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M Brammer

Publications and source records attributed to M Brammer.

At least 55 records · Page 3Linked to original sources
PubMed1995

Against the laterality index as a measure of cerebral asymmetry.

The laterality index (right - left)/(right + left) has been widely used to measure cerebral asymmetry. However, its validity rests on the assumption that confounding effects of overall head and body size are symmetrical on both sides of the brain. We have found that this assumption may not always be justified. In magnetic resonance imaging data from a group of 43 right-handed normal control and schizophrenic subjects, the laterality index controlled poorly for the asymmetrical confounding effect of height, leading to a spurious (although statistically significant) correlation between height and apparent cerebral asymmetry. Regression modeling is advocated as a more rational and effective way to explore and control size effects confounding cerebral lateralization.

Adult↗
PubMed1995

Computerized brain tissue classification of magnetic resonance images: a new approach to the problem of partial volume artifact.

Due to the finite spatial resolution of digital magnetic resonance images of the brain, and the complexity of anatomical interfaces between brain regions of different tissue type, it is inevitable that some voxels will represent a mixture of two or three different tissue types. Outright assignment of such "bipartial" or "tripartial" voxels to one class or another is more problematic and less reliable than assignment of "full-volume" voxels, wholly representative of a single tissue type. We have developed a computerized system for brain tissue classification of dual echo MR data, which uses a polychotomous logistic model for discriminant analysis, combined with a Bayes allocation rule incorporating differential prior probabilities, and spatial connectivity tests, to assign each voxel in the image to one of four possible classes: gray matter, white matter, cerebrospinal fluid, or unclassified. The system supports automated volumetric analysis of segmented images, has low operational overheads, and compares favorably with previous multivariate or "multispectral" approaches to brain MR image segmentation in terms of both validity (bootstrap misclassification rate = 3.3%) and interoperator reliability (intra-class correlation coefficients for all three tissue classes > 0.9). We argue that these improvements in performance stem from better methodological management of the related problems of non-Normality of MR signal intensity values and partial volume artifact.

Artifacts↗
PubMed1995

Activation of area V5 by visual perception of motion demonstrated with echoplanar MR imaging.

Cortical activation in visual association areas known to be responsible for the perception of motion was investigated in two volunteers who viewed a projected animated cartoon periodically "run" and "frozen" during collection of echoplanar MR images. Ten axial, contiguous, 5 mm thick, T2-weighted, gradient-echo images (TE 40 ms, TR 3000 ms) depicting BOLD contrast were acquired through the occipital lobe using a GE Signa 1.5 T system with an advanced NMR operating console. Images were analysed by time series regression modelling estimating power in the MR signal at the ON-OFF frequency of motion. Highly significant activation in response to motion perception was identified in both subjects bilaterally in area V5.

Echo-Planar Imaging↗
PubMed1995

Cerebral hemispheric asymmetry revisited: effects of handedness, gender and schizophrenia measured by radius of gyration in magnetic resonance images.

Abnormal patterns of cerebral hemispheric asymmetry have been inconsistently reported in association with schizophrenia. Radius of gyration (Rg) is a measure of the mean dispersion of points in a radially organized structure about that structure's centre of gravity. We developed computerized methods for estimating Rg of the magnetic resonance image (MRI) boundary between cortex and subcortex, and applied these methods to measurement of cerebral hemispheric asymmetry in 37 schizophrenics (SZs) and 30 controls (CONs). In right-handed CONs, Rg of right brain boundaries was significantly greater than Rg of left brain boundaries; in left-handed CONs, Rg of left brain boundaries was significantly greater than Rg of right brain boundaries. In right-handed males (both SZ and CON) there were significant differences in Rg between hemispheres; whereas in females (both SZ and CON), there were no such differences. Right-handed male SZs (N = 26) were distinguished by reversal of the right-handed male CON pattern of interhemispheric difference in Rg, and by global reduction in Rg of right brain boundaries. These was no evidence for significant abnormality of Rg in right-handed female SZs (N = 7). There findings suggest an important interactive effect of gender and schizophrenia on lateralized cerebral structure.

Adult↗
PubMed1994

Inhibition of K+ channel activity by 4-AP stimulates N-type Ca2+ channels in CHP-100 cells.

