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PubMed2003

Scaling laws for the movement of people between locations in a large city.

Large scale simulations of the movements of people in a "virtual" city and their analyses are used to generate insights into understanding the dynamic processes that depend on the interactions between people. Models, based on these interactions, can be used in optimizing traffic flow, slowing the spread of infectious diseases, or predicting the change in cell phone usage in a disaster. We analyzed cumulative and aggregated data generated from the simulated movements of 1.6 x 10(6) individuals in a computer (pseudo-agent-based) model during a typical day in Portland, Oregon. This city is mapped into a graph with 181,206 nodes representing physical locations such as buildings. Connecting edges model individual's flow between nodes. Edge weights are constructed from the daily traffic of individuals moving between locations. The number of edges leaving a node (out-degree), the edge weights (out-traffic), and the edge weights per location (total out-traffic) are fitted well by power-law distributions. The power-law distributions also fit subgraphs based on work, school, and social/recreational activities. The resulting weighted graph is a "small world" and has scaling laws consistent with an underlying hierarchical structure. We also explore the time evolution of the largest connected component and the distribution of the component sizes. We observe a strong linear correlation between the out-degree and total out-traffic distributions and significant levels of clustering. We discuss how these network features can be used to characterize social networks and their relationship to dynamic processes.

Community Networks↗
PubMed2006

Motion analysis of articulated objects from monocular images.

This paper presents a new method of motion analysis of articulated objects from feature point correspondences over monocular perspective images without imposing any constraints on motion. An articulated object is modeled as a kinematic chain consisting of joints and links, and its 3D joint positions are estimated within a scale factor using the connection relationship of two links over two or three images. Then, twists and exponential maps are employed to represent the motion of each link, including the general motion of the base link and the rotation of other links around their joints. Finally, constraints from image point correspondences, which are similar to that of the essential matrix in rigid motion, are developed to estimate the motion. In the algorithm, the characteristic of articulated motion, i.e., motion correlation among links, is applied to decrease the complexity of the problem and improve the robustness. A point pattern matching algorithm for articulated objects is also discussed in this paper. Simulations and experiments on real images show the correctness and efficiency of the algorithms.

Algorithms↗
PubMed1999

Congestive heart failure induced by recipient atrial tachycardia conducted to the donor atrium after orthotopic heart transplantation: complete regression after successful radiofrequency ablation.

We describe the case of a 30-year-old female patient who developed an interatrial tachycardia from the recipient to the donor atrium associated with signs of congestive heart failure 5 years after orthotopic heart transplantation. The patient underwent catheter mapping followed by successful radiofrequency (RF) ablation at the site of the presumed electrical connection between the recipient and the donor atria, through the interatrial surgical suture line, with stable recovery of sinus rhythm and disappearance of signs of left ventricular dysfunction. RF catheter ablation is confirmed to be feasible and safe in the treatment of heart transplant patients even in the presence of rare forms of arrhythmias, thus offering a cure for tachycardia to these patients.

Adult↗
PubMed1991

Reorganization of somatosensory area 3b representations in adult owl monkeys after digital syndactyly.

