Rate of neuronal fallout in a transsynaptic cerebellar model

PURPOSE: A retrospective study was undertaken of the late adverse reactions following the injection of contrast media. The purpose was to determine whether there was a difference between non-ionic monomeric (iohexol) and non-ionic dimeric (iodixanol) contrast media in the reactions produced. MATERIAL AND METHODS: A total of 3,408 patients were sent a written questionnaire in which they were asked to confirm or deny any subjective discomfort or adverse event during a period of one hour to one week after a previous radiological examination with contrast medium. Patients who had undergone angiography (i.v. or i.a. injection) and CT (i.v. injection) were included. Objective signs of an allergy-like reaction were listed and the patients were asked to subjectively quantify any consequent discomfort. RESULTS: The compliance rate was 84%. Of the 3075 injections finally included in the study, 133 (4.3%) had resulted in contrast-medium-related adverse reactions of which 72 (2.3%) were immediate and 61 (2%) were late. Iohexol induced late reactions in 14/851 (1.7%) cases, and iodixanol in 24/1218 (2.0%) cases following i.v. injection and in 23/1006 (2.3%) cases following i.a. injection. The differences were not significant. There were no differences between the two contrast media in the subjective rating of discomfort except that the patients who had received iodixanol also had the highest individual-intensity score. No patient had been hospitalized owing to an adverse reaction and all reactions had been regarded as mild or moderate. CONCLUSION: The number of late adverse reactions was low. There was no difference in the frequency of the late adverse reactions following i.v. injection between iodixanol and iohexol. There was also no difference in the reactions between the i.a. and i.v. injections of iodixanol.     

A neuronal model of a global workspace in effortful cognitive tasks

A minimal hypothesis is proposed concerning the brain processes underlying effortful tasks. It distinguishes two main computational spaces: a unique global workspace composed of distributed and heavily interconnected neurons with long-range axons, and a set of specialized and modular perceptual, motor, memory, evaluative, and attentional processors. Workspace neurons are mobilized in effortful tasks for which the specialized processors do not suffice. They selectively mobilize or suppress, through descending connections, the contribution of specific processor neurons. In the course of task performance, workspace neurons become spontaneously coactivated, forming discrete though variable spatio-temporal patterns subject to modulation by vigilance signals and to selection by reward signals. A computer simulation of the Stroop task shows workspace activation to increase during acquisition of a novel task, effortful execution, and after errors. We outline predictions for spatio-temporal activation patterns during brain imaging, particularly about the contribution of dorsolateral prefrontal cortex and anterior cingulate to the workspace.     

Emergent spindle oscillations and intermittent burst firing in a thalamic model: specific neuronal mechanisms

The rhythmogenesis of 10-Hz sleep spindles is studied in a large-scale thalamic network model with two cell populations: the excitatory thalamocortical (TC) relay neurons and the inhibitory nucleus reticularis thalami (RE) neurons. Spindle-like bursting oscillations emerge naturally from reciprocal interactions between TC and RE neurons. We find that the network oscillations can be synchronized coherently, even though the RE-TC connections are random and sparse, and even though individual neurons fire rebound bursts intermittently in time. When the fast gamma-aminobutyrate type A synaptic inhibition is blocked, synchronous slow oscillations resembling absence seizures are observed. Near-maximal network synchrony is established with even modest convergence in the RE-to-TC projection (as few as 5-10 RE inputs per TC cell suffice). The hyperpolarization-activated cation current (Ih) is found to provide a cellular basis for the intermittency of rebound bursting that is commonly observed in TC neurons during spindles. Such synchronous oscillations with intermittency can be maintained only with a significant degree of convergence for the TC-to-RE projection.     

