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Experience-driven formation of parts-based representations in a model of layered visual memory
(2009)
Growing neuropsychological and neurophysiological evidence suggests that the visual cortex uses parts-based representations to encode, store and retrieve relevant objects. In such a scheme, objects are represented as a set of spatially distributed local features, or parts, arranged in stereotypical fashion. To encode the local appearance and to represent the relations between the constituent parts, there has to be an appropriate memory structure formed by previous experience with visual objects. Here, we propose a model how a hierarchical memory structure supporting efficient storage and rapid recall of parts-based representations can be established by an experience-driven process of self-organization. The process is based on the collaboration of slow bidirectional synaptic plasticity and homeostatic unit activity regulation, both running at the top of fast activity dynamics with winner-take-all character modulated by an oscillatory rhythm. These neural mechanisms lay down the basis for cooperation and competition between the distributed units and their synaptic connections. Choosing human face recognition as a test task, we show that, under the condition of open-ended, unsupervised incremental learning, the system is able to form memory traces for individual faces in a parts-based fashion. On a lower memory layer the synaptic structure is developed to represent local facial features and their interrelations, while the identities of different persons are captured explicitly on a higher layer. An additional property of the resulting representations is the sparseness of both the activity during the recall and the synaptic patterns comprising the memory traces. Keywords: visual memory, self-organization, unsupervised learning, competitive learning, bidirectional plasticity, activity homeostasis, parts-based representation, cortical column
Echocardiography is increasingly used in the management of the critically ill patient as a non-invasive diagnostic and monitoring tool. Whilst in few countries specialized national training schemes for intensive care unit (ICU) echocardiography have been developed, specific guidelines for ICU physicians wishing to incorporate echocardiography into their clinical practice are lacking. Further, existing echocardiography accreditation does not reflect the requirements of the ICU practitioner. The WINFOCUS (World Interactive Network Focused On Critical UltraSound) ECHO-ICU Group drew up a document aimed at providing guidance to individual physicians, trainers and the relevant societies of the requirements for the development of skills in echocardiography in the ICU setting. The document is based on recommendations published by the Royal College of Radiologists, British Society of Echocardiography, European Association of Echocardiography and American Society of Echocardiography, together with international input from established practitioners of ICU echocardiography. The recommendations contained in this document are concerned with theoretical basis of ultrasonography, the practical aspects of building an ICU-based echocardiography service as well as the key components of standard adult TTE and TEE studies to be performed on the ICU. Specific issues regarding echocardiography in different ICU clinical scenarios are then described. Obtaining competence in ICU echocardiography may be achieved in different ways – either through completion of an appropriate fellowship/training scheme, or, where not available, via a staged approach designed to train the practitioner to a level at which they can achieve accreditation. Here, peri-resuscitation focused echocardiography represents the entry level – obtainable through established courses followed by mentored practice. Next, a competence-based modular training programme is proposed: theoretical elements delivered through blended-learning and practical elements acquired in parallel through proctored practice. These all linked with existing national/international echocardiography courses. When completed, it is anticipated that the practitioner will have performed the prerequisite number of studies, and achieved the competency to undertake accreditation (leading to Level 2 competence) via a recognized National or European examination and provide the appropriate required evidence of competency (logbook). Thus, even where appropriate fellowships are not available, with support from the relevant echocardiography bodies, training and subsequently accreditation in ICU echocardiography becomes achievable within the existing framework of current critical care and cardiological practice, and is adaptable to each countrie's needs.