1. These experiments were designed to test the hypothesis that temporally correlated afferent input activity plays a lifelong role in the establishment and modification of receptive fields (RFs) and representational topographies in the primary somatosensory cortex of adult monkeys. They were based in part on the finding that adjacent digits of the hand are represented discontinuously in area 3b of the adult owl monkey. If cortical receptive fields and the details of cortical topographic representations are shaped by the weights of the temporal correlations among afferent inputs, then representational discontinuities between digits would be expected to arise because inputs from the skin surfaces of adjacent digits are largely independent in the critical time domain. 2. In the present experiments, the skin of adjacent digits 3 and 4 of the monkey hand was surgically connected to create an artificial syndactyly, or webbed-finger condition. Highly detailed microelectrode maps of the cortical representation of the syndactyl digits were obtained 3-7.5 mo later. This experimental manipulation greatly increased the amount of simultaneous or nearly simultaneous input from the normally separated, now fused, surfaces of adjacent fingers. 3. Cortical maps of the representations of finger surfaces were highly modified from the normal after a several-month-long period of digital fusion. Specifically, the normal discontinuity between the cortical representations of adjacent fingers was abolished. Within a wide cortical zone, RFs were defined that extended across the line of syndactyly onto the surgically joined skin of both fused digits. The representational topography of the fused digits was similar to any normal single digit and was characterized by a continuous progression of partially overlapping RFs. 4. Control observations revealed that these reorganizational changes cannot be accounted for by any changes in cutaneous innervation induced by the surgery. They must arise from representational changes in the central somatosensory system. 5. These findings reveal that cortical maps can be altered in detail in adult monkeys by modifying the distributed temporal structure of afferent inputs. They support the longstanding hypothesis that the temporal coincidence of inputs plays a role in the grouping of input subsets into specific cortical RFs and, consequently, in the shaping of selected effective cortical inputs and representational topographies throughout life.

Animals↗
PubMed2006

fMRI of lexical-semantic priming in a chronic schizophrenia patient.

A neuropsychological hallmark of schizophrenia is a breakdown in semantic association networks that often impacts language and formal thought. Although computational models simulating this breakdown exist, studies have yet to investigate this phenomena using functional MRI (fMRI) coupled with an auditory lexical-decision semantic priming paradigm. Thus, this serves to functionally map brain activation to word pairs that differed with respect to a concept called "connectivity" in a patient with schizophrenia and a demographically matched control adult. Analyses revealed a striking difference with respect to the expected stepwise modulation of activation, with the control participant showing significantly greater areas of modulation than the participant with schizophrenia in regions classically implicated in language. Although the results are tentative because of the nature of this investigation (single-case study), they further support the characterization of schizophrenia as a breakdown in lexical-semantic association networks and represent one of the first fMRI studies of semantic priming in schizophrenia informed by a computer model.

Brain↗
PubMed2003

Properties of a temporal population code.

The temporal patterning of neuronal activity may play a substantial role in the representation of sensory stimuli. One particular hypothesis suggests that visual stimuli are represented by the temporal evolution of the instantaneous firing rate averaged over a whole population of neurons. Using an implementation in a cortical type network with lateral interactions, we could previously show that this scheme can be successfully applied to a pattern recognition task. Here, we use a large set of artificially generated stimuli to investigate the coding properties of the network in detail. The temporal population code generated by the network is intrinsically invariant to stimulus translations. We show that the encoding is invariant to small deformations of the stimuli and robust with respect to static and dynamic variations in synaptic strength of the lateral connections in the network. Furthermore, we present several measures which indicate that the encoding maps the stimuli into a high-dimensional space. These results show that a temporal population code is a promising approach for the encoding of relevant stimulus properties while simultaneously discarding the irrelevant information.

Animals↗
PubMed2006

Spatial modeling in ecology: the flexibility of eigenfunction spatial analyses.

Recently, analytical approaches based on the eigenfunctions of spatial configuration matrices have been proposed in order to consider explicitly spatial predictors. The present study demonstrates the usefulness of eigenfunctions in spatial modeling applied to ecological problems and shows equivalencies of and differences between the two current implementations of this methodology. The two approaches in this category are the distance-based (DB) eigenvector maps proposed by P. Legendre and his colleagues, and spatial filtering based upon geographic connectivity matrices (i.e., topology-based; CB) developed by D. A. Griffith and his colleagues. In both cases, the goal is to create spatial predictors that can be easily incorporated into conventional regression models. One important advantage of these two approaches over any other spatial approach is that they provide a flexible tool that allows the full range of general and generalized linear modeling theory to be applied to ecological and geographical problems in the presence of nonzero spatial autocorrelation.

Animals↗
PubMed2006

Accuracy of an oscillometric blood pressure monitor during phenylephrine-induced hypertension in dogs.

