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PubMed2004

Optical detection of convergent projections in the embryonic chick NTS.

Multiple-site optical recording of neural activity was performed in the nucleus of the tractus solitarius (NTS) of the chick embryo with stimulation of the glossopharyngeal nerve (N. IX) and vagus nerve (N. X). We measured the amplitudes of the optical signals related to glutamate-mediated excitatory postsynaptic responses, and calculated the ratio of the signal evoked by simultaneous N. IX/N. X stimulation to the signal obtained after mathematical summation of the individual N. IX and N. X responses. The ratio was significantly lower than 100% in the rostral region of the NTS, in which postsynaptic responses were elicited by both N. IX and N. X stimulations. This result means that there is a convergence of visceral inputs via the N. IX and N. X in the embryonic chick NTS. The existence of the convergence suggests that the NTS performs complex integration of information from multiple sensory inputs from the early stages of embryogenesis.

Animals↗
PubMed2004

A recurrent neural network with exponential convergence for solving convex quadratic program and related linear piecewise equations.

This paper presents a recurrent neural network for solving strict convex quadratic programming problems and related linear piecewise equations. Compared with the existing neural networks for quadratic program, the proposed neural network has a one-layer structure with a low model complexity. Moreover, the proposed neural network is shown to have a finite-time convergence and exponential convergence. Illustrative examples further show the good performance of the proposed neural network in real-time applications.

Artificial Intelligence↗
PubMed2005

On the global output convergence of a class of recurrent neural networks with time-varying inputs.

This paper studies the global output convergence of a class of recurrent neural networks with globally Lipschitz continuous and monotone nondecreasing activation functions and locally Lipschitz continuous time-varying inputs. We establish two sufficient conditions for global output convergence of this class of neural networks. Symmetry in the connection weight matrix is not required in the present results which extend the existing ones.

Algorithms↗
PubMed2005

Data-partitioning using the Hilbert space filling curves: effect on the speed of convergence of Fuzzy ARTMAP for large database problems.

The Fuzzy ARTMAP algorithm has been proven to be one of the premier neural network architectures for classification problems. One of the properties of Fuzzy ARTMAP, which can be both an asset and a liability, is its capacity to produce new nodes (templates) on demand to represent classification categories. This property allows Fuzzy ARTMAP to automatically adapt to the database without having to a priori specify its network size. On the other hand, it has the undesirable side effect that large databases might produce a large network size (node proliferation) that can dramatically slow down the training speed of the algorithm. To address the slow convergence speed of Fuzzy ARTMAP for large database problems, we propose the use of space-filling curves, specifically the Hilbert space-filling curves (HSFC). Hilbert space-filling curves allow us to divide the problem into smaller sub-problems, each focusing on a smaller than the original dataset. For learning each partition of data, a different Fuzzy ARTMAP network is used. Through this divide-and-conquer approach we are avoiding the node proliferation problem, and consequently we speedup Fuzzy ARTMAP's training. Results have been produced for a two-class, 16-dimensional Gaussian data, and on the Forest database, available at the UCI repository. Our results indicate that the Hilbert space-filling curve approach reduces the time that it takes to train Fuzzy ARTMAP without affecting the generalization performance attained by Fuzzy ARTMAP trained on the original large dataset. Given that the resulting smaller datasets that the HSFC approach produces can independently be learned by different Fuzzy ARTMAP networks, we have also implemented and tested a parallel implementation of this approach on a Beowulf cluster of workstations that further speeds up Fuzzy ARTMAP's convergence to a solution for large database problems.

Algorithms↗
PubMed2007

Semaphorin-1a controls receptor neuron-specific axonal convergence in the primary olfactory center of Drosophila.

