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PubMed2001

Speed of feedforward and recurrent processing in multilayer networks of integrate-and-fire neurons.

The speed of processing in the visual cortical areas can be fast, with for example the latency of neuronal responses increasing by only approximately 10 ms per area in the ventral visual system sequence V1 to V2 to V4 to inferior temporal visual cortex. This has led to the suggestion that rapid visual processing can only be based on the feedforward connections between cortical areas. To test this idea, we investigated the dynamics of information retrieval in multiple layer networks using a four-stage feedforward network modelled with continuous dynamics with integrate-and-fire neurons, and associative synaptic connections between stages with a synaptic time constant of 10 ms. Through the implementation of continuous dynamics, we found latency differences in information retrieval of only 5 ms per layer when local excitation was absent and processing was purely feedforward. However, information latency differences increased significantly when non-associative local excitation was included. We also found that local recurrent excitation through associatively modified synapses can contribute significantly to processing in as little as 15 ms per layer, including the feedforward and local feedback processing. Moreover, and in contrast to purely feed-forward processing, the contribution of local recurrent feedback was useful and approximately this rapid even when retrieval was made difficult by noise. These findings suggest that cortical information processing can benefit from recurrent circuits when the allowed processing time per cortical area is at least 15 ms long.

Action Potentials↗
PubMed1986

Diffusion of a lymph-carried antigen in the fiber network of the lymph node of the rat.

A lymph-carried antigen is retained preferentially in those areas of the subcapsular sinus of a lymph node overlying the extrafollicular zone of the peripheral cortex. There, it becomes associated with the reticular fibers crossing these particular sinus areas. We wondered whether the antigen thereafter diffuses along the extensions of these fibers which form a peculiar network in the "cortical pathways of migration of circulating lymphocytes" (CPMCL), leading to the different cell populations effecting the immune responses. Fluorescein isothiocyanate (FITC)-conjugated antigens were injected locally into rats sacrificed 0.5-24 h later. The antigens diffused along the fibers of the CPMCL. It is proposed that this diffusion constitutes one mechanism of stimulation of recruited circulating lymphocytes and of orientation of their migration towards the proper effector-cell population.

Animals↗
PubMed2006

Cerebral metabolite differences in adolescents with low birth weight: assessment with in vivo proton MR spectroscopy.

BACKGROUND: Children with very low birth weight (VLBW) have a significantly increased risk of later neurodevelopmental problems, while infants born small for gestational age (SGA) at term are also at some risk of developing neurological impairment. OBJECTIVE: To investigate possible brain metabolite differences in adolescents with VLBW, SGA at term and controls by proton in vivo magnetic resonance spectroscopy (MRS) at 1.5 T. MATERIALS AND METHODS: MR spectra were acquired from volumes localized in the left frontal lobe, containing mainly white matter (54 subjects). Peak areas of N-acetyl aspartate (NAA), choline (Cho) and creatine (Cr) were determined, and the peak area ratio of NAA to Cr, total Cho to Cr, or NAA to Cho calculated. Probabilistic neural network (PNN) analysis was performed utilizing the chemical shift region containing resonances from NAA, Cho and Cr as inputs. RESULTS: No significant difference in the peak area ratios could be found using the Kruskal-Wallis test. By application of PNN, a correct classification of 52 of the 54 adolescents with a sensitivity and specificity exceeding 93% for all groups was achieved. CONCLUSION: Small, yet systematic, differences in brain metabolite distribution among the groups were confirmed by PNN analysis.

Adolescent↗
PubMed2003

Information and communication technology in cardiovascular disease prevention in developing countries: hype and hope. Report of the International Collaboration on Information Use in Cardiovascular Health Promotion in Developing Countries.

Information can be an important tool in promoting a prevention strategy to address the emerging epidemic of cardiovascular disease in developing countries. Advances in information and communication technology offer new promises for global access to information and for global mobilization to prevent and control cardiovascular disease. This is especially true for health professionals, whose needs in areas such as networking, exchange of expertise and access to relevant advances remain unfulfilled. Information technology can also sensitize the lay public to the magnitude of cardiovascular diseases, creating awareness about risk states, and highlighting preventive strategies. Effective application mandates that the technology be relevant to local needs. Cost, feasibility, and relevance of information need to be considered before wide adoption is advocated. Several initiatives, such as ProCOR, Global Cardiovascular Infobase, Heartfile, and the Virtual Congress of Cardiology, have successfully utilized information technology to promote cardiovascular prevention. The experience of these initiatives suggests that, while information technology holds great potential, there are many potential perils, such as the widening global information gap, inequitable access, and irrelevant information. For now, information technology must be viewed as part of a broader strategy, which includes conventional communication media, to address the unmet information needs for cardiovascular prevention globally. Enlightened policies can exploit the energies of the recent information boom for promoting cardiovascular prevention, taking into account the considered limitations.