OBJECTIVE: To examine the agreement between direct arterial blood pressure measurements obtained from 2 arteries and indirect blood pressure measurements obtained with an oscillometric blood pressure monitor (OBPM) during normotension and phenylephrine-induced hypertension in dogs. ANIMALS: 16 male Beagles. PROCEDURES: In anesthetized dogs, arterial catheters were placed in the lingual and dorsal pedal arteries for measurement of arterial blood pressure. A blood pressure cuff was placed on either the dog's fore- or hind limb and connected to an OBPM. Systolic, diastolic, and mean arterial blood pressures (SAP, DAP, and MAP, respectively) were recorded from both arteries and the OBPM every 5 minutes for 30 minutes (baseline), during a 30-minute period in which dogs received a phenylephrine infusion IV to induce hypertension, and for 30 minutes after discontinuation of the infusion. Mean differences in blood pressure values and confidence intervals were calculated to compare the indirect and direct measurement techniques. RESULTS: In dogs, oscillometry underestimated SAP during normotension, and the difference between oscillometric and direct measurements increased during hypertension. Oscillometry underestimated DAP, but the difference between oscillometric and direct measurements decreased during hypertension. There was close agreement among techniques for MAP determinations. Biases between direct measurements and OPBM blood pressure values measured from dogs' forelimbs or hind limbs were not significantly different. CONCLUSIONS AND CLINICAL RELEVANCE: In normotensive dogs, oscillometric measurements of MAP and SAP agreed more closely with direct arterial pressure measurements than oscillometric estimates of DAP. Oscillometric measurement of MAP was accurate during both normotension and hypertension in dogs.

Animals↗
PubMed2002

Differential metabolic activity in the striosome and matrix compartments of the rat striatum during natural behaviors.

The striosome and matrix compartments of the striatum are clearly identified by their neurochemical expression patterns and anatomical connections. To determine whether these compartments are distinguishable functionally, we used [14C]deoxyglucose metabolic mapping in the rat and tested whether neutral behavioral states (free movement, gentle restraint, and focal tactile stimulation under gentle restraint) were associated with regions of high metabolic activity in the matrix, in striosomes, or in both. We identified metabolic peaks in the striatum by means of image analysis, striosome-matrix boundaries by [3H]naloxone binding, and primary somatosensory corticostriatal input clusters by injections of anterograde tracer into electrophysiologically identified sites in SI. Peak metabolic activity was primarily confined to the matrix compartment under each behavioral condition. These findings show that during relatively neutral behavioral conditions the balance of activity between the two compartments favors the matrix and suggest that this balance is present in the striatum as part of normal behavior and processing of afferent activity.

Animals↗
PubMed2002

Molecular linkage map of allotetraploid cotton ( Gossypium hirsutum L. x Gossypium barbadense L.) with a haploid population.

In the present study, a haploid population from the cross of the two cultivated allotetraploid cottons, Gossypium hirsutum L. and Gossypium barbadense L., was developed by means of Vsg, a virescently marked semigamous line of Sea island cotton, and some target haploids were successfully doubled with colchicine. A molecular linkage map was constructed with 58 doubled and haploid plants. Among the total of 624 marker loci (510 SSRs and 114 RAPDs), 489 loci were assembled into 43 linkage groups and covered 3,314.5 centi-Morgans (cM). Using the monosomic and telodisomic genetic stocks, the linkage groups of the present map were associated with chromosomes of the allotetraploid genome, and some of the unassociated groups were connected to corresponding A or D subgenomes. Through the analysis of the assignment of the duplicated SSR loci in the chromosomes or the linkage groups, ten pairs of possible homoeologous chromosome (or linkage group) regions were identified. Among them, the pairs of Chrs. 1 and 15, Chrs. 4 and 22, and Chrs. 10 and 20 had already been determined as homoeologous by classical genetic and cytogenetic research, and the pair of Chrs. 9 and 23 had also been identified by the ISH method of molecular cytogenetics. But, from present research, it was assumed that Chrs. 5 and 18 might be a new pair of homoeologous chromosomes of the allotetraploid cotton genome detected by molecular mapping of the cotton genome.