In the olfactory system of Drosophila, 50 functional classes of sensory receptor neurons (ORNs) project in a highly organized fashion into the CNS, where they sort out from one another and converge into distinct synaptic glomeruli. We identified the transmembrane molecule Semaphorin-1a (Sema-1a) as an essential component to ensure glomerulus-specific axon segregation. Removal of sema-1a in ORNs does not affect the pathfinding toward their target area but disrupts local axonal convergence into a single glomerulus, resulting in two distinct targeting phenotypes: axons either intermingle with adjacent ORN classes or segregate according to their odorant receptor identity into ectopic sites. Differential Sema-1a expression can be detected among neighboring glomeruli, and mosaic analyses show that sema-1a functions nonautonomously in ORN axon sorting. These findings provide insights into the mechanism by which afferent interactions lead to synaptic specificity in the olfactory system.

Animals↗
PubMed2004

Cortical convergence from different frequency domains in the cat primary auditory cortex.

Primary auditory cortex (AI) has a tonotopic map consisting of orderly isofrequency (IF) bands, and cortical connections are commonly supposed to link domains preferring similar characteristic frequencies (CFs) within AI and in auditory association cortex. The interaction of different frequency channels, however, has not fully been understood in terms of anatomical substrates. Here, by injecting two anterograde tracers in different frequency domains of cat AI, without overlap of the injection cores, we attempted to relate the anatomical mapping of cortical outputs to physiologically defined fields in the auditory cortex. Consistent with previous studies, patches of labeled axon terminals were oriented largely along the IF axis. In regions distant from the injection sites, however, terminal patches were divergent in distribution. This divergence resulted in a complex geometry of partial overlap of projections originating from the two injection sites. The relative extent of the overlap tended to vary depending on the distance between the two injection sites. Physiological mapping for tonotopy across auditory fields revealed that projectional overlap was characteristic of dorsal AI and the dorsoposterior field and, to a lesser extent, in the secondary auditory field. Considering the differences in frequency representation in different AI IF bands, the anatomical convergence of projections tuned to different CFs could contribute to the spectral integration of sound components. Furthermore, the different extent of convergence in the functionally distinct fields might reflect field-specific processing of acoustic signals.

Animals↗
PubMed2005

Coincident stimulation of convergent cortical inputs enhances immediate early gene induction in the striatum.

The effect of coincident stimulation of convergent corticostriatal inputs was analyzed by the induction of immediate early genes in striatal neurons. Cortical motor areas were stimulated through implanted electrodes in awake, behaving rats, and the induction of the mRNAs encoding the immediate early genes (IEGs) c-fos and arc was analyzed in the striatum with in situ hybridization histochemistry. In the first experiment, unilateral stimulation of the medial agranular cortex, orofacial region of the lateral agranular cortex or the forelimb region of the lateral agranular cortex resulted in IEG induction in the striatum, which was restricted to the topographically related area receiving input from the stimulated cortical area. In a second experiment, stimulation parameters were altered, including frequency, number of pulses/train, and number of trains/s. These parameters did not have a significant effect on IEG induction. Notably, in some cases, in which there was IEG induction not only in the stimulated cortical region, but also in the homologous area in the contralateral hemisphere, very robust IEG induction was observed in the striatum. In a third experiment, the orofacial regions of the lateral agranular cortex of both hemispheres were stimulated coincidently. All of these animals showed robust striatal IEG induction. This IEG induction was attenuated by pretreatment with an NMDA antagonist MK-801. In a fourth experiment, we tested whether the coincidence of bilateral cortical stimulation contributed to the efficacy of striatal IEG induction. Either alternating stimulation or coincident stimulation of non-homologous cortical regions produced significantly lower striatal IEG induction than obtained with coincident stimulation of homologous cortical areas. Enhanced striatal IEG induction occurred in indirect striatal neurons, labeled with enkephalin, but was also present in a large number of enkephalin-negative neurons, most of which are likely direct pathway neurons. These results suggest that regional and temporal convergence of cortical inputs enhances striatal IEG induction.

AIDS-Related Complex↗
PubMed2005

Convergence of auditory-nerve fiber projections onto globular bushy cells.