Cardiovascular Diseases↗
PubMed2003

Cost-effectiveness analysis of recruitment strategies in a community-based intervention study of HIV-infected persons.

This paper describes and evaluates recruitment methods used to reach adults with HIV infection and to enroll eligible candidates in a randomized trial of aerobic exercise. Potential participants residing in the metropolitan Washington DC area were recruited from January 1994 to December 1996. The yield and associated cost of clinic centre site-visit (CSV) recruitment are compared to similar outcomes for community-based (CB) recruitment strategies, which consisted of presentations to local groups, mail/phone canvasses of caregivers, neighbourhood network promotion, public site postings and print media notices. Of 833 HIV infected adults ascertained during the recruitment phase as prospective study candidates, 66.7% were initially contacted during CSV recruitment. The remainder, 33.3% were CB recruits. The percentage of screened candidates who were subsequently enrolled in the study was 13.5% for CSV recruitment and 21% for CB recruitment. Ascertainment and screening costs combined were $158 per CB recruit compared to $232 per CSV recruit. Using multiple recruitment approaches we successfully achieved our enrollment goal of at least 100 volunteers from diverse populations by the end of the planned recruitment period.

Adult↗
PubMed2006

Transfer of interfered motor patterns to self from others.

Previous behavioural and neuroimaging data on humans demonstrated that kinematics and the level of brain activity vary according to whether participants reach towards and grasp a target object presented in isolation or flanked by a distractor object. Here we seek to explore whether a differential activation can be revealed by the mere observation of another person grasping an object in isolation or alongside a distractor. To this end we used event-related functional magnetic resonance imaging to localize neural activity related to action observation that was influenced by the presence of a distractor object. We found that observing a human model reaching-to-grasp a three-dimensional target alongside a distractor elicits a differential level of activation in a network of areas typically involved during action observation: the dorsal sectors of the premotor cortex and the inferior frontal gyrus. Whereas our previous understanding of the human action observation system has been restricted to actions directed to single objects, we provide compelling evidence that areas within this network modulate with respect to the context in which the observed action takes place. This may prove to be a fundamental process for our understanding of how others' actions can be represented at a neural level.

Adult↗
PubMed1992

Isolation, characterization, and localization of cardiac collagen type VI. Associations with other extracellular matrix components.

We have isolated and characterized collagen type VI from murine, canine, and nonhuman primate hearts. In the three species studied, collagen type I was the major collagenous component of the cardiac interstitium (80% of total collagen), whereas collagen type VI represented approximately 5% of total collagen. To define the exact distribution of collagen type VI and its possible interactions with other components of the cardiac extracellular matrix, collagen types I, III, IV, and VI, laminin, and fibronectin were localized in the rat myocardium by immunohistochemistry, using monospecific antibodies. In the rat myocardium, collagen type VI was prevalent in the media and adventitia of muscular arteries, in fine connective tissue septa, in the area surrounding capillaries, and in the delicate endomysium in proximity to myocardial cells. When compared with the immunohistochemical localization of collagen types I, III, and IV, laminin, and fibronectin, the continuity and hierarchical organization of the cardiac extracellular matrix became apparent. The matrix forms a continuous network extending from the pericardium to the endocardium. Furthermore, there is an arborescent hierarchy in the system such that collagen type I is more prevalent in the wider septa, collagen type III being more obvious in medium-sized branches, and fibronectin and collagen type VI prevailing in the terminal (pericellular) aspects of the network. In this pericellular location, fibronectin and collagen type VI, by means of specific interactions, may act as anchor components linking the myocardial cell basement membranes not only to the extracellular matrix but also to the cardiac interstitial cells. This continuity, organization, and coupling of the cardiac extracellular matrix appears well suited to integrate and distribute the physical stress generated by the continuous contraction and relaxation of the myocardium.

Animals↗
PubMedDate not supplied

Outreach, consolidation, and networking: Columbia's approach to successful integration of laboratory services in California.

