[A method for the elimination of errors connected with the vertical diffusion technic used for the determination of active INH in the blood serum].
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Biological Transport↗
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The functional organization of local circuits in visual cortex: insights from the study of tree shrew striate cortex.
We have used a combination of anatomical and physiological techniques to explore the functional organization of vertical and horizontal connections in tree shrew striate cortex. Our studies of vertical connections reveal a remarkable specificity in the laminar arrangement of the projections from layer IV to layer III that establishes three parallel intracortical pathways. The pathways that emerge from layer IV are not simple continuations of parallel thalamocortical pathways. Layer IV and its connections with layer II/III restructure the inputs from the LGN, combining the activity from ON and OFF channels and from the left and right eye and transmit the products of this synthesis to separate strata within the overlying layers. In addition, studies of two other prominent vertical connection pathways, the projections from layer VI to layer IV and from layer II/III to layer V suggest that the parallel nature of these systems is perpetuated throughout the cortical depth. Our studies of horizontal connections have revealed a systematic relationship between a neuron's orientation preference and the distribution of its axon arbor across the cortical map of visual space. Horizontal connections in layer II/III extend for greater distances and give rise to a greater number of terminals along an axis of the visual field map that corresponds to the neuron's preferred orientation. These findings suggest that the contribution of horizontal inputs to the response properties of layer II/III neurons is likely to be greater in regions of visual space that lie along the axis of preferred orientation (endzones) than along the orthogonal axis (side zones). Topographically aligned horizontal connections may contribute to the orientation preference of layer II/III neurons and could account for the axial specificity of some receptive field surround effects. Together, these results emphasize that specificity in the spatial arrangement of local circuit axon arbors plays an important role in shaping the response properties of neurons in visual cortex.
Animals↗
Mixing patterns in networks.
We study assortative mixing in networks, the tendency for vertices in networks to be connected to other vertices that are like (or unlike) them in some way. We consider mixing according to discrete characteristics such as language or race in social networks and scalar characteristics such as age. As a special example of the latter we consider mixing according to vertex degree, i.e., according to the number of connections vertices have to other vertices: do gregarious people tend to associate with other gregarious people? We propose a number of measures of assortative mixing appropriate to the various mixing types, and apply them to a variety of real-world networks, showing that assortative mixing is a pervasive phenomenon found in many networks. We also propose several models of assortatively mixed networks, both analytic ones based on generating function methods, and numerical ones based on Monte Carlo graph generation techniques. We use these models to probe the properties of networks as their level of assortativity is varied. In the particular case of mixing by degree, we find strong variation with assortativity in the connectivity of the network and in the resilience of the network to the removal of vertices.
Journal Article↗
Total anomalous pulmonary venous connection to the left vertical vein. A plain-film sign useful in early diagnosis.
Total anomalous pulmonary venous connection to the left vertical vein often may be recognized on the plain postero-anterior chest radiograph by the characteristic supracardiac shadow. This "snowman sign" is useful in older patients but rarely is apparent in infancy. In such young patients the authors have discovered a density anterior to the trachea on the lateral chest radiograph. This finding is present prior to the appearance of the snowman sign and should prove useful in the early diagnosis of this anomaly, facilitating prompt, appropriate treatment. Five representative cases are tabulated and developmental and clinical aspects are reviewed.
Child↗
Scale invariance in road networks.
We study the topological and geographic structure of the national road networks of the United States, England, and Denmark. By transforming these networks into their dual representation, where roads are vertices and an edge connects two vertices if the corresponding roads ever intersect, we show that they exhibit both topological and geographic scale invariance. That is, we show that for sufficiently large geographic areas, the dual degree distribution follows a power law with exponent 2.2< or = alpha < or =2.4, and that journeys, regardless of their length, have a largely identical structure. To explain these properties, we introduce and analyze a simple fractal model of road placement that reproduces the observed structure, and suggests a testable connection between the scaling exponent and the fractal dimensions governing the placement of roads and intersections.
Journal Article↗
A 3D deformable surface model for segmentation of objects from volumetric data in medical images.
In this paper we present a new 3D discrete dynamic surface model. The model consists of vertices and edges, which connect adjacent vertices. Basic geometry of the model surface is generated by triangle patches. The model deforms by internal and external forces. Internal forces are obtained from local geometry of the model and are related to the local curvature of the surface. External forces, on the other hand, are based on the image data and are calculated from desired image features. We also present a method for generating an initial volume for the model from a stack of initial contours, drawn by the user on cross sections of the volumetric data.