Journal Article↗
PubMed2003

Effects of heart isolation, voltage-sensitive dye, and electromechanical uncoupling agents on ventricular fibrillation.

We tested whether the interventions typically required for optical mapping affect activation patterns during ventricular fibrillation (VF). A 21 x 24 unipolar electrode array (1.5 mm spacing) was sutured to the left ventricular epicardium of 16 anesthetized pigs, and four episodes of electrically induced VF (30-s duration) were recorded. The hearts were then rapidly excised and connected to a Langendorff perfusion apparatus. Four of the hearts were controls, in which 24 additional VF episodes were then mapped. In the remaining 12 hearts, four VF episodes were mapped after isolation, four more episodes were mapped after exposure to the voltage-sensitive dye di-4-ANEPPS, and six more episodes were mapped after exposure to the electromechanical uncoupling agents diacetyl monoxime (DAM; 20 mmol/l, n = 6) or cytochalasin D (CytoD; 10 micromol/l, n = 6). VF episodes were separated by 4 min. VF activation patterns were quantified using custom pattern analysis algorithms. From comparisons with time-corrected control data, all interventions significantly changed VF patterns. Most changes were broadly consistent with slowing and regularization due to loss of excitability. Heart isolation had the largest effect on VF patterns, followed by CytoD, DAM, and dye.

Animals↗
PubMed2000

[Thalamo-cortical system and consciousness].

After reviewing the concept of the specific and non specific thalamo-cortical systems, the connectivity of the relay and intralaminar nuclei is analyzed as well as the recent data concerning the chemical identity of thalamic neurones, the concept and distribution of "matrix" and "core" neurones and its functional role. The intrinsic electrical properties of thalamic neurones, its mode of discharge--depending of the membrane potential level--and its functional significance in the context of the brain's global activity are discussed. Of special interest are the studies on the effects of lesion of the relay and intralaminar nuclei as well as its repercussion in the interpretation of the sensory perception. After intralaminar nuclei lesion the individual is not aware of the nformation conveyed through the specific channels. It follows a discussion on the importance of the temporal and spatial mapping in the elaboration of perception and cognition. Due to the intrinsic electrical properties and the connectivity of thalamic neurones two groups of corticothalamic loops are generated, which resonate at a frequency of 40 Hz. The specific thalamo-cortical loops give the content of cognition and the no specific loop, the temporal binding required for the unity of the cognitive experience. Consciousness is then, a product of the resonant thalamo-cortical activity, and the dialogue between the thalamus and cortex, the process that generates subjectivity, the unique experience we all recognized as the existence of the "self".

Cerebral Cortex↗
PubMed1997

Tenascin-X deficiency is associated with Ehlers-Danlos syndrome.

The tenascins are a family of large extracellular matrix proteins with at least three members: tenascin-X (TNX), tenascin-C (TNC, or cytotactin) and tenascin-R (TN-R, or restrictin). Although the tenascins have been implicated in a number of important cellular processes, no function has been clearly established for any tenascin. We describe a new contiguous-gene syndrome, involving the CYP21B and TNX genes, that results in 21-hydroxylase deficiency and a connective-tissue disorder consisting of skin and joint hyperextensibility, vascular fragility and poor wound healing. The connective tissue findings are typical of the Ehlers-Danlos syndrome (EDS). The abundant expression of TNX in connective tissues is consistent with a role in EDS, and our patient's skin fibroblasts do not synthesize TNX protein in vitro or in vivo. His paternal allele carries a novel deletion arising from recombination between TNX and its partial duplicate gene, XA, which precludes TNX synthesis. Absence of TNX mRNA and protein in the proband, mapping of the TNX gene and HLA typing of this family suggest recessive inheritance of TNX deficiency and connective-tissue disease. Although the precise role of TNX in the pathogenesis of EDS is uncertain, this patient's findings suggest a unique and essential role for TNX in connective-tissue structure and function.

Adult↗
PubMed1994

Thermoregulatory fluctuations in heart rate and blood pressure in humans: effect of cooling and parasympathetic blockade.