At the forefront of integrated laboratory services, Columbia Bay Area Healthcare Network's Lab Link provides a unique approach to operating hospital-based laboratories in today's heavily penetrated managed-care environment. Columbia recognizes that a combined strategy of laboratory consolidation, outreach, and networking is essential to compete successfully with commercial reference laboratories for local and statewide contracts. Implementing this model enables hospital laboratories to produce high quality, cost-effective test results while increasing volume and reducing duplication. When hospital laboratories consolidate and network with local and regional laboratories, inpatient and outpatients information is cross-fertilized through a web of information systems. Patients information can then be accessed easily and monitored throughout the continuum of care. The goal of this article is to provide hospital laboratories with a streamlined approach to structuring and delivering services while maintaining a competitive edge in the tumultuous healthcare market. The future of laboratory services within the hospital setting lies in the aggressive use of three elements--consolidation, outreach, and networking--to ensure quality service as well as economic viability.

California↗
PubMedDate not supplied

[Localization of crystallins in Muellerian cells in the grass frog retina].

Cell localization of 23 kDa- and 35 kDa-crystallins in the retina of adult common frogs Rana temporaria L. was studied using indirect immunofluorescence. Intense specific fluorescence of both crystallins was observed all over the retina, in both periphery and central area. It was localized in elongated radially oriented cells, whose bodies were located in the inner nuclear layer. These cells gave many fluorescing processes in the same layer and main processes in the outer nuclear and ganglion layers, one in each. The processes formed a strong network of fibers around the photoreceptor and ganglion cells. Intense fluorescence was also observed in the layer of nerve fibers and adjoining inner limiting membrane. The distribution and morphology of crystalline-containing cells mostly coincides with what is known for the Muller cells of vertebrate eye. The identity of the cells we described and Muller cells was also confirmed using the antiserum to glial fibrillary acidic protein.

Animals↗
PubMed1988

In vivo visualization of callosal pathways: a novel approach to the study of cortical organization.

I describe here the successful visualization of interhemispheric callosal connections in the live mammalian cortex. The development of this method was prompted by the finding that fluorescent tracer labeling of groups of cortical neurons, when done under optimal conditions, is sufficiently intense to be visible even in the whole brain preparation. The new approach could provide a useful tool for enhanced precision in localizing cortical modules in vivo. In a typical experiment, rats had their left cortical hemisphere extensively injected with the fluorescent tract-tracer bisBenzimide (BB). After appropriate survival, the right cortical hemisphere was illuminated with UV light and the fluorescing callosal pattern could be discerned under the network of blood vessels even with the unaided eye. The pattern, although diffuse, was grossly similar to the pattern of callosal connections as seen in flattened, sectioned cortex. Features that could be discerned were: the main callosal band straddling the lateral border of area 17, several rings and bands in extrastriate areas 18a and 18b, and a major band straddling the lateral border of area 3. The vitally visualized callosal pattern was used to guide injections of either wheat germ agglutinin conjugated to HRP (WGA-HRP) or rhodamine-labeled microspheres (RLM) into precisely localized sites in occipital cortex. There were numerous instances of doubly labeled neurons stained both with BB and WGA-HRP or RLM, suggesting that uptake of BB combined with UV exposure did not hinder the ability of stained neurons to take up and transport a second tracer. It is suggested that vital tract tracing be used as a tool for enhanced precision in studies of cortical connectivity.

Animals↗
PubMed2006

Inflammatory processes in the aging mouse brain: participation of dendritic cells and T-cells.

Increased inflammatory activity accompanies normal brain aging. Whereas local glial cell activation, upregulation of cytokines and transcriptional alterations of inflammatory factors are well-documented components of this complex process, it is unclear whether blood-derived leukocytes also contribute to the age-related changes. The present study of normal mouse brain applied single and double immunohistochemistry to reveal for the first time that dendritic cells (DCs) and T-cells are important components of the general increased inflammatory state, which was documented by upregulation of reactive astrocytes and microglia. B-cells and mast cells do not contribute to this inflammatory response. Dendritic cells and T-cells appeared at about 12 months of age and their number increased further during aging. In 24-month-old animals a dense network of DCs interspersed with T-cells pervaded brain areas where substantial histopathological changes and a volumetric decrease have been reported. All CD11c(+)-DCs displayed the typical dendritic shape and expressed the myeloid specific integrin CD11b. Some of the DCs were also CD205- or MIDC8-immunoreactive and expressed the cathepsins S and X. The emergence and prolonged presence of leukocytes might indicate a crucial role of these cells in local, age-related immune responses in the brain.

