Addolorata Marasco

On the mechanisms underlying the depolarization block in the spiking dynamics of CA1 pyramidal neurons

Under sustained input current of increasing strength neurons eventually stop firing, entering a depolarization block. This is a robust effect that is not usually explored in experiments or explicitly implemented or tested in models. However, the range of current strength needed for a depolarization block could be easily reached with a random background activity of only a few hundred excitatory synapses. Depolarization block may thus be an important property of neurons that should be better characterized in experiments and explicitly taken into account in models at all implementation scales. Here we analyze the spiking dynamics of CA1 pyramidal neuron models using the same set of ionic currents on both an accurate morphological reconstruction and on its reduction to a single-compartment. The results show the specific ion channel properties and kinetics that are needed to reproduce the experimental findings, and how their interplay can drastically modulate the neuronal dynamics and the input current range leading to a depolarization block. We suggest that this can be one of the rate-limiting mechanisms protecting a CA1 neuron from excessive spiking activity.

Negative plant soil feedback explaining ring formation in clonal plants

Ring shaped patches of clonal plants have been reported in different environments, but the mechanisms underlying such pattern formation are still poorly explained. Water depletion in the inner tussocks zone has been proposed as a possible cause, although ring patterns have been also observed in ecosystems without limiting water conditions. In this work, a spatially explicit model is presented in order to investigate the role of negative plant-soil feedback as an additional explanation for ring formation. The model describes the dynamics of the plant biomass in the presence of toxicity produced by the decomposition of accumulated litter in the soil. Our model qualitatively reproduces the emergence of ring patterns of a single clonal plant species during colonisation of a bare substrate. The model admits two homogeneous stationary solutions representing bare soil and uniform vegetation cover which depend only on the ratio between the biomass death and growth rates. Moreover, differently from other plant spatial patterns models, but in agreement with real field observations of vegetation dynamics, we demonstrated that the pattern dynamics always lead to spatially homogeneous vegetation covers without creation of stable Turing patterns. Analytical results show that ring formation is a function of two main components, the plant specific susceptibility to toxic compounds released in the soil by the accumulated litter and the decay rate of these same compounds, depending on environmental conditions. These components act at the same time and their respective intensities can give rise to the different ring structures observed in nature, ranging from slight reductions of biomass in patch centres, to the appearance of marked rings with bare inner zones, as well as the occurrence of ephemeral waves of plant cover. Our results highlight the potential role of plant-soil negative feedback depending on decomposition processes for the development of transient vegetation patterns.

A numerical approach to nonlinear two-point boundary value problems for ODEs

In this paper we propose a numerical approach to solve some problems connected with the implementation of the Newton type methods for the resolution of the nonlinear system of equations related to the discretization of a nonlinear two-point BVPs for ODEs with mixed linear boundary conditions by using the finite difference method.

Vegetation Pattern Formation Due to Interactions Between Water Availability and Toxicity in Plant–Soil Feedback

Development of a comprehensive theory of the formation of vegetation patterns is still in progress. A prevailing view is to treat water availability as the main causal factor for the emergence of vegetation patterns. While successful in capturing the occurrence of multiple vegetation patterns in arid and semiarid regions, this hypothesis fails to explain the presence of vegetation patterns in humid environments. We explore the rich structure of a toxicity-mediated model of the vegetation pattern formation. This model consists of three PDEs accounting for a dynamic balance between biomass, water, and toxic compounds. Different (ecologically feasible) regions of the model’s parameter space give rise to stable spatial vegetation patterns in Turing and non-Turing regimes. Strong negative feedback gives rise to dynamic spatial patterns that continuously move in space while retaining their stable topology.

On the acceleration waves in second-order elastic, isotropic, compressible, and homogeneous materials

In this paper we propose a Signorinis perturbation method to investigate the propagation of acceleration waves in second-order elastic, isotropic, compressible, and homogeneous materials. The method is applied when the undisturbed region is subjected to a simple extension or to a simple shear. In these cases, we evaluate the first-order terms of the speeds and the amplitudes of the acceleration waves in any arbitrary direction of propagation.

Synaptic clusters function as odor operators in the olfactory bulb

Significance How the olfactory bulb organizes and processes odor inputs through fundamental operations of its microcircuits is still controversial. To reveal these operations we hypothesize that one of the key mechanisms underlying odor coding is the interaction among spatially restricted and well-defined clusters of potentiated mitral–granule cell synapses. These experimentally observed clusters selectively gate the propagation of neuronal activity within the olfactory bulb and extensively contribute to sculpting the mitral cell output to the cortex. We show and discuss how their interaction and computational roles can be described by a theoretical framework that can be used to derive, analyze, and predict the olfactory bulb network operations on an odor input. How the olfactory bulb organizes and processes odor inputs through fundamental operations of its microcircuits is largely unknown. To gain new insight we focus on odor-activated synaptic clusters related to individual glomeruli, which we call glomerular units. Using a 3D model of mitral and granule cell interactions supported by experimental findings, combined with a matrix-based representation of glomerular operations, we identify the mechanisms for forming one or more glomerular units in response to a given odor, how and to what extent the glomerular units interfere or interact with each other during learning, their computational role within the olfactory bulb microcircuit, and how their actions can be formalized into a theoretical framework in which the olfactory bulb can be considered to contain “odor operators” unique to each individual. The results provide new and specific theoretical and experimentally testable predictions.

Using Strahler's analysis to reduce up to 200-fold the run time of realistic neuron models

The cellular mechanisms underlying higher brain functions/dysfunctions are extremely difficult to investigate experimentally, and detailed neuron models have proven to be a very useful tool to help these kind of investigations. However, realistic neuronal networks of sizes appropriate to study brain functions present the major problem of requiring a prohibitively high computational resources. Here, building on our previous work, we present a general reduction method based on Strahlers analysis of neuron morphologies. We show that, without any fitting or tuning procedures, it is possible to map any morphologically and biophysically accurate neuron model into an equivalent reduced version. Using this method for Purkinje cells, we demonstrate how run times can be reduced up to 200–fold, while accurately taking into account the effects of arbitrarily located and activated synaptic inputs.

On the first-order speeds in any directions of acceleration waves in prestressed second-order isotropic, compressible, and homogeneous materials

In this paper, using the perturbation method we proposed in [A. Marasco, A. Romano, On the ordinary waves in second-order elastic, isotropic, compressible, and homogeneous materials, Math. Comput. Modelling 49 (7-8) (2009) 1504-1518], the first-order terms of the speeds and the amplitude of the principal waves and of the waves in any propagation direction are determined in second-order elastic, isotropic, compressible, and homogeneous materials. Moreover, for the general waves we determine the relations among the second-order constitutive constants which ensure that the waves are longitudinal or transverse.

Balance laws for continua with an interface deduced from multiphase continuous models with a transition layer

Abstract A moving transition layer (i.e., a thin three-dimensional interphase region) is investigated in order to replace it by a moving singular non-material surface endowed with thermomechanical properties. By such an analysis, we are able to attain both a general balance law, which holds in the theory of continuous systems with an interface, and a new time differentiation formula for surface integrals evaluated over evolving non-material two-dimensional continua.

Nonlinear hydrodynamic models of traffic flow in the presence of tollgates

A nonlinear hydrodynamic model of traffic flow is here proposed in order to refine the modeling of drivers behaviour. This model is able to describe the car density and flow evolution in the presence of tollgates too. In any case, the associate evolution problem is a classical Dirichlet problem related to the flow measurement. Numerical simulations related to the solution of initial-boundary value problems are obtained by employing a scientific program written by the software Mathematica.