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At least 163 records · Page 9Linked to original sources
PubMed1991

Use of radiofrequency current to ablate accessory connections in children.

BACKGROUND: Several investigators have recently ablated electrophysiologically mapped accessory connections in the adult human myocardium by using radiofrequency current. To examine the effectiveness and safety of radiofrequency current for ablation of accessory connections in children, 20 consecutive patients (age, 3-18 years) with preexcitation and/or supraventricular tachycardia were evaluated by electrophysiological study. METHODS AND RESULTS: Nineteen of the 20 patients were completely studied and demonstrated accessory connections. After identification of the earliest retrograde atrial activation site, a steerable 7F catheter (with a 4-mm-long electrode at the distal tip) was placed within the ventricular cavity ipsilateral to the accessory connection and positioned at the atrioventricular valve annulus directly opposite the earliest point of retrograde atrial activation. Radiofrequency current was delivered at 50-65 volts for 10-60 seconds at a frequency of 500 kHz. Radiofrequency pulses were delivered for two to 26 trials. Upon completion of radiofrequency trials, repeat electrophysiological testing was performed. Thirteen of 19 subjects (68%) experienced definite successful ablation of their accessory pathway; an additional patient had probable successful ablation, yielding an overall success rate of 74%. Eighty-seven percent of individuals with a left-sided pathway had permanent ablation and 100% with a manifest left-sided pathway experienced successful ablation. Only 29% of the first seven patients had a successful result; in contrast, 92% of the next 12 patients had successful interruption of their accessory pathways. After ablation, 4-day continuous electrocardiographic telemetry disclosed no significant arrhythmias. CPK enzyme rises peaked at 12-24 hours. The rise was excessive and associated with general anesthesia in five patients. The isoenzyme MB fraction rose mildly in five other patients and returned to normal within 72 hours. No clinical or electrocardiographic evidence of myocardial ischemia was detected. Follow-up for 4-12 months indicates no return of preexcitation or tachycardia in any patient whose accessory connection was successfully ablated. CONCLUSIONS: This experience indicates that radiofrequency current is an effective and safe technique for ablation of accessory connections in children.

Adolescent↗
PubMed1996

Functional organization for direction of motion and its relationship to orientation maps in cat area 18.

The goal of this study was to explore the functional organization of direction of motion in cat area 18. Optical imaging was used to record the activity of populations of neurons. We found a patchy distribution of cortical regions exhibiting preference for one direction over the opposite direction of motion. The degree of clustering according to preference of direction was two to four times smaller than that observed for orientation. In general, direction preference changed smoothly along the cortical surface; however, discontinuities in the direction maps were observed. These discontinuities formed lines that separated pairs of patches with preference for opposite directions. The functional maps for direction and for orientation preference were closely related; typically, an iso-orientation patch was divided into regions that exhibited preference for opposite directions, orthogonal to the orientation. In addition, the lines of discontinuity within the direction map often connected points of singularity in the orientation map. Although the organization of both domains was related, the direction and the orientation selective responses were separable; whereas the selective response according to direction of motion was nearly independent of the length of bars used for visual stimulation, the selective response to orientation decreased significantly with decreasing length of the bars. Extensive single and multiunit electrical recordings, targeted to selected domains of the functional maps, confirmed the features revealed by optical imaging. We conclude that significant processing of direction of motion is performed early in the cat visual pathway.

Age Factors↗
PubMed2003

DTI mapping of human brain connectivity: statistical fibre tracking and virtual dissection.

Several approaches have been used to trace axonal trajectories from diffusion MRI data. If such techniques were first developed in a deterministic framework reducing the diffusion information to one single main direction, more recent approaches emerged that were statistical in nature and that took into account the whole diffusion information. Based on diffusion tensor MRI data coming from normal brains, this paper presents how brain connectivity could be modelled globally by means of a random walk algorithm. The mass of connections thus generated was then virtually dissected to uncover different tracts. Corticospinal, corticobulbar, and corticothalamic tracts, the corpus callosum, the limbic system, several cortical association bundles, the cerebellar peduncles, and the medial lemniscus were all investigated. The results were then displayed in the form of an in vivo brain connectivity atlas. The connectivity pattern and the individual fibre tracts were then compared to known anatomical data; a good matching was found.