The potassium channel blocker, 4-aminopyridine (4-AP), stimulates neurotransmitter release via plasma membrane depolarization and subsequent activation of voltage-gated calcium channels. The present study assessed the effects of 4-AP on intracellular calcium levels in the human neuroblastoma cell line CHP-100. Blockade of K+ channels with 4-AP significantly increased intracellular calcium concentration ([Ca2+]i). This increase occurred via activation of plasma membrane Ca2+ channels. The 4-AP induced rise in [Ca2+]i was not inhibited by the L-type Ca2+ channel blocker nifedipine but was sensitive to the N-type Ca2+ channel blocker omega-contotoxin GVIA. Tetrodotoxin did not alter the effect of 4-AP. These results suggest that in CHP-100 cells, following inhibition of K+ channels by 4-AP, N-type Ca2+ channels are activated.

4-Aminopyridine↗
PubMed1994

Fractal analysis of the boundary between white matter and cerebral cortex in magnetic resonance images: a controlled study of schizophrenic and manic-depressive patients.

This paper reports development of a computerized ('box-counting') method for estimation of fractal dimension (FD) of the magnetic resonance image (MRI) boundary between cerebral cortex and white matter; and the application of this method to MRIs of 39 schizophrenics (SZs), 23 manic-depressives (MDs) and 31 controls (CONs). Mean FD across all diagnostic groups was 1.402; 95% confidence interval (CI) 1.399 to 1.406. Mean FD was greater in boundaries extracted from manic-depressive patients than in boundaries extracted from controls (difference between MD and CON mean FDs = 0.008; 95% CI -0.002 to +0.018); and less in schizophrenics than in controls (difference between SZ and CON mean FDs = -0.003; 95% CI -0.011 to +0.005). Mean FD was positively correlated with subcortical volume and anterior cerebral volume, and negatively correlated with sulcal cerebrospinal fluid volume. Significant differences in mean FD between diagnostic groups were demonstrated by analysis of covariance (ANCOVA; P < 0.01), with age and volumetric measures of brain size as covariates; and manic-depressive boundaries were shown to have significantly greater values for residual FD (after controlling for effects of brain size) than boundaries extracted from controls (t test; P < 0.05). It is proposed that FD is a useful measure of clinically relevant differences in the complexity of MRI boundaries.

Adult↗
PubMed1992

A new technique for fractal analysis applied to human, intracerebrally recorded, ictal electroencephalographic signals.

Application of a new method of fractal analysis to human, intracerebrally recorded, ictal electroencephalographic (EEG) signals is reported. 'Frameshift-Richardson' (FR) analysis involves estimation of fractal dimension (1 < FD < 2) of consecutive, overlapping 10-s epochs of digitised EEG data; it is suggested that this technique offers significant operational advantages over use of algorithms for FD estimation requiring preliminary reconstruction of EEG data in phase space. FR analysis was found to reduce substantially the volume of EEG data, without loss of diagnostically important information concerning onset, propagation and evolution of ictal EEG discharges. Arrhythmic EEG events were correlated with relatively increased FD; rhythmic EEG events with relatively decreased FD. It is proposed that development of this method may lead to: (i) enhanced definition and localisation of initial ictal changes in the EEG presumed due to multi-unit activity; and (ii) synoptic visualisation of long periods of EEG data.

Algorithms↗
PubMed1992

Prognosis in glomerulonephritis. III. A longitudinal analysis of changes in serum creatinine and proteinuria during the course of disease: effect of immunosuppressive treatment. Report from Copenhagen Study Group of Renal Diseases.

A total of 395 consecutive patients with biopsy-proven glomerulonephritis were followed up for 14 years. At the time of entry to the study the patients were classified as having one of nine states of kidney disease according to serum creatinine levels and proteinuria. The transitions of the patients between the nine states were analysed. The influence of 14 independent variables including treatment with cytostatic drugs and prednisolone was estimated by the Cox proportional hazard model. Treatment with immunosuppressive drugs had an influence that emerged within the first month and continued for the next 2 months. Subsequent treatment with cytostatic drugs in combination with prednisolone delayed further improvement. Treatment with prednisolone or cytostatic drugs as single therapy for up to 6 months increased the risk of improvement of the disease, and had no significant effect on deterioration. The beneficial effect of the treatment persisted after withdrawal of the immunosuppressive drugs. The analysis revealed only a slight influence of the histological character of the glomerular changes. Post-streptococcal glomerulonephritis carried an increased tendency for improvement. Arterial hypertension affected the process in several states of kidney disease. Heavy proteinuria increased the risk of increasing serum creatinine levels.

Azathioprine↗
PubMed1991

[Cystic space occupying lesion of the upper pole of the kidney in a newborn infant. Case report and differential diagnosis].