Background: Local adaptation to divergent environmental conditions can promote population genetic differentiation even in the absence of geographic barriers and hence, lead to speciation. Perturbations by catastrophic events, however, can distort such parapatric ecological speciation processes. Here, we asked whether an exceptionally strong flood led to homogenization of gene pools among locally adapted populations of the Atlantic molly (Poecilia mexicana, Poeciliidae) in the Cueva del Azufre system in southern Mexico, where two strong environmental selection factors (darkness within caves and/or presence of toxic H2S in sulfidic springs) drive the diversification of P. mexicana. Nine nuclear microsatellites as well as heritable female life history traits (both as a proxy for quantitative genetics and for trait divergence) were used as markers to compare genetic differentiation, genetic diversity, and especially population mixing (immigration and emigration) before and after the flood. Results: Habitat type (i.e., non-sulfidic surface, sulfidic surface, or sulfidic cave), but not geographic distance was the major predictor of genetic differentiation. Before and after the flood, each habitat type harbored a genetically distinct population. Only a weak signal of individual dislocation among ecologically divergent habitat types was uncovered (with the exception of slightly increased dislocation from the Cueva del Azufre into the sulfidic creek, El Azufre). By contrast, several lines of evidence are indicative of increased flood-induced dislocation within the same habitat type, e.g., between different cave chambers of the Cueva del Azufre. Conclusions: The virtual absence of individual dislocation among ecologically different habitat types indicates strong natural selection against migrants. Thus, our current study exemplifies that ecological speciation in this and other systems, in which extreme environmental factors drive speciation, may be little affected by temporary perturbations, as adaptations to physico-chemical stressors may directly affect the survival probability in divergent habitat types.
Background: Thymostimulin is a thymic peptide fraction with immune-mediated cytotoxicity against hepatocellular carcinoma (HCC) in vitro and palliative efficacy in advanced HCC in two independent phase II trials. The aim of this study was to assess the efficacy of thymostimulin in a phase III trial. Methods: The study was designed as a prospective randomised, placebo-controlled, double-blind, multicenter clinical phase III trial. Between 10/2002 and 03/2005, 135 patients with locally advanced or metastasised HCC (Karnofsky [greater than or equal to]60% / Child-Pugh [less than or equal to]12) were randomised to receive thymostimulin 75 mg s.c. 5x/week or placebo stratified according to liver function. Primary endpoint was twelve-month survival, secondary endpoints overall survival (OS), time to progression (TTP), tumor response, safety and quality of life. A subgroup analysis according to liver function, KPS and tumor stage (Okuda, CLIP and BCLC) formed part of the protocol. Current Controlled Trials ISRCTN64487365. Results: Twelve-month survival was 28% [95%CI 17-41; treatment] and 32% [95%CI 19-44; control] with no significant differences in median OS (5.0 [95% CI 3.7-6.3] vs. 5.2 [95% CI 3.5-6.9] months; p=0.87, HR=1.04 [95% CI 0.7-1.6]) or TTP (5.3 [95%CI 2.0-8.6] vs. 2.9 [95%CI 2.6-3.1] months; p=0.60, HR=1.13 [95% CI 0.7-1.8]). Adjustment for liver function, Karnofsky status or tumor stage did not affect results. While quality of life was similar in both groups, fewer patients on thymostimulin suffered from accumulating ascites and renal failure. Conclusions: In our phase III trial, we found no evidence of any benefit to thymostimulin in the treatment of advanced HCC and there is therefore no justification for its use as single-agent treatment. The effect of thymostimulin on hepato-renal function requires further confirmation. trial registration: Current Controlled Trials ISRCTN64487365