Algorithms↗
The evolution of network topology by selective removal.
The topology of large social, technical and biological networks such as the World Wide Web or protein interaction networks has caught considerable attention in the past few years (reviewed in Newman 2003), and analysis of the structure of such networks revealed that many of them can be classified as broad-tailed, scale-free-like networks, since their vertex connectivities follow approximately a power-law. Preferential attachment of new vertices to highly connected vertices is commonly seen as the main mechanism that can generate scale-free connectivity in growing networks (Watts 2004). Here, we propose a new model that can generate broad-tailed networks even in the absence of network growth, by not only adding vertices, but also selectively eliminating vertices with a probability that is inversely related to the sum of their first- and second order connectivity.
Animals↗
Multiple subpial transection: a new approach to the surgical treatment of focal epilepsy.
A new operative approach has been designed for the relief of medically intractable focal epilepsy. It is intended particularly to be used in those cases where the epileptogenic lesion lies in "unresectable" cortex; that is, those cerebral regions subserving speech, memory, and primary motor and sensory function. The procedure is based upon experimental evidence indicating 1) that epileptogenic discharge requires substantial side-to-side or horizontal interaction of cortical neurons, and 2) that the major functional properties of cortical tissue depend upon the vertical fiber connections of the columnar units. The technique requires severing of tangential intracortical fibers while preserving the vertical fiber connections of both incoming and outgoing nerve pathways and of the penetrating blood vessels which also have a vertical orientation. In this study, the effect of multiple subpial transection was assessed on both function and seizure control. The effect on function was reviewed in 32 cases; only 20 cases were evaluated with respect to seizure control, since a follow-up period of 5 years or more (5 to 22 years) is required before conclusions can be drawn. Multiple subpial transection was applied to the precentral gyrus in 16 cases, the postcentral gyrus in six, Broca's area in five, and Wernicke's area in five. With respect to function, the major finding was that none of the 32 patients has suffered a clinically significant behavioral deficit (although subtle deficits could be detected by careful neurological examination). Complete control of seizures has been obtained in 11 (55%) of the 20 cases evaluated. Nine patients developed recurrent seizures consequent to progressive disease unsuspected before operation (Rasmussen's encephalitis in five, tumor in three, and subacute sclerosing panencephalitis in one). In none of these cases, however, did the recurrent seizures arise in the transected zone. Thus, the results indicate that multiple subpial transection is about as effective as standard excisional therapy, and can be successfully employed when epileptogenic lesions encroach upon cortical territories, the removal of which would be functionally incapacitating.
Adolescent↗
Anomalous percolation properties of growing networks.
We describe the anomalous phase transition of the emergence of the giant connected component in scale-free networks growing under mechanism of preferential linking. We obtain exact results for the size of the giant connected component and the distribution of vertices among connected components. We show that all the derivatives of the giant connected component size S over the rate b of the emergence of new edges are zero at the percolation threshold b(c), and S infinity exp[-d(gamma)(b-b(c))(-1/2)], where the coefficient d is a function of the degree distribution exponent gamma. In the entire phase without the giant component, these networks are in a "critical state." The probability P(k) that a vertex belongs to a connected component of a size k is of a power-law form. At the phase transition point, P(k) approximately 1/(k ln k)(2). In the phase with the giant component, P(k) has an exponential cutoff at k(c) approximately 1/S. In the simplest particular case, we present exact results for growing exponential networks.
Journal Article↗
Shape constancy from novel views.
Prior experiments on shape constancy from novel views are inconclusive: Some show that shapes of objects can be recognized reliably from novel views, whereas others show just the opposite. Our analysis of prior results suggests that shape constancy from novel views is reliable when the object has properties that constrain its shape: The object has volumetric primitives, it has surfaces, it is symmetrical, it is composed of geons, its contours are planar, and its images provide useful topological information about its three-dimensional structure. To test the role of some of these constraints, we performed a set of experiments. Solid shapes (polyhedra) were shown on a computer monitor by means of kinetic depth effect. Experiment 1 showed that shape constancy can be reliably achieved when a polyhedron is represented by its contours (most of the constraints are present), but not when it is represented by vertices or by a polygonal line connecting the vertices in a random order (all the constraints are absent). Experiments 2 and 3 tested the role of individual constraints. Results of these experiments show that shape constancy from novel views is reliable when the object has planar contours and when the shapes of the contours together with topological information about the relations among the contours constrain the possible interpretations of the shape. Symmetry of the object and the topological stability of its image also contribute to shape constancy.