Globular bushy cells are a key element of brainstem circuits that mediate the early stages of sound localization. Many of their physiological properties have been attributed to convergence of inputs from the auditory nerve, many of which are large with complex geometry, but the number of these terminals contacting individual cells has not been measured directly. Herein we report, using cats as the experimental model, that this number ranged greatly (9-69) across a population of 12 cells, but over one-half of the cells (seven of 12) received between 15 and 23 inputs. In addition, we provide the first measurements of cell body surface area, which also varies considerably within this population and is uncorrelated with convergence. For one cell, we were able to document axonal structure over a distance greater than 100 microm, between the soma and the location where the axon expanded to its characteristic large diameter. These data were combined with accumulated physiological information on vesicle release, receptor kinetics and voltage-gated ionic conductances, and incorporated into computational models for four cells that are representative of the structural variation within our sample population. This predictive model reveals that basic physiological features, such as precise first spike latencies and peristimulus time histogram shapes, including primary-like with notch and onset-L, can be generated in these cells without including inhibitory inputs. However, phase-locking is not significantly enhanced over auditory-nerve fibers. These combined anatomical and computational approaches reveal additional parameters, such as active zone density, nerve terminal size, numbers and sources of inhibitory inputs and their activity patterns, that must be determined and incorporated into next-generation models to understand the physiology of globular bushy cells.

Action Potentials↗
PubMed2005

Symmetry breaking and convergent extension in early chordate development.

The initiation of axis, polarity, cell differentiation, and gastrulation in the very early chordate development is due to the breaking of radial symmetry. It is believed that this occurs by an external signal. We suggest instead spontaneous symmetry breaking through the agency of the Turing-Child field. Increased size or decreased diffusivity, both brought about by mitotic activity, cause the spontaneous loss of stability of the homogeneous state and the evolution of the metabolic pattern during development. The polar metabolic pattern is the cause of polar gene expression, polar morphogenesis (gastrulation), and polar mitotic activity. The Turing-Child theory explains not only the spontaneous formation of the invagination in gastrulation but also the coherent cell movement observed in convergence and extension during gastrulation and neurulation. The theory is demonstrated with respect to experimental observations on the early development of fish, amphibian, and the chick. The theory can explain a multitude of experimental details. For example, it explains the splayed polar progression of reduction in the fish blastoderm. Reduction starts on that side of the blastoderm margin, which will initiate invagination several hours later. It progresses toward the blastoderm center and somewhat laterally from this future "dorsal lip". This is precisely as predicted by a Turing-Child system in a circle. And for a fish like zebrafish with a blastoderm that is slightly oval, reduction is observed to progress along the long axis of the ellipse, which is what Turing-Child theory predicts. In general the shape and the chemical nature of the experimental patterns are the same as predicted by the Turing couple (cAMP, ATP). Embryological polarity and convergent extension are based on polar eigenfunction and saddle-shaped eigenfunction, respectively.

Animals↗
PubMed2005

Lifestyle-related risks: are trends in Europe converging?

OBJECTIVES: What has become of lifestyle differences in a united Europe, where member states become more and more similar on aspects such as welfare systems and population dynamics? In this paper, we try to answer the question whether the gap in lifestyle-related risk factors in Europe has narrowed over the past 30-40 years. METHODS: Smoking, alcohol consumption, physical activity, obesity and food consumption all have an impact on cancer, cardiovascular disease and other non-communicable diseases. Databases of Eurostat, OECD (Organisation for Economic Co-operation and Development) and the World Health Organisation were screened for data on lifestyle-related risk factors in the European Union, and a literature search was performed for studies that collected international comparable data about the selected factors. RESULTS: The gap in European lifestyle has narrowed over the past 30-40 years for smoking (women), alcohol consumption and total fat intake. For fruit and vegetable consumption, convergence is not occurring. For some risk factors, such as smoking and obesity, intranational differences surpass the international differences. CONCLUSIONS: The results support the notion of convergent lifestyles among Europeans over time. We also found that there is a serious lack of reliable data on lifestyle-related risk factors that are suitable for international comparison. It is essential to invest in reliable and internationally comparable data, obtained according to best evidence, to get more insight into real differences regarding risk factors in Europe. The European Public Health programme may be an opportunity to realize these goals.