The spontaneous fluctuations in acral skin blood flow, mean blood pressure (MAP), and heart rate (HR) were studied in 9 healthy supine volunteers in a thermoneutral and in a cool environment, and after parasympathetic blockade by atropine. In skin areas with a high density of arteriovenous anastomoses (AVAs), there were large, spontaneous fluctuations in blood flow in a thermoneutral environment. The fluctuations were nearly abolished in a cool environment, while they seemed unaffected by atropine administration. Power spectral analysis demonstrated a reduction in HR and MAP variability in the low- and mid-frequency (LF) (< 0.15 Hz) band after cooling, and a prominent reduction in HR variability in both the LF and the high-frequency (HF) (< 0.15 Hz) band after atropine administration. A sudden drop in skin vascular conductance was accompanied by diphasic HR changes and an increase in MAP. After atropine administration, the initial HR acceleration was delayed and reduced in magnitude. The secondary HR deceleration, which probably represents baroreceptor modulation, was abolished. Atropine administration caused a delayed, but augmented increase in MAP, which was probably related to the loss of baroreceptor control of HR. The presence of an autonomic rhythm, consisting of sympathetic vasoconstrictor impulses to skin AVAs, connected with reciprocal sympathetic and vagal impulses to the heart, is indicated. The HR changes were mainly determined by vagal activity. The rhythmic changes in skin blood flow, HR and MAP were suppressed in a cool environment.

Adult↗
PubMed1994

The HELIOS Medical Connection Services.

This paper presents the design and implementation of the HELIOS software component that deals with integration of medical applications in health information networks. The problem of interoperability between health information systems based on different data exchange syntaxes is first discussed. A meta-model, relying on CEN TC251 recommendations, is then presented as a possible solution to this problem and a message description language including these recommendations is proposed. Using this meta-model, the Medical Connection Services that comprises a generic message processing automaton, a resource manager and a mapper is able either to interpret messages expressed in a given syntax (e.g., EDIFACT, ASTM) and map them to the application objects or to automate the translation of the messages in another syntax. Special focus is given on the position of the Medical Connection Services within the HELIOS integration strategy (i.e., through data, presentation and communication). The problem of semantic heterogeneity is then discussed.

Computer Communication Networks↗
PubMed1981

Principles of organization of a cerebro-cerebellar circuit. Micromapping the projections from cerebral (SI) to cerebellar (granule cell layer) tactile areas of rats.

We defined spatial patterns of organization of projections from somatosensory cerebral cortex (SI) to the somatosensory cerebellar cortex of anesthetized albino rats using microelectrode (stimulation and recording) micromapping methods and low-threshold cutaneous (tactile) stimulation. Two sampling strategies were used: (1) a single cerebral SI locus in layers V-VI was stimulated electrically, while a responding region of the cerebellar granule cell (GC) layer was systematically mapped with a recording electrode; (2) the SI stimulating electrode was used as the mapping electrode while the cerebellar GC electrode remain fixed. We found highly specific patterns of connections between somatotopically organized SI cortex and the somatotopically fractured tactile cerebellar cortex. Using threshold stimulating currents in SI, the projections from small populations of neural elements were found to be highly restricted, terminating within the confines of only those tactile cerebellar hemispheric locations having the same receptive fields (RFs). These SI-GC projections conform to the patchy mosaic pattern of organization previously shown for peripheral tactile projections. SI projections to GC patches were either contralateral or ipsilateral, depending on the laterality of the peripheral projections to that patch. Each SI focus projected to only a portion of a patch; projections from several adjacent SI loci overlapped serially within a patch. As with the peripherally evoked GC layer responses, SI-evoked GC responses were organized in a columnar fashion and were maximal at middle levels of the GC layer; SI-GC latencies were 5-8 ms. These data reveal that this tactile-related cerebro-cerebellar circuit exhibits precisely organized patterns of projection.

Animals↗
PubMed2001

Calibrated single-plunge bipolar electrode array for mapping myocardial vector fields in three dimensions during high-voltage transthoracic defibrillation.