Form Perception↗
Comparative and functional morphology of the stomach in the adult and newborn pigmy hippopotamus (Choeropsis liberiensis).
Examination of the topographical anatomy of the stomach complex and intestinal tract of an adult male and a newborn female pigmy hippopotamus (Choeropsis liberiensis) shows that the stomach consists of four chambers, the first three constituting the proventriculus and the fourth the glandular stomach. The proventriculus is made up of a visceral and parietal blind sac opening into a connecting chamber, which in turn opens into the glandular compartment. The walls of the proventricular chambers are covered with villi and non-glandular mucous membrane. The significant difference between the animals is that whereas the connecting chamber of the adult stomach lies transversely deep in the cranial part of the abdomen and connects with the glandular chamber on the right side, that of the newborn lies almost vertically and connects ventrally with the glandular compartment situated on the floor of the abdomen. A groove which in the adult runs more or less horizontally from the cardia through the visceral sac and connecting chambers is aligned almost vertically in the newborn. In the adult the connecting chamber is the largest compartment, but in the neonate the visceral blind sac and the glandular compartment are proportionally larger. Functional aspects of these anatomical differences are discussed in relation to suckling behavior.(ABSTRACT TRUNCATED AT 250 WORDS)
Animals↗
Cortical and callosal connections concerned with the vertical meridian of visual fields in the cat.
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Animals↗
Induction of a regular nuclear lattice by overexpression of NuMA.
Transient overexpression of nuclear mitotic apparatus protein (NuMA) in HeLa cells results in ordered lattices which can fill the nucleus and which are stable to detergent extraction. Electron microscopy reveals a quasi-hexagonal organization with an average spacing between the vertices of approximately 170 nm and short 6-nm-diameter rods connecting the vertices. Overexpression of a NuMA construct with an in-frame addition in the coiled-coil domain shows hexagons with the spacing increased by 42% while constructs with deletions in the coiled-coil domain yield hexagons with the spacing decreased by 40 and 19%. NuMA constructs truncated at residue 2005 or 2030 in the tail domain cause a drastic reorganization of nuclear components with relocation of the DNA, histone H1, and nucleoli to the nuclear rim. A construct lacking the head and much of the coiled-coil region also affects nuclear organization. In contrast, NuMA constructs truncated at residue 1950 or 1935 which lack the nuclear localization signal display normal nuclear structure but form cytoplasmic aggregates which also display hexagonal organization. Immunoelectron microscopy confirms that the nuclear lattices are built from NuMA. We discuss the importance of the different domains of NuMA for building the ordered in vivo lattices and whether NuMA could play a structural role in the architecture of the normal interphase nucleus.
Antigens, Nuclear↗
[Transobturator correction of cystocele].
OBJECTIVE: We present our initial experience with the Perigee system for anterior vaginal wall prolapses repair. MATERIAL AND METHOD: 15 patients with anterior vaginal wall prolapse (mean age: 62 years old) underwent implanted with Perigee system which is composed by a mesh for correcting central defect and four self-attached horns for correcting lateral defect. The implanted procedure consist of four steps: 1) lateral vaginal wall dissection as far as isquiopubic branch; 2) performance of two upper marks at genitofemoral fold and two lower marks at 2 cm laterally and 3 cm lower; 3) insertion of the upper needles parallel to the isquiopubic branch and connection with the mesh's "arms" plus insertion of the lower needles vertically and connection with mesh's "legs"; 4) to adjust the mesh free tension. The system POP-Q was used as an objective measure of correction rate. RESULTS: Preoperatively, the point Aa was 0.09. After 6 weeks and three months postoperatively was -3.00 and -2.73 respectively. Preoperatively, the point Ba was 1.73. After 6 weeks and three months postoperatively was -2.82 and -2.82 respectively. No major complications were presented. No vascular damage or significant bleeding was observed. CONCLUSION: The transobturator correction of cystocele is an attractive alternative. The initial good outcome may be expected to be long lasting.
Adult↗
[The anatomy of the pelvis].