Age Factors↗
PubMed2004

Van Gogh-like2 (Strabismus) and its role in planar cell polarity and convergent extension in vertebrates.

In the past two years, studies of Stbm genes (also known as Vangl2) and the proteins that they encode in mice, flies, frogs and fish have shown that they have a crucial role in regulating planar cell polarity and convergent extension movements. Combined genetic and biochemical analyses have pointed to signaling pathways where Stbm (Vangl2) proteins might act, and have identified several interacting proteins that form a crucial multi-protein signaling complex at the membrane. These studies show that these proteins have a pivotal role in a signaling cascade(s) that has been highly conserved in evolution. This review will summarize recent findings documenting the involvement of Stbm (Vangl2) and associated proteins in planar cell polarity, non-canonical Wnt signaling and convergent extension movements.

Animals↗
PubMed2005

Xenopus p21-activated kinase 5 regulates blastomeres' adhesive properties during convergent extension movements.

The p21-activated kinase (PAK) proteins regulate many cellular events including cell cycle progression, cell death and survival, and cytoskeleton rearrangements. We previously identified X-PAK5 that binds the actin and microtubule networks, and could potentially regulate their coordinated dynamics during cell motility. In this study, we investigated the functional importance of this kinase during gastrulation in Xenopus. X-PAK5 is mainly expressed in regions of the embryo that undergo extensive cell movements during gastrula such as the animal hemisphere and the marginal zone. Expression of a kinase-dead mutant inhibits convergent extension movements in whole embryos and in activin-treated animal cap by modifying behavior of cells. This phenotype is rescued in embryo by adding back X-PAK5 catalytic activity. The active kinase decreases cell adhesiveness when expressed in animal hemisphere and inhibits the calcium-dependent reassociation of cells, while dead X-PAK5 kinase localizes to cell-cell junctions and increases cell adhesion. In addition, endogenous X-PAK5 colocalizes with adherens junction proteins and its activity is regulated by extracellular calcium. Taken together, our results suggest that X-PAK5 regulates convergent extension movements in vivo by modulating the calcium-mediated cell-cell adhesion.

Adherens Junctions↗
PubMed2005

Combinatorial activity of Flamingo proteins directs convergence and extension within the early zebrafish embryo via the planar cell polarity pathway.

The seven-transmembrane protocadherin, Flamingo, functions in a number of processes during Drosophila development, including planar cell polarity (PCP). To assess the role(s) of Flamingo1/Celsr1 (Fmi1) during vertebrate embryogenesis we have exploited the zebrafish system, identifying two Fmi1 orthologues (zFmi1a and zFmi1b) and employing morpholinos to induce mis-splicing of zebrafish fmi1 mRNAs, to both imitate mutations identified in Drosophila flamingo and generate novel aberrant Flamingo proteins. We demonstrate that in the zebrafish gastrula, Fmi1 proteins function in concert with each other and with the vertebrate PCP proteins, Wnt11 and Strabismus, to mediate convergence and extension during gastrulation, without altering early dorso-ventral patterning. We show that zebrafish Fmi1a promotes extension of the entire antero-posterior axis of the zebrafish gastrula including prechordal plate and ventral diencephalic precursors. However, while we show that control over axial extension is autonomous, we find that Fmi1a is not required within lateral cells undergoing dorsal convergence.

Animals↗
PubMed2005

Confrontation of morphological and molecular data: the Praomys group (Rodentia, Murinae) as a case of adaptive convergences and morphological stasis.

Phylogenetic relationships in a group of 21 African rodent species designated as the Praomys group (Murinae) were investigated using morphological characters and sequence data from the complete mitochondrial cytochrome b gene and nuclear IRBP gene fragment (840bp). The molecular results confirm the monophyly of the Praomys group, including the species Malacomys verschureni, while the other Malacomys species appear very divergent. The basal relationships within the Praomys group are poorly resolved, suggesting a rapid radiation at about 7-9 million years ago based on genetic divergence rates calibrated from the fossil record. Discrepancies between molecular and morphological results probably reflect of numerous convergences as well as variations in the rates of morphological evolution among lineages. Reconstructions of the ancestral character states suggest a savannah origin for the Praomys group, along with some morphological traits conserved by stasis in savannah taxa. At the same time, forest taxa seem to be characterized by an accelerated morphological evolution, with acquisition of convergent adaptive characters.