Mapping of the myocardial scalar electric potential during defibrillation is normally performed with unipolar electrodes connected to voltage dividers and a global potential reference. Unfortunately, vector potential gradients that are calculated from these data tend to exhibit a high sensitivity to measurement errors. This paper presents a calibrated single-plunge bipolar electrode array (EA) that avoids the error sensitivity of unipolar electrodes. The EA is triaxial, uses a local potential reference, and simultaneously measures all three components of the myocardial electric field vector. An electrode spacing of approximately 500 microm allows the EA to be direct-coupled to high-input-impedance, isolated, differential amplifiers and eliminates the need for voltage dividers. Calibration is performed with an electrolytic tank in which an accurately measured, uniform electric field is produced. For each EA, unique calibration matrices are determined which transform potential difference readings from the EA to orthogonal components of the electric field vector. Elements of the matrices are evaluated by least squares multiple regression analysis of data recorded during rotation of the electric field. The design of the electrolytic tank and electrode holder allows the electric field vector to be rotated globally with respect to the electrode axes. The calibration technique corrects for both field perturbation by the plunge electrode body and deviations from orthogonality of the electrode axes. A unique feature of this technique is that it eliminates the need for mechanical measurement of the electrode spacing. During calibration, only angular settings and voltages are recorded. For this study, ten EAs were calibrated and their root-mean-square (rms) errors evaluated. The mean of the vector magnitude rms errors over the set of ten EAs was 0.40% and the standard deviation 0.07%. Calibrated EAs were also tested for multisite mapping in four dogs during high-voltage transthoracic shocks.

Animals↗
PubMed1983

Anatomical evidence for segregated focal groupings of efferent cells and their terminal ramifications in the cerebellothalamic pathway of the monkey.

Patterns of termination of the cerebellothalamic pathway were investigated using anterograde tracing techniques. The thalamic projections from each of the deep cerebellar nuclei are topographically organized in two and possibly in three dimensions. First, the caudo-rostral cerebellar nuclear dimension is mapped onto the mediolateral dimension within the cell-sparse ventral lateral thalamic region (VPLo, VLc, VLps, and nucleus X). By correlating this topographic ordering with the previously established lamellar organization of the cell-sparse thalamic region a somatotopy is inferred within the deep cerebellar nuclei, with caudal body parts represented anteriorly and rostral body parts represented posteriorly in each nucleus. A second topography consists of the mapping of the mediolateral dimension of the dentate and interpositus nuclei onto the ventrodorsal dimension of the lamellae in the thalamus. Since the thalamic connections with motor cortex predict a somatotopic organization with distal body parts ventral and axial parts dorsal in thalamus, each cerebellar nucleus should, therefore, represent axial body parts laterally and distal parts medially. A third mapping dimension is shown for the dentatothalamic projection: dorsal parts of the dentate nucleus project posteriorly within the cell-sparse thalamic region, and ventral parts project anteriorly. The significance of this as regards representation of the body is not known. Subsidiary foci of terminations within the cell-sparse thalamic region are visible following tritiated amino acid injections into each of the deep cerebellar nuclei. Following dentate injections these foci appear as anteroposteriorly elongated, rod-like aggregations of terminations which are similar to the rod-like aggregations of thalamocortical relay cells which have been demonstrated following focal injections of horseradish peroxidase into the motor cortex. The interpositothalamic and the fastigiothalamic terminations are elongated and appear as focal clusters in all planes of section. The interpositothalamic clusters are distributed within posterodorsally curving planar sheets. An anterograde double labeling technique, using a combination of the autoradiographic technique with the axonal degeneration technique, was used to investigate the interrelations of the terminations from different nuclei and from different parts of the same nucleus. Rods from different parts of the dentate nucleus terminate independently of one another. Dentatothalamic rods and interpositothalamic clusters, though interdigitating within the same thalamic region, do not overlap. This topographic and modular organization of the cerebellothalamic pathway suggests that the cerebellar input may reflect both the somatotopic and the columnar organization of the motor cortex.

Animals↗