Aging↗
PubMed2003

Impaired thalamocortical connectivity in humans during general-anesthetic-induced unconsciousness.

Whereas converging lines of evidence suggest that anesthetic-induced unconsciousness may result from disruption of functional interactions within neural networks involving the thalamus and cerebral cortex, the effects anesthetics have on human thalamocortical connectivity remain unexamined with current neuroimaging techniques. To address this issue we retrospectively analyzed positron emission tomography data from 11 volunteers scanned for regional cerebral glucose utilization (rCMRglu) when awake and again during isoflurane- (n = 6) or halothane- (n = 5) induced unconsciousness using statistical parametric mapping (SPM99) and structural equation modeling. A main effect analysis, contrasting awake and unconscious metabolic activity, localized a discrete region of the left va/vl thalamus whose relative rCMRglu activity was significantly suppressed (P < 0.05, corrected) during the unconscious state. To identify brain regions whose functional connectivity with this region of the thalamus was impaired during the unconscious state, a psychophysiological interaction analysis was performed. This analysis revealed effects predominantly in topographically related areas of the primary motor and supplementary motor association cortices. Structural equation modeling of a neuroanatomical network encompassing these empirically identified regions revealed significant state-related changes in effective connectivity (chi(2)diff (6)-15.88; P < 0.05) which primarily involved impairment of thalamocortical and corticocortical projections during the unconscious state. These findings support the hypothesis that a mechanistic component underlying general-anesthetic-induced unconsciousness involves disruption of functional interactions within thalamocortical neural networks.

Anesthesia, General↗
PubMed2004

Electrical neuroimaging based on biophysical constraints.

This paper proposes and implements biophysical constraints to select a unique solution to the bioelectromagnetic inverse problem. It first shows that the brain's electric fields and potentials are predominantly due to ohmic currents. This serves to reformulate the inverse problem in terms of a restricted source model permitting noninvasive estimations of Local Field Potentials (LFPs) in depth from scalp-recorded data. Uniqueness in the solution is achieved by a physically derived regularization strategy that imposes a spatial structure on the solution based upon the physical laws that describe electromagnetic fields in biological media. The regularization strategy and the source model emulate the properties of brain activity's actual generators. This added information is independent of both the recorded data and head model and suffices for obtaining a unique solution compatible with and aimed at analyzing experimental data. The inverse solution's features are evaluated with event-related potentials (ERPs) from a healthy subject performing a visuo-motor task. Two aspects are addressed: the concordance between available neurophysiological evidence and inverse solution results, and the functional localization provided by fMRI data from the same subject under identical experimental conditions. The localization results are spatially and temporally concordant with experimental evidence, and the areas detected as functionally activated in both imaging modalities are similar, providing indices of localization accuracy. We conclude that biophysically driven inverse solutions offer a novel and reliable possibility for studying brain function with the temporal resolution required to advance our understanding of the brain's functional networks.

Biophysics↗
PubMed2005

Rhythmic brain activity at rest from rolandic areas in acute mono-hemispheric stroke: a magnetoencephalographic study.

In order to deepen our knowledge of the brain's ability to react to a cerebral insult, it is fundamental to obtain a "snapshot" of the acute phase, both for understanding the neural condition immediately after the insult and as a starting point for follow-up and clinical outcome prognosis. The characteristics of the brain's spontaneous neuronal activity in perirolandic cortical areas were investigated in 32 patients who had a stroke in the middle cerebral artery (MCA) territory of one hemisphere in the previous 10 days. Magnetic fields from both left and right rolandic areas were recorded at rest with open eyes. Total and band power properties, the individual alpha frequency (IAF) and the spectral entropy were analyzed and compared with a sex-age matched control group. In agreement with electroencephalographic literature, low frequency absolute powers were higher and high frequency were lower in the affected (AH) than in the unaffected hemisphere (UH), and also their values in both hemispheres differed from control values. An IAF reduction was found in AH with respect to UH. As new findings, the total power was higher in AH than in UH, after excluding 4 right-damaged patients with cortico-subcortical lesions, who showed a completely disorganized spectral pattern. Spectral entropy was lower in AH than in UH. Clinical severity correlated with the AH decrease of gamma band power, IAF and spectral entropy. Larger lesions were associated to worse clinical pictures and MEG alterations. A lesion affecting the MCA territory of one hemisphere induces a perilesional increase of the low-frequency rhythms' spectral power within the AH rolandic areas; the same effect was present also in the UH, indicating interhemispheric diaschisis. In the AH, results showed an increase of the total power and a reduction of the spectral entropy, suggesting a higher synchrony of local neuronal activity, a reduction of the intra-cortical inhibitory networks efficiency and an increase of neuronal excitability. Direct correlation linked gamma band activity preservation and less severe clinical status. Dependence of the clinical picture, and associated spectral alterations, on the lesion volume and not on the lesion level, suggests a diffuse neuronal impairment, rather than a selective structures damage, contributing to neurological status in the acute phase of stroke.

