Framework for interactive million-neuron simulation.

SUMMARY: Large simulations have become increasingly complex in many fields, tending to incorporate scale-dependent modeling and algorithms and wide-ranging physical influences. This scale of simulation sophistication has not yet been matched in neuroscience. The authors describe a framework aimed at enabling natural interaction with complex simulations: their configuration, initial conditions, monitoring, and analysis. The architecture is built on three cornerstone components: active probes, adaptive data capture, and visual interface. The resulting synthesis will enable interactive exploration of live simulations running on supercomputing platforms.     

No clinical evidence base to support the hygiene hypothesis.

The hygiene hypothesis is a popular explanation for recent increases in allergy in the western world. This hypothesis suggests that development of allergy (or asthma) could be prevented by exposure to immune stimulants such as viruses, bacteria and endotoxins, in particular in the prenatal period or early childhood. How evidence-based are the observations which support the hygiene hypothesis? All clinical epidemiological indications in favour of the hypothesis are based on observational (cross-sectional and cohort) studies and not on observations in randomised controlled intervention studies. In cross-sectional studies no causal relationships can be assessed with sufficient validity. Also in cohort studies there are validity problems, as the exposure is not determined by chance (by means of randomisation) and could be influenced by behaviour. And behaviour might well be a confounder, since it can be associated with both exposure and outcome. A problem is that, without being appropriately tested in well designed prospective research, the hygiene hypothesis has currently already become so popular in the news media that an increased occurrence of asthma might even be induced as a result of an increased exposure. Although the currently available evidence to support the hygiene hypothesis is poor, it appears that the hypothesis has to some become a matter of faith or ideology. Scientists should take care that messages imparted to the general public do not go beyond or conflict with existing evidence.     

The debit balance of present day stress research.

Stress often precedes psychiatric disorders. This holds particularly for the group of mood disorders. A crucial question is whether stress is an epiphenomenon or a decisive factor in the causation of (certain forms of) mood disorder. Certainty about this question can only be obtained when it can be demonstrated that stress phenomena may induce changes in brain functioning similar to the ones supposedly associated with (certain forms of) depression. Since the phenomenology of stress syndromes, as well as their emotional intensity, are highly variable, careful diagnosis is a first requirement. In studies into the significance of stress in the occurrence of depression this degree of finesse has not been achieved. The major shortcomings are discussed. Those should be systematically addressed to provide this type of research with the necessary acuity     

Volumetrical measurements in vestibular schwannoma, the influence of slice thickness and patient's repositioning.

OBJECTIVE: Conservative treatment in vestibular schwannomas is mainly dependent on optimal tumor size determination. The first objective of this study was to establish interobserver and intraobserver variability and the accuracy and reproducibility of three different measurement methods: one bidimensional and two volumetrical. The second objective was to evaluate the influence of the use of different magnetic resonance imaging (MRI) slice thickness and the influence of patient's repositioning on the measurements' outcome. STUDY DESIGN: Two consecutive studies have been prospectively performed, both mainly concerning volumetrical measurements. SETTING: Both studies were performed in a tertiary academic, multidisciplinary center. PATIENTS: In the first study, 19 patients were included between March 1996 and May 2002, with a total of 52 scans. The second study comprised 14 patients. All patients in the first study had at least two MRI examinations performed according to a standard protocol (T1-weighted gadolinium-enhanced, slice thickness of 3 mm, and interslice gap of 0.3 mm). The population in the second study underwent a conservative wait and scan (W&S) treatment. METHODS: Both studies are discussed separately. In the first study, all scans were measured by four investigators, two of whom performed the measurements twice using three different methods. The first method concerns a manually performed bidimensional surface measurement along the petrous pyramid. The second method concerns a semiautomatic volumetrical measurement on a computer, relying on contour detection, and the last method concerns a fully automatic volume reconstruction also performed on a computer using different gray shade scales.All 14 patients included in the second study underwent three magnetic examinations. Three different T1-weighted gadolinium-enhanced sequences were used: the first using a slice thickness of 1 mm, the second again with 1-mm slice thickness but after having repositioned the patient. In the third sequence, a slice thickness of 3 mm was used. All scans were measured by two investigators using the three different methods, as described previously. RESULTS: The manual surface method shows large intraobserver variability, and its reproducibility is significantly lower compared with volume measurements. Because of a relatively large systematic error in small tumors, sensitivity of growth detection is low. Both volumetrical methods are hardly interobserver- and intraobserver-dependent, and the gray shade method turned out to be the most accurate. Radiologic progression is only significant at a volume increase of at least 50%. The influence of patient repositioning is negligible, whereas the use of 1-mm slice thickness seems to be superior to a 3-mm slice thickness. CONCLUSION: The volumetrical gray shade method is the most accurate method to detect early tumor progression. As tumor increase of at least 50% is needed to be able to speak of statistically significant tumor growth, the absence of radiologic progression does not mean that there is no tumor growth. Repositioning of the patient has no influence on the measurements' outcome, whereas for optimal magnetic resonance imaging examinations, a 1-mm slice thickness protocol seems to be superior.     

Mandibular atrophy and metabolic bone loss. Mandibular ridge augmentation by combined sandwich-visor osteotomy and resorption related to metabolic bone state. A 5-year follow-up

92 patients, 31 with and 61 without signs of metabolic bone loss, were treated with a combined sandwich-visor osteotomy. A 5-year follow-up showed a significantly higher rate of resorption in patients with radiographic signs of metabolic bone loss. The analysis was based upon lateral cephalometry.     

Serum prolactins in the diagnosis of epilepsy: sensitivity, specificity, and predictive value

Serum prolactin levels rise after generalized tonic-clonic and partial complex seizures, but not after pseudoepileptic seizures. The criteria for a significant elevation in serum prolactin vary with individual investigators. The prevalence of pseudoseizures in the population studied determines the predictive value of serum prolactin determinations. In populations where most patients have epilepsy, a rise in serum prolactin is highly predictive for true epilepsy, but no increase in serum prolactin is not predictive for pseudoseizures.