-locked to the stimulus were magnetically recorded. These were averaged, and then analyzed using two techniques; a new distributed current model known as Magnetic Field Tomography (MFT), and the standard single current dipole (SCD) model. Both methods provide estimates of the current generators in the brain. In two of the normal subjects, the MFT solutions are super-imposed onto Magnetic Resonance Images (MRI) of the relevant cortical area. The results show that when the SCD model provides a reasonable description of the data, the MFT estimate shows one dominant localized region in agreement with the current dipole position. In the MFT sequence of solutions the activity evolves smoothly; multiple areas of activity often arise as the focal activity in one region declines while focal activity in another region grows. In contrast the SCD solutions during these intermediate periods fit the data poorly, and may move erratically from one locale to another. We conclude that MFT seems to provide a reasonable description of the activity through cortical and subcortical regions. The evolution of activity, as derived from the average signal, can be traced continuously from the onset of the stimulus, not just at the peaks. This could be particularly important for clinical applications where injury or other pathology produce a response with no clear dipolar pattern.
    Type of Medium: Electronic Resource
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