Adaptation, Biological↗
PubMed2006

Phylogenetic relationships and convergence of helicosporous fungi inferred from ribosomal DNA sequences.

Helicosporous fungi form elegant, coiled, and multicellular mitotic spores (conidia). In this paper, we investigate the phylogenetic relationships among helicosporous fungi in the asexual genera Helicoma, Helicomyces, Helicosporium, Helicodendron, Helicoon, and in the sexual genus Tubeufia (Tubeufiaceae, Dothideomycetes, and Ascomycota). We generated ribosomal small subunit and partial large subunit sequences from 39 fungal cultures. These and related sequences from GenBank were analyzed using parsimony, likelihood, and Bayesian analysis. Results showed that helicosporous species arose convergently from six lineages of fungi in the Ascomycota. The Tubeufiaceae s. str. formed a strongly supported monophyletic lineage comprising most species from Helicoma, Helicomyces, and Helicosporium. However, within the Tubeufiaceae, none of the asexual genera were monophyletic. Traditional generic characters, such as whether conidiophores were conspicuous or reduced, the thickness of the conidial filament, and whether or not conidia were hygroscopic, were more useful for species delimitation than for predicting higher level relationships. In spite of their distinctive, barrel-shaped spores, Helicoon species were polyphyletic and had evolved in different ascomycete orders. Helicodendron appeared to be polyphyletic although most representatives occurred within Leotiomycetes. We speculate that some of the convergent spore forms may represent adaptation to dispersal in aquatic environments.

DNA, Ribosomal↗
PubMed2002

Rectus eye muscle paths after surgical correction of convergent strabismus fixus.

PURPOSE: To present a new surgical procedure for convergent strabismus fixus. DESIGN: Interventional case report. METHODS: A 69-year-old woman was referred to us because of esotropia of both eyes. Both eyes were fixed in a position of extreme adduction, and ocular motility was severely restricted in all directions. Magnetic resonance imaging demonstrated that the superior rectus (SR) was deviated nasally and the lateral rectus (LR) was deviated inferiorly. We performed operations for both eyes consisting of hemitranspositions of the SR and LR combined with a large recession of the medial rectus. RESULTS: Postoperatively, the patient became able to fixate in primary gaze and ocular motility markedly improved in all directions. Magnetic resonance imaging confirmed that the paths of the SR and LR were corrected. CONCLUSIONS: This surgical procedure appears to be a useful option for treating convergent strabismus fixus.

Aged↗
PubMed1998

The convergent validity of the Phobia Origins Questionnaire (POQ): a review of the evidence.

The Phobic Origins Questionnaire (POQ) [Ost, L.-G. & Hugdahl, K. (1981). Acquisition of phobias and anxiety response patterns in clinical patients. Behaviour Research and Therapy, 19, 439-447.] is the most commonly cited instrument for determining the origins of phobic anxiety and data obtained using this instrument strongly support the role of conditioning in the acquisition of fear reactions. The construct validity of the POQ in assessing episodes of conditioning has been questioned [e.g. Menzies, R. G. & Clarke, J. C. (1994). Retrospective studies of the origins of phobias: a review. Anxiety, Stress and Coping, 7, 305-318.] This paper examined the convergent validity of the POQ by comparing origins' classifications based on the POQ to classifications based on alternative instruments. The convergent validity of the POQ was found to be extremely poor. The POQ was consistently associated with a much greater likelihood of classifying the origin of fear reactions as due to direct conditioning episodes than was found using alternative instruments. The findings question the usefulness of the POQ in examining the origins of phobic anxiety.

Conditioning, Psychological↗