Algorithms↗
PubMed1999

Evaluation of the Information Sources Map.

As part of preliminary studies for the development of a digital library, we have studied the possibility of using the UMLS Information Sources Map (ISM) database to provide the means to connect and map different terminologies, as well as to facilitate access to available information sources. The main issues discussed are the indexing of and connection to relevant online sources. We found the features of the ISM to be consistent with the need to support automated source selection and retrieval. However, attention should be paid to three aspects of the information: granularity, completeness, and accuracy. We found the ISM to be potentially useful; however, significant modifications will be required if the ISM is to be able to support automated source selection and retrieval.

Abstracting and Indexing↗
PubMed2000

Fluid mechanic assessment of the total cavopulmonary connection using magnetic resonance phase velocity mapping and digital particle image velocimetry.

The total cavopulmonary connection (TCPC) is currently the most promising modification of the Fontan surgical repair for single ventricle congenital heart disease. The TCPC involves a surgical connection of the superior and inferior vena cavae directly to the left and right pulmonary arteries, bypassing the right heart. In the univentricular system, the ventricle experiences a workload which may be reduced by optimizing the cavae-to-pulmonary anastomosis. The hypothesis of this study was that the energetic efficiency of the connection is a consequence of the fluid dynamics which develop as a function of connection geometry. Magnetic resonance phase velocity mapping (MRPVM) and digital particle image velocimetry (DPIV) were used to evaluate the flow patterns in vitro in three prototype glass models of the TCPC: flared zero offset, flared 14 mm offset, and straight 21 mm offset. The flow field velocity along the symmetry plane of each model was chosen to elucidate the fluid mechanics of the connection as a function of the connection geometry and pulmonary artery flow split. The steady flow experiments were conducted at a physiologic cardiac output (4 L/min) over three left/right pulmonary flow splits (70/30, 50/50, and 30/70) while keeping the superior/inferior vena cavae flow ratio constant at 40/60. MRPVM, a noninvasive clinical technique for measuring flow field velocities, was compared to DPIV, an established in vitro fluid mechanic technique. A comparison between the results from both techniques showed agreement of large scale flow features, despite some discrepancies in the detailed flow fields. The absence of caval offset in the flared zero offset model resulted in significant caval flow collision at the connection site. In contrast, offsetting the cavae reduced the flow interaction and caused a vortex-like low velocity region between the caval inlets as well as flow disturbance in the pulmonary artery with the least total flow. A positive correlation was also found between the direct caval flow collision and increased power losses. MRPVM was able to elucidate these important fluid flow features, which may be important in future modifications in TCPC surgical designs. Using MRPVM, two- and three-directional velocity fields in the TCPC could be quantified. Because of this, MRPVM has the potential to provide accurate velocity information clinically and, thus, to become the in vivo tool for TCPC patient physiological/functional assessment.

Biomedical Engineering↗
PubMed1994

Experience-dependent mechanism of binocular map plasticity in Xenopus: incongruent connections are masked by retinal input.

When one eye in larval Xenopus is rotated to change the orientation of its visual map on the contralateral tectum, the map from the other eye to the same tectum can subsequently alter its orientation to match the rotated input. This plasticity re-establishes binocular congruence between the two maps and involves an experience-dependent reorganization of functional connections in the crossed isthmotectal projection, which delivers the ipsilateral eye's map to the tectum. Here, recordings were made at the same tectal sites in 8 eye-rotated frogs immediately before and after removing the rotated retina. All had congruent binocular maps prior to enucleation, with matching receptive fields in the two eyes at each recording site. In 5 frogs, eye removal unmasked additional, incongruent receptive fields in the ipsilateral eye, recorded from previously undetectable crossed isthmotectal connections occupying their original positions in the tectum. This result suggests that the plasticity also involves functional suppression of binocularly-incongruent inputs from the ipsilateral eye by retinotectal afferents.

Animals↗
PubMed2002

Morphological characterization of in vitro neuronal networks.

We use in vitro neuronal networks as a model system for studying self-organization processes in the nervous system. We follow the neuronal growth process, from isolated neurons to fully connected two-dimensional networks. The mature networks are mapped into connected graphs and their morphological characteristics are measured. The distributions of segment lengths, node connectivity, and path length between nodes, and the clustering coefficient of the networks are used to characterize network morphology and to demonstrate that our networks fall into the category of small-world networks.