The pelvis consists of the sacrum, the ossa coxae, and additionally the ligaments between these bones. According to mathematical calculations the bony structure as well as the arrangement of ligaments result in optimal engineering principles, i.e. maximal strength is achieved by minimal principles, i.e. maximal strength is achieved by minimal material. The muscles inside the pelvis are covered by a fascial layer. The latter represents a continuation of the abdominal transversal fascia which extends to the pelvic floor. The connective tissue fibres around the pelvic viscera interweave with those of the pelvic floor and laterally with the connective tissue around vessels and nerves. Connective tissue around the neurovascular sheaths is nearly transversely arranged and forms the lateral ligaments of bladder, uterus or prostate gland and the rectum. Several vertically arranged connective tissue ligaments accompany either the superior rectal artery and hypogastric nerves or the ureter and the ovarian vessels. Therefore, the lymphatic fluid of the pelvic organs passes the aortic lymph nodes and/or to the lateral pelvic wall along the branches of the internal iliac vessels.
Humans↗
Development of local circuits in human visual cortex.
How we see the world largely depends on the organization of neuronal circuits in visual cortex. Physiological recordings in mammals indicate that circuits develop over a period that extends well into early postnatal ages (LeVay et al., 1980; Albus and Wolf, 1984). Our understanding of how these circuits are assembled during development is still fragmentary (Katz and Callaway, 1992). Here we describe the development of local connections within visual cortex, using the fluorescent dye 1,1'-dioctadecyl-3,3,3',3'-tetramethylindocarbocyanine perchlorate to trace axonal projections in post-mortem human brains. Vertical (intracolumnar) connections between layers 2/3 and 5, which link neurons representing the same point in the visual field, develop prenatally at 26-29 weeks gestation. In contrast, horizontal (intercolumnar) connections between different points in the visual field develop later. They first emerge prenatally at approximately 37 weeks gestation within layers 4B and 5. After birth (> 40 weeks gestation) the fiber density increases rapidly, showing a uniform plexus of connections at 7 weeks postnatal. The more adult-like patchiness of the projection, however, emerges after 8 weeks postnatal. Long-range horizontal connections within layer 2/3 develop after the connections within layers 4B, 5, and 6. These connections emerge after 16 weeks postnatal, long after cytochrome oxidase blobs have developed, and reach mature from sometime before 15 months of age. Unlike the patchy horizontal projections within layers 4B and 5, which seem to develop through a process of collateral elimination, long-range projections within layer 2/3 are patchy from the outset and seem to develop with greater topographical precision. The finding that intracolumnar connections develop before intercolumnar projections suggests that circuits that process local features of a visual scene develop before circuits necessary to integrate these features into a continuous and coherent neural representation of an image. In addition, the sequential development of horizontal connections within layer 4B before those within layer 2/3 suggests that circuits that may be related to the processing channel for visual motion develop in advance of those that may be more intimately related to the processing of form, color, and precise stereoscopic depth.
Aging↗
A computational model of the vertical anatomical organization of primary visual cortex.
A method for modeling anatomical connectivity for a vertically organized slab of cortical tissue in mammalian primary visual cortex has been developed. The modeled slab covers 500 x 500 microns of cortical surface and extends vertically throughout the full depth of the cortex. The model slab was divided into 6 laminae and neuronal somata were distributed in three dimensions through the slab in accordance with experimentally derived cell densities. Axonal and dendritic arborizations were modeled as line segments. A total of 17 morphological types of neurons were included. Connectivity was established based on proximity between axonal and dendritic arbors. There is good general agreement between the vertical distribution of connections generated by the model and the vertical distribution of synapses observed for cat area 17. In all layers, fewer connections were generated in the model than synapses in cat area 17. This is due, at least in part, to the exclusion of long range intracortical projections and sources of afferent input other than the dorsal lateral geniculate nucleus from the model. The connection scheme described here will be used in conjunction with a physiology model to model vertical signal flow, and will be expanded further to model receptive fields of cortical neurons.
Afferent Pathways↗
A novel algorithm for tracing the interaction of a track with molecular targets--use of Delaunay triangulation.
This paper describes an efficient method for tracing interactions between a radiation track and molecular targets in a cell or nucleus. The method is efficient because it ensures that a minimal subset of interactions in the track needs to be tested for each score. It is most useful for high-energy particles since the number of interactions and range of the tracks increase with particle energy. In this method, the set of interactions, i.e. the track, is considered as a collection of points in three-dimensional space. This set, together with the eight vertices of a bounding box, is discretised as a collection of tetrahedra, each of which satisfies the Delaunay criterion. Because of the geometric properties of these tetrahedra, only those points which are connected to vertices of tetrahedra through which the target passes need be tested for scoring. An efficient algorithm is used to follow the track through the cell or the nucleus. The main benefit of the method is that it eliminates the need to test those interactions which are geometrically distant from the target. In particular, in cases where there are no interactions in the target, very few interactions need to be checked.
Algorithms↗