Effects of synaptic noise on a neuronal pool model with strong excitatory drive and recurrent inhibition

A model originally proposed by Akazawa and Kato (1990) for the spinal cord was adopted as prototypical of a neuronal pool with strong excitatory drive and strong recurrent inhibition. Our simulations of the model have shown that a strong synchronization occurs between the spike trains in the neuronal pool. This happens because the proposed model has a single and strong excitatory drive on the neuronal pool. However, usually a multitude of other randomly occurring synaptic inputs impinge on the neuronal pool and therefore a new investigation was carried out to study the effects of synaptic noise on the network behavior. The synaptic noise decreased the degree of synchronization of the neuronal spike trains but on the other hand caused an unexpected decrease in the mean firing rate of the neuronal pool. A detailed analysis indicated that this phenomenon is due to a combination of two mechanisms: a saturation of the feedback inhibition and a decrease of the synchronization in the neuronal pool with synaptic noise. The synaptic noise caused a more frequent activation of the saturated recurrent inhibitory feedback loop along time, thereby increasing the inhibitory effect on the neuronal pool.     

Behavioral constraints in the development of neuronal properties: a cortical model embedded in a real-world device

The ability of organisms to categorize diverse and often novel stimuli depends on ongoing interactions with their environment. In a modality such as vision, categorization requires the generation of both selective and invariant responses of cortical neurons to complex visual stimuli. How does behavior contribute to shaping the responses of these neurons? Analysis of this question is made difficult by the complex multilevel interactions between many neural and behavioral variables. To mitigate this difficulty, we studied the development and ongoing plasticity of pattern-selective neuronal responses by means of synthetic neural modeling. For this purpose, we constructed Darwin V, which consists of a simulated neuronal model embedded in a real-world device that is capable of motion and autonomous behavior. The neuronal model consists of four major components: a visual system (containing cortical and subcortical networks); a taste system based on conductance; sets of motor neurons capable of triggering behavior; and a diffuse ascending (value) system. The modeled visual cortex consists of two areas: a topographic map responsive to elementary features connected to a higher-order map composed of initially non-selective neuronal units. During behavior over time in its environment, Darwin V encounters numerous objects consisting of black metal cubes displaying different patterns of white blobs and stripes. Initially, the lack of specific higher-order visual responses does not allow visual pattern discrimination, and appetitive and aversive behaviors are triggered by the 'taste' (surface conductivity of objects) alone. In the course of sensory experience, however, changes occur in visual and sensorimotor connection strengths, with two major consequences. First, units within the higher visual area acquire responses that are both pattern selective and translation invariant. Second, as a result of the operation of the value system, these responses become linked to appropriate behaviors. Analysis of Darwin V after such changes indicates that the continuity of self-generated movements is essential for the development of pattern-selective and translation-invariant responses. The concomitant development of a preference for foveal over parafoveal objects was found to be due to increased behavioral interactions with object cubes gripped by the centrally mounted effector (snout) of Darwin V. Finally, even after development of higher-order visual responses, visual responses to more frequently encountered objects continued to be enhanced, while other responses were diminished. Overall, the detailed study of Darwin V over multiple levels of organization provides a heuristically revealing example of the crucial role played by behavioral and environmental interactions in the development of complex responses by specialized neurons.     

On a contract model for treatment.

Finds serious problems with the suggestion by R. K. Schwitzgebel (1975) that a contract be used to define the rights and liabilities between patient and therapist in an institutional setting and notes that the courts are better at defining such ground rules. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Large-sample analysis for a stochastic epidemic model and its parameter estimators

This paper considers the simplest stochastic model for the spread of an epidemic in a closed, homogeneously mixing population. Approximate methods are presented for calculating the probability distribution of the epidemic size (i.e. number of infected individuals). In fact, a functional central limit theorem and a large deviation principle for the epidemic size when the population increases are shown. These results enable us to both obtain a global approximation for the epidemic size and study asymptotic properties of other random variables depending on the complete history of the epidemic. As an application of our results, we derive two sequences of estimators for the contact rate and analyze their asymptotic behaviour.     

大气扩散模式及其应用

在进行环境质量评价时,一般都用大气扩散模式进行预测,本文分析了影响大气扩散的气象因子,讨论了高斯模式在其基本条件发生变化时的修正方法并在实际工作中进行应用。     

A neuronal network model for the detection of single bands and cruciform figures

The model of artificial neuronal network has been proposed, which detects not only single bar orientation but also has selective sensitivity to cross-like figures. Properties of such "detector of cross" have been studied at the model constructed on the basis of convergence of excitatory connections with different weights from neurons with different orientation tuning. It has been shown that the amplification mechanism (reverberator) is necessary for the detector of cross with monomodal orientation tuning.