Animals↗
PubMed1997

Connectivity and management of caribbean coral reefs

Surface current patterns were used to map dispersal routes of pelagic larvae from 18 coral reef sites in the Caribbean. The sites varied, both as sources and recipients of larvae, by an order of magnitude. It is likely that sites supplied copiously from "upstream" reef areas will be more resilient to recruitment overfishing, less susceptible to species loss, and less reliant on local management than places with little upstream reef. The mapping of connectivity patterns will enable the identification of beneficial management partnerships among nations and the design of networks of interdependent reserves.

Journal Article↗
PubMed2003

Functional topography of connections linking mirror-symmetric maps in the mouse olfactory bulb.

In rodents, each main olfactory bulb contains two mirror-symmetric glomerular maps, a feature not found in the initial topographic maps of other sensory systems. Targeting tracer injections to identified glomeruli revealed that isofunctional odor columns-translaminar assemblies connected to a given glomerulus-were specifically and reciprocally interconnected through a mutually inhibitory circuit with exquisite topographic specificity. Thus, instead of containing two mirror-symmetric maps, we propose that the olfactory bulb contains a single integrated map in which isofunctional odor columns are connected through an intrabulbar link, analogous to the specific horizontal connections linking iso-orientation columns in primary visual cortex.

Animals↗
PubMed1985

Mapping of transmitter-specific connections: simultaneous demonstration of anterograde degeneration and changes in the immunostaining pattern induced by lesions.

This paper describes simple procedures which allow immunohistochemistry to be combined with a newly developed silver degeneration technique for the purpose of mapping transmitter-specific connections on the light microscopic level. Conditions of fixation, survival time and immunohistochemistry that contribute to optimal results are discussed.

Animals↗
PubMed1999

Making brain connections: neuroanatomy and the work of TPS Powell, 1923-1996.

Dr. Thomas PS Powell was one of the founders of modern neuroanatomy. His career spanned an era that saw techniques for analyzing connections in the central nervous system dramatically increase in number and resolving power. In tracing the history of his research, one can see how the introduction of each new technique provided an incremental step in analytical capacity although eventually revealing its own limitations. Also evident is the extent to which prejudices born in the days of applying earlier techniques could continue to influence the interpretation of results obtained with new ones. Powell's contributions to neuroscience were extremely wide-ranging, encompassing investigations of the circuitry of the basal ganglia, corticofugal connections, topographic maps in sensory systems, central olfactory pathways, corticocortical and commissural connections, and pathways for sensory convergence in the cerebral cortex. From these investigations, made with tract tracing techniques, much existing knowledge of forebrain organization is derived. He was also one of the earliest investigators to use electron microscopy in the investigation of the central nervous system, and his electron microscopic studies on the olfactory bulb, thalamus, cerebral cortex, and basal ganglia laid, to a large extent, the foundations for all modern research on the synaptic circuitry of these structures. He was given to synthesizing data across systems in order to arrive at common principles of brain organization. A number of these syntheses have been sources of great interest and, occasionally, controversy.

Animals↗
PubMed1993

MAP kinase kinase: a node connecting multiple pathways.

Numerous studies have been published these last few years on the involvement of MAP kinases in signal transduction reflecting their importance in cell cycle and cell growth controls. The identification and the characterization of their direct upstream activator has considerably enlarged our understanding of the phosphorylation network. The MAP kinase kinases (MAPKKs) are dual-specificity protein kinases which phosphorylate and activate MAP kinases. To date, MAPKK homologues have been found in yeast, invertebrates, amphibians, and mammals. Moreover, the MAPKK/MAPK phosphorylation switch constitutes a basic module activated in distinct pathways in yeast and in vertebrates. MAPKK regulation studies have led to the discovery of at least four MAPKK convergent pathways in higher organisms. One of these is similar to the yeast pheromone response pathway which includes the ste11 protein kinase. Two other pathways require the activation of either one or both of the serine/threonine kinase-encoded oncogenes c-Raf-1 and c-Mos. Additionally, recent studies suggest a possible effect of the cell cycle control regulator cyclin-dependent kinase 1 (cdc2) on MAPKK activity. Finally, MAPKKs seem to be essential transducers through which signals must pass before reaching the nucleus.