Background: Reactive oxygen species (ROS) and reactive nitrogen species (RNS) are produced during hemorrhagic shock and resuscitation (H/R), which may contribute to multiple organ failure. The AIM of this study was to test the hypothesis that green tea (Camellia sinenesis) extract containing 85% polyphenols decreases injury after H/R in rats by scavenging ROS and RNS. Method: S: Female Sprague Dawley rats were given 100 mg polyphenol extract/kg body weight or vehicle 2 h prior to hemorrhagic shock. H/R was induced by two protocols: 1) withdrawal of blood to a mean arterial pressure of 40 mm Hg followed by further withdrawals to decrease blood pressure progressively to 28 mm Hg over 1 h (severe), and 2) withdrawal of blood to a sustained hypotension of 40 mm Hg for 1 h (moderate). Rats were then resuscitated over 1 h with 60% of the shed blood volume plus twice the shed blood volume of lactated Ringer's solution. Serum samples were collected at 10 min and 2 h after resuscitation. At 2 or 18 h, livers were harvested for cytokine and 3-nitrotyrosine quantification, immunohistochemical detection of 4-hydroxynonenol (4-HNE) and inducible nitric oxide synthase (iNOS) protein expression. Results: After severe H/R, 18-h survival increased from 20% after vehicle to 70% after polyphenols (p<0.05). After moderate H/R, survival was greater (80%) and not different between vehicle and polyphenols. In moderate H/R, serum alanine aminotransferase (ALT) increased at 10 min and 2 h postresuscitation to 345 and 545 IU/L, respectively. Polyphenol treatment blunted this increase to 153 and 252 IU/L at 10 min and 2 h (p<0.01). Polyphenols also blunted increases in liver homogenates of TNFalpha (7.0 pg/mg with vehicle vs. 4.9 pg/mg with polyphenols, p<0.05), IL-1beta (0.80 vs. 0.37 pg/mg, p<0.05), IL-6 (6.9 vs. 5.1 pg/mg, p<0.05) and nitrotyrosine (1.9 pg/mg vs. 0.6 pg/mg, p<0.05) measured 18 h after H/R. Hepatic 4-HNE immunostaining indicative of lipid peroxidation also decreased from 4.8% after vehicle to 1.5% after polyphenols (p<0.05). By contrast, polyphenols did not block increased iNOS expression at 2 h after H/R. CONCLUSION: Polyphenols decrease ROS/RNS formation and are beneficial after hemorrhagic shock and resuscitation.
Background: Because Endomyocardial Biopsy has low sensitivity of about 20%, it can be performed near to myocardium that presented as Late Gadolinium Enhancement (LGE) in cardiovascular magnetic resonance (CMR). However the important issue of comparing topography of CMR and histological findings has not yet been investigated. Thus the current study was performed using an animal model of myocarditis. Results: In 10 male Lewis rats Experimental Autoimmune myocarditis was induced, 10 rats served as control. On day 21 animals were examined by CMR to compare topographic distribution of LGE to histological inflammation. Sensitivity, specificity, positive and negative predictive values for LGE in diagnosing myocarditis were determined for each segment of myocardium. Latter diagnostic values varied widely depending on topographic distribution of LGE and inflammation as well as on the used CMR sequence. Sensitivity of LGE was up to 76% (left lateral myocardium) and positive predictive values were up to 85% (left lateral myocardium), whereas sensitivity and positive predictive value dropped to 0 - 33% (left inferior myocardium). Conclusions: Topographic distribution of LGE and histological inflammation seem to influence sensitivity, specifity, positive and negative predictive values. Nevertheless, positive predictive value for LGE of up to 85% indicates that Endomyocardial Biopsy should be performed "MR-guided". LGE seems to have greater sensitivity than Endomyocardial Biopsy for the diagnosis of myocarditis.