Adult↗
PubMed2002

The use of contracts in the management of infectious disease related risk in the NHS internal market.

The paper reports a unique study of contracting for infectious disease control in the English National Health Service internal market. New-institutional economic and socio-legal theories are used to predict that it will not be possible to make contracts for the control of infectious disease which are complete with respect to either the allocation of financial risk or the specification of quality standards. Socio-legal theory predicts that in some circumstances informal relationships (known as networks or relational contracts) can evolve to compensate for some of the deficiencies of incomplete contracts. NHS policy makers are shown to have expected and continue to expect that contracts can be complete. The study comprised five in-depth case studies of contracting in different local areas in England and a national survey of all infection control professionals. The results confirm the theoretical predictions. Contracts were not complete, and some of the elements of relational contracts were present. These elements did not, however, fully compensate for the lack of clear accountability caused by contractual incompleteness.

Communicable Disease Control↗
PubMedDate not supplied

[Intersectorial activities for traffic accident prevention].

We describe priority issues and some of the results obtained from the implementation of the Prevention and Reduction of Traffic Accident Injuries program in a health area. Since 1999 the public health center has made a priority of identifying and recruiting partners from other sectors (the local police association and the local education authority), increasing its capacity for working together, and setting up an intersectorial working group. Teaching activities and meetings were held. A network of people was created from 17 of a total of 39 town halls that participate in activities supported by the intersectorial group. Ten are involved in educational activities and a further seven focus on ensuring compliance with the law. The intersectorial group promoted their visibility through the local media. These activities are not aimed at reducing injuries from road traffic accidents, but rather at creating an action framework through which all the sectors involved can be mobilized. The aim is to strengthen commitment among political, technical and civil sectors by focussing on social values of respect for a healthier life.

Accidents, Traffic↗
PubMed1995

Segmenting textures using cells with adaptive receptive fields.

Textural segmentation plays an important role in the figure-ground discrimination process. Evidence from neuroscience and psychophysics suggests that the segregation of texture patterns composed of oriented line segments is strongly influenced by the orientation contrast between the patterns (Nothdurft, Vision Res. 31, 1073-1078, 1991). In contrast to models available in the literature, this paper presents a neural network architecture for textural segmentation that can adaptively delimit the boundaries of uniformly textured regions. Cells with adaptive receptive fields encode uniformly textured regions by diffusively interpolating the estimates of feature orientations across the image. Orientation contrast boundaries are detected at gradients across the interpolated regions to produce the final segmentation. Consistent with neurophysiological data from simple and complex cells sensitive to static and moving textural patterns (Hammond and MacKay, Exp. Brain Res. 30, 275-296, 1977), the present model suggests that preattentive textural segregation can be performed by early visual processes localized to areas V1, V2, and perhaps V3 or V5. The computational results further support the idea that textural segmentation should not be thought of as a 'static' process, but as a system that employs cells with context-dependent response characteristics (Gilbert and Wiesel, Vision Res. 30, 1689-1701, 1990), here modeled as adaptive receptive fields.

Adaptation, Ocular↗
PubMed1993

Analysis of the immunohistochemical localization of collagen type III and V for the time-estimation of human skin wounds.

Collagen type III and V were visualized immunohistochemically in 79 surgically treated human skin wounds with a wound age between 8 h and 2.5 months. Network-like structures positively staining for collagen type III and associated with fibroblastic cells in the wound area were first detectable in a 2.5-day-old skin lesion and occurred regularly in wounds more than 5 days old. Collagen type V appeared first in the wound area after about 3 days, slightly later than collagen type III, and was detectable regularly in wounds with a survival time of 6 days or more. The immunohistochemical detection of collagen type III or type V thus indicates a wound age of at least 2-3 days. The lack of a positive reaction in a sufficient number of specimens indicates a wound age of less than 6 days. Even though both collagen types could also be detected in older wounds (wound age 2.5 months), further information for the time-estimation of older skin wounds cannot be given due to the observation that the time period during which reparative processes can be observed depends on the extent of the wound area.

Collagen↗