We propose a formal framework for the description of interactions among groups of neurons. This framework is not restricted to the common case of pair interactions, but also incorporates higher-order ...interactions, which cannot be reduced to lower-order ones. We derive quantitative measures to detect the presence of such interactions in experimental data, by statistical analysis of the frequency distribution of higher-order correlations in multiple neuron spike train data. Our first step is to represent a frequency distribution as a Markov field on the minimal graph it induces. We then show the invariance of this graph with regard to changes of state. Clearly, only linear Markov fields can be adequately represented by graphs. Higher-order interdependencies, which are reflected by the energy expansion of the distribution, require more complex graphical schemes, like constellations or assembly diagrams, which we introduce and discuss. The coefficients of the energy expansion not only point to the interactions among neurons but are also a measure of their strength. We investigate the statistical meaning of detected interactions in an information theoretic sense and propose minimum relative entropy approximations as null hypotheses for significance tests. We demonstrate the various steps of our method in the situation of an empirical frequency distribution on six neurons, extracted from data on simultaneous multineuron recordings from the frontal cortex of a behaving monkey and close with a brief outlook on future work.
We compared--retrospectively--the effects of a 3-month therapy with catechol- O-methyltransferase (COMT) inhibitors tolcapone (100 mg, t.i.d.) and entacapone (200 mg, t.i.d.), on L-DOPA metabolism in ...two groups of parkinsonian patients with motor fluctuations. Plasma and platelets concentrations of L-DOPA and its direct metabolites, dopamine and 3- O-methyldopa (3-OMD), were measured before starting treatment, after two weeks and at the end of treatment. Patients treated with tolcapone showed significant increases in plasma and platelet L-DOPA levels and marked reduction of plasma and platelet 3-OMD levels, both at short- and long-term. Entacapone did not modify L-DOPA levels, while inducing a less marked reduction of plasma and platelet 3-OMD concentrations, with respect to tolcapone, at both time points. Both drugs were similarly effective in increasing plasma and platelet levels of dopamine. These results confirm the different profiles of activity of the two drugs, with tolcapone proving more effective on both the intra- and extra-cellular levels of L-DOPA and 3-OMD.
Superficial adenocarcinoma of the oesophagus is defined as carcinoma limited to the mucosa or submucosa regardless of lymph node status. Columnar epithelium lined lower oesophagus, now generally ...referred to as Barrett's oesophagus, is probably the main cause of adenocarcinoma in the lower oesophagus. Twelve cases of superficial adenocarcinoma arising in Barrett's oesophagus are presented. They were observed over a 6 year period and taken from a series of 50 cases of patients with Barrett's oesophagus and adenocarcinoma, a prevalence of 24%. Endoscopic diagnosis of malignancy was made in six patients. The initial biopsies showed an adenocarcinoma in six patients and some degrees of dysplasia in the other six patients. Prior to surgery, a histological diagnosis of adenocarcinoma was made in all twelve patients. In four patients the adenocarcinoma was confined to the mucosa, and in eight it extended to the submucosa. One patient had a metastatic lymph node. Ten patients are alive without evidence of tumour spread after a mean follow-up of 30 months.
This paper describes the methodology followed for characterizing a commercial CCD camera as a luminance meter for measurements in road light plant. Actually several commercial CCD cameras have been ...proposed on the market for this type of application and they are sold with full working software including a factory calibration in luminance units (cd/m/sup 2/). In fact the availability of a high number of closely spaced small detectors (pixels) on a single chip permits analyses almost impossible or very time consuming if carried out with traditional instrument. These devices are sold at prices lower than scientific grade CCD cameras that usually are not commercialized with a V(/spl lambda/) filter and therefore they could not have a calibration in luminance units. The main counterparts are in the difficulties to define accuracy of measurement, in the low resolution of the A/D converter and in the characteristics of CCD sensor itself. To obtain the best possible results with this type of luminance meters it is necessary to reach a complete metrological characterization and to quantify all the possible effects that could degrade their performances in real measurement situations. In this way the measurement uncertainties might be evaluated correctly and the results could be corrected, if necessary, with ad hoc algorithms.
I clienti delle banche sono, in media, tutt’altro che specialisti della decisione quando sono chiamati a decidere come investire i loro risparmi. II prendere decisioni in ambito finanziario non ...rappresenta per loro una routine. Eppure, le scelte che sono chiamati a fare sortiranno effetti significativi nel tempo e potranno anche essere fonti di serie preoccupazioni. Con il tempo, però, i clienti acquisiscono una certa esperienza e tendono a valutare i potenziali investimenti attraverso la considerazione di caratteristiche specifiche.
Ritanserin, a new serotonin antagonist selective upon S2 receptor subclass is available. Thus, in order to better define the positive control of serotoninergic pathway on proopiomelanocortin ...(POMC)-related peptide release, a group of 7 healthy male volunteers has been submitted to a 5-hydroxytryptophane (5-OH-TP) test (200 mg p.o.) before and after 4 days Ritanserin pretreatment. Plasma beta-endorphin (beta-EP), beta-lipotropin (beta-LPH) and cortisol levels were measured hourly for 4 h after each 5-OH-TP loading. Hormonal levels were measured by specific RIAs on extracted (cortisol) and chromatographed (beta-EP and beta-LPH) plasma samples. Basal plasma concentrations of the three hormones were unchanged by Ritanserin pretreatment. Similarly, the integrated areas of beta-LPH, beta-EP and cortisol release in response to 5-OH-TP remained unaffected by the receptor blockade. These data confirm that serotonin-acting drugs are able to stimulate POMC-related peptide release and indicate that such interaction is not mediated through S2 receptor subclass.
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