Amino Acid Sequence↗
PubMed2002

Initial demonstration of in vivo tracing of axonal projections in the macaque brain and comparison with the human brain using diffusion tensor imaging and fast marching tractography.

Diffusion tensor imaging (DTI), a magnetic resonance imaging technique, is used to infer major axonal projections in the macaque and human brain. This study investigates the feasibility of using known macaque anatomical connectivity as a "gold-standard" for the evaluation of DTI tractography methods. Connectivity information is determined from the DTI data using fast marching tractography (FMT), a novel tract-tracing (tractography) method. We show for the first time that it is possible to determine, in an entirely noninvasive manner, anatomical connection pathways and maps of an anatomical connectivity metric in the macaque brain using a standard clinical scanner and that these pathways are consistent with known anatomy. Analogous human anatomical connectivity is also presented for the first time using the FMT method, and the results are compared. The current limitations of the methodology and possibilities available for further studies are discussed.

Animals↗
PubMed2002

MAP kinase module: the Ksr connection.

Ksr has been genetically defined as a component of the Ras/MAP kinase pathway, but its role has been unclear. New studies now provide evidence that Ksr is important for signal transmission within the MAP kinase module, where it apparently acts as a location-regulated scaffold connecting MEK to Raf.

Animals↗
PubMed2001

Structural connectivity in white matter using the projected diffusion-tensor distance.

Diffusion tensor imaging (DTI) has become a powerful tool for analyzing the structure of white matter. We have proposed a method for detecting nerve fiber bundles in white matter using diffusion tensor images and have applied the method to in vivo brain measurements. Although there are many methods to investigate the connectivity of white matter that are based on principal eigenvector or full tensor propagation. In the proposed method, we use directional diffusion measurements to infer regional white matter connectivity. To assess the connectivity, we compose the map based on the projected tensor distance, then we put a label on the constructed map and segment regionally connected white matter using labels. The purpose of this study is to obtain a quantitative map of white matter connectivity in vivo using diffusion tensor properties.

Algorithms↗
PubMed1979

Connections and visual-field mapping in cat's tectoparabigeminal circuit.

1. The aim of these experiments was to analyze the organization of the reciprocal connections between the cat's superior colliculus and parabigeminal nucleus. Both physiological and anatomical techniques were employed. 2. A population of cells in the superficial gray and upper optic layers of the colliculus was labeled retrogradely by horseradish peroxidase injections into the parabigeminal nucleus. No other sources of input to the nucleus were found in the brain stem or diencephalon. 3. A map of the visual field within the parabigeminal nucleus was reconstructed by plotting visual receptive fields at 350 parabigeminal sites with microelectrodes. The map resembled that found in the colliculus, although it was considerably less orderly. The entire contralateral visual field was represented and, in addition, roughly the central 40 degrees of the ipsilateral hemifield was included; futhermore, the expansion of the central visual field was similar to that of the tectal map. 4. The return parabigeminal projections to the caudal parts of the two colliculi, representing the contralateral hemifields, were in register with the tectal visual-field maps. In contrast, the parabigeminal pathways to the anterior segments of the two colliculi, representing part of the ipsilateral visual fields, were not clearly topographic. The projection to this part of the contralateral colliculus showed little order, while that to the ipsilateral colliculus was extremely sparse. 5. A single site in the colliculus can be the target of axons from nonhomologous locations in the two parabigeminal nuclei; so that both parabigeminal inputs are in register with the tectal map.

Animals↗
PubMed2001

Dendritic subunits determined by dendritic morphology.

A theoretical framework is presented in which arbitrarily branched dendritic structures with nonhomogeneous membrane properties and nonuniform geometry can be transformed into an equivalent unbranched structure (equivalent cable). Rall's equivalent cylinder is seen to be one part of the equivalent cable in the special case of dendrites satisfying the Rall criteria. The relation between the branched dendrite and its equivalent unbranched representation is uniquely defined by an invertible mapping that connects configurations of inputs on the branched structure with those on the unbranched structure, and conversely. This mapping provides a new definition of dendritic subunit and provides a mechanism for characterizing local and nonlocal signal processing within dendritic structures.

Animals↗