In a newborn female infant a cystic lesion in the upper pole of the right kidney was detected by sonography 4 weeks before an uneventful delivery. In the postnatal period the sonographic examination, IVP, CT, and the biochemical data as well were not able to classify definitely this lesion as a benign cyst, adrenal hemorrhage or cystic malignoma. Therefore a laparatomy was performed, which revealed a cystic neuroblastoma.

Diagnosis, Differential↗
PubMed1990

Brain membrane fluidity and lipid peroxidation in Alzheimer's disease.

Membrane fluidity and lipid peroxidation in 4 brain areas from patients with Alzheimer's disease (AD) and matched controls were determined by measuring fluorescence anisotropy of the lipophilic probe 1,6-diphenyl-1,3,5-hexatriene (DPH) and by the thiobarbituric acid test respectively. Fluorescence anisotropy of DPH was not changed in any of the 4 areas in AD compared to controls. Basal levels of malondialdehyde (MDA; an intermediate in the lipid peroxidation process) were also not changed in different brain regions of AD and controls. However, stimulated MDA production determined by incubating tissue with FeSO4 plus H2O2 produced significantly higher MDA levels in AD brain than in controls.

Aged↗
PubMed1989

Kinetic analysis of A23187-mediated polyphosphoinositide breakdown in rat cortical synaptosomes suggests that inositol bisphosphate does not arise primarily by degradation of inositol trisphosphate.

The kinetics of polyphosphoinositide breakdown and inositol phosphate formation have been studied in rat cortical synaptosomes labelled in vitro with myo-[2-3H]inositol. Intrasynaptosomal Ca2+ concentrations have been varied by the use of Ca-EGTA buffers or by adding the ionophore A23187 in the presence and absence of 1 mM Ca2+. The former studies have revealed that, at very low (20 nM) intrasynaptosomal free Ca2+ levels, inositol bisphosphate, but not inositol monophosphate levels are reduced. Addition of A23187 in the absence of added Ca2+ gives rise to greatly enhanced inositol bisphosphate accumulation, which is further enhanced if 1 mM Ca2+ is present in the extrasynaptosomal medium. At all time points examined (down to 2 s after adding ionophore), the ratio of inositol trisphosphate/inositol bisphosphate accumulation does not exceed 0.2, and calculations based on inositol bis- and trisphosphate breakdown rates in synaptosomal lysates suggest that only a minority of the inositol bisphosphate arises from degradation of inositol trisphosphate. Addition of ionophore in the presence (but not in the absence) of 1 mM Ca2+ leads to rapid breakdown of phosphatidylinositol 4,5-bisphosphate (PtdInsP2) and ATP and slower breakdown of phosphatidylinositol 4-phosphate (PtdInsP). The rates of loss of PtdinsP2 and ATP are very highly correlated, suggesting that polyphosphoinositide resynthesis may be limited by ATP availability at high Ca2+ levels. Analysis of 32P-labelled synaptosomes also reveals that A23187 produces Ca2+-dependent losses of PtdInsP2, PtdInsP, ATP, and GTP radioactivity and a marked increase in the radioactivity of a compound distinct from nucleotides or any of the lipid breakdown products tested.(ABSTRACT TRUNCATED AT 250 WORDS)

Adenosine Triphosphate↗
PubMed1988

Cytostatic treatment of glomerular diseases. V. Treatment of glomerulonephritis with cyclophosphamide plus prednisone, azathioprine plus prednisone and cyclophosphamide as monotherapy. A comparative study. A report from a Copenhagen Study Group of Renal Diseases.

Thirty-two patients suffering from biopsy-proven glomerulonephritis with proteinuria greater than or equal to 1.2 g/24 hours and/or creatinine clearance less than 50% of normal value were treated for 6 weeks with prednisone plus cyclophosphamide (C+P), azathioprine (A+P) or cyclophosphamide as a monotherapy (C). The effect of the treatment was evaluated after 6 and 16 weeks. The results were entered consecutively in a sequential analysis. The three treatment regimes were compared mutually as well as with the results of 16 weeks' treatment with C and placebo, published previously. Six weeks' treatment with C+P or A+P was superior to C and at least as efficient as 16 weeks' C treatment. C treatment for 6 weeks was less efficient than 16 weeks' C treatment. The side-effects of the 6 weeks' A+P or C+P treatment were fewer and less serious than those reported from the long-term C treatment.

Adult↗