Im vorliegenden Arbeitspapier werden alternative normative Grundpositionen der Familienpolitik diskutiert und die Entwicklung der relativen Verteilungspositionen von Haushalten unterschiedlicher Größe bzw. von Familien mit und ohne Kinder untersucht. Die empirische Analyse stützt sich zum einen auf veröffentlichte Tabellen des Statistischen Bundesamtes und zum anderen auf eigene Auswertungen der Einkommens- und Verbrauchsstichproben 1973, 1978 und 1983 sowie des Sozio-ökonomischen Panels für einzelne Stichjahre der späteren Periode und insbesondere für die Ausgangssituation und die bisherigen Veränderungen in den neuen Bundesländern. Als Indikator für die Einkommenslage von Personen wird ein Äquivalenzeinkommen in Relation zum jeweiligen Gruppen- oder Gesamtdurchschnitt, die sogenannte Wohlstandsposition, herangezogen. Personen in Haushalten mit drei oder mehr Personen - das sind hauptsächlich Familien mit Kindern - schneiden erwartungsgemäß im Durchschnitt schlechter ab als Personen in kleineren Haushalten. Allerdings sind die Diskrepanzen innerhalb der Gruppen, die überwiegend von Transfers leben, mäßiger als innerhalb der Gruppen mit erwerbstätigem Haushaltsvorstand; anscheinend wirkt der Familienlastenausgleich in den sozial schwächeren Gruppen stärker. Zwischen 1972 und 1992 (Westdeutschland) hat sich die relative Position der größeren Haushalte allerdings tendenziell etwas verschlechtert. Die Verteilungsanalyse auf der Basis der erwähnten Mikrodaten zeigt zudem, daß Familien mit Kindern wesentlich häufiger unterhalb der durchschnittlichen Wohlstandsposition und unterhalb der relativen Armutslinie von 50 % einzuordnen sind als (Ehe-)Paare ohne Kinder. Besonders ungünstig sieht die Situation bei den Alleinerziehenden aus; die Armutsquote dieser Gruppe schwankt zwischen einem Fünftel und einem Viertel. In der ehemaligen DDR scheint die relative Position der Familien mit Kindern überwiegend besser gewesen zu sein; die Strukturen in den neuen Bundesländern haben sich aber bereits denen in Westdeutschland angenähert.
Dieser Beitrag vergleicht mit einheitlicher Methodik die Mobilität des individuellen Bruttoarbeitseinkommens, des Bruttoäquivalenzeinkommens und des Nettoäquivalenzeinkommens in Westdeutschland, Ostdeutschland, Großbritannien, den USA und Ungarn mit Panel-Daten dieser Länder aus dem Zeitraum 1989-1995. Die Mobilität ist in Ostdeutschland bei allen Einkommenskonzepten wesentlich höher als in Westdeutschland, nähert sich aber im Zeitablauf und insbesondere beim Nettoäquivalenzeinkommen dem westdeutschen Niveau an. Die Mobilität des Bruttoäquivalenzeinkommens ist in Westdeutschland größer, die des Nettoäquivalenzeinkommens kleiner als in Großbritannien. Die Mobilität des individuellen Bruttoarbeitseinkommens und des Bruttoäquivalenzeinkommens ist in Westdeutschland höher, die des Nettoäquivalenzeinkommens niedriger als in den USA. Die Mobilität des Nettoäquivalenzeinkommens ist in Ungarn deutlich höher als in Ostdeutschland. Diese Ergebnisse zeigen eine im internationalen Vergleich unerwartet hohe Flexibilität des deutschen Arbeitsmarkts, wobei jedoch die Verweildauer in der Arbeitslosigkeit in Deutschland länger ist als in den USA und Großbritannien, wo viele Arbeitslose schnell in schlecht bezahlte Jobs wechseln. Ferner zeigt sich, daß das Steuer- und Transfersystem in keiner anderen Volkswirtschaft die Mobilität der Bruttoäquivalenzeinkommen stärker reduziert als in Deutschland.
This paper aims to provide a descriptive analysis of the changing patterns of labour market participation, non-participation and unemployment in Great Britain, Sweden and Germany. Since the mid 1970s, most European countries have experienced two parallel developments: on the one hand they have witnessed a huge growth in the proportion of women participating on the labour market. On the other however, they have experienced the return of mass unemployment and a growing insecurity of employment for those in work. In this paper, a typology of work histories is constructed using decade periods. Retrospective and panel data from Germany, Britain and Sweden are then used to compare the effects of different employment and welfare regimes on the proportions of respondents with different types of work histories and how these are combined with unemployment.