A biophysical observation model for field potentials of networks of leaky integrate-and-fire neurons

We present a biophysical approach for the coupling of neural network activity as resulting from proper dipole currents of cortical pyramidal neurons to the electric field in extracellular fluid. Starting from a reduced threecompartment model of a single pyramidal neuron, we derive an observation model for dendritic dipole currents in extracellular space and thereby for the dendritic field potential that contributes to the local field potential of a neural population. This work aligns and satisfies the widespread dipole assumption that is motivated by the "open-field" configuration of the dendritic field potential around cortical pyramidal cells. Our reduced three-compartment scheme allows to derive networks of leaky integrate-and-fire models, which facilitates comparison with existing neural network and observation models. In particular, by means of numerical simulations we compare our approach with an ad hoc model by Mazzoni et al. [Mazzoni, A., S. Panzeri, N. K. Logothetis, and N. Brunel (2008). Encoding of naturalistic stimuli by local field potential spectra in networks of excitatory and inhibitory neurons. PLoS Computational Biology 4 (12), e1000239], and conclude that our biophysically motivated approach yields substantial improvement.Comment: 31 pages, 4 figure

Mean field modelling of human EEG: application to epilepsy

Aggregated electrical activity from brain regions recorded via an electroencephalogram (EEG), reveal that the brain is never at rest, producing a spectrum of ongoing oscillations that change as a result of different behavioural states and neurological conditions. In particular, this thesis focusses on pathological oscillations associated with absence seizures that typically affect 2–16 year old children. Investigation of the cellular and network mechanisms for absence seizures studies have implicated an abnormality in the cortical and thalamic activity in the generation of absence seizures, which have provided much insight to the potential cause of this disease. A number of competing hypotheses have been suggested, however the precise cause has yet to be determined. This work attempts to provide an explanation of these abnormal rhythms by considering a physiologically based, macroscopic continuum mean-field model of the brain's electrical activity. The methodology taken in this thesis is to assume that many of the physiological details of the involved brain structures can be aggregated into continuum state variables and parameters. The methodology has the advantage to indirectly encapsulate into state variables and parameters, many known physiological mechanisms underlying the genesis of epilepsy, which permits a reduction of the complexity of the problem. That is, a macroscopic description of the involved brain structures involved in epilepsy is taken and then by scanning the parameters of the model, identification of state changes in the system are made possible. Thus, this work demonstrates how changes in brain state as determined in EEG can be understood via dynamical state changes in the model providing an explanation of absence seizures. Furthermore, key observations from both the model and EEG data motivates a number of model reductions. These reductions provide approximate solutions of seizure oscillations and a better understanding of periodic oscillations arising from the involved brain regions. Local analysis of oscillations are performed by employing dynamical systems theory which provide necessary and sufficient conditions for their appearance. Finally local and global stability is then proved for the reduced model, for a reduced region in the parameter space. The results obtained in this thesis can be extended and suggestions are provided for future progress in this area

Production of antibiotics and biopolymer by the bacterium Pseudomonas chlororaphis using glycerol

Members of the Pseudomonas genus are known for their ability to produce multiple secondary metabolites, including bioactive metabolites, such as antibiotics. Pseudomonas chlororaphis subsp. aurantiaca DSM 19603 is a non-pathogenic bacterium widely used as plant growth-promoting rhizobacteria that has been reported to be able to produce three products of interest, namely, antibiotics (phenazines) and two biopolymers, medium-chain-length polyhydroxyalkanoates (mcl-PHA) and exopolysaccharides (EPS). Phenazines are heterocyclic nitrogenous compounds that can act as antibiotic, antiparasitic or even anticancer agents. PHAs are a class of biobased and biodegradable polymers that depending on their composition and specific properties shows potential application on areas from thermoplastics to elastomers. EPS are a group of natural polymers mainly composed by sugars that due to their variety of physical and structural properties have many applications in industries such as food, pharmaceutical and cosmetics. This biopolymer could also be a good ally in bioremediation. The main objective of this study was to develop and optimize the bioprocess for phenazines and biopolymers (mcl-PHA and EPS) co-production by Pseudomonas chlororaphis using glycerol as carbon source. Different nutrient (nitrogen and carbon) concentrations, pH control with NH4OH and other conditions were tested in order to obtain higher productivities of all mentioned products. The study showed that the same fermentation conditions (standard nutrients concentration and pH control with NH4OH) enabled to achieve the best product concentrations, namely, a significant amount of phenazines (6.05 OD365nm), an EPS concentration of 3.8 g/L and a mcl-PHA concentration of 8.43 g/L. According to literature, this mcl-PHA concentration is the highest achieved in P. chlororaphis fermentations. Further, carbon and nitrogen concentrations in culture medium seems to impact the mcl-PHA composition, which could guarantee different properties to this polymer

Synchronization in STDP-driven memristive neural networks with time-varying topology

Synchronization is a widespread phenomenon in the brain. Despite numerous studies, the specific parameter configurations of the synaptic network structure and learning rules needed to achieve robust and enduring synchronization in neurons driven by spike-timing-dependent plasticity (STDP) and temporal networks subject to homeostatic structural plasticity (HSP) rules remain unclear. Here, we bridge this gap by determining the configurations required to achieve high and stable degrees of complete synchronization (CS) and phase synchronization (PS) in time-varying small-world and random neural networks driven by STDP and HSP. In particular, we found that decreasing $P$ (which enhances the strengthening effect of STDP on the average synaptic weight) and increasing $F$ (which speeds up the swapping rate of synapses between neurons) always lead to higher and more stable degrees of CS and PS in small-world and random networks, provided that the network parameters such as the synaptic time delay $\tau_c$, the average degree $\langle k \rangle$, and the rewiring probability $\beta$ have some appropriate values. When $\tau_c$, $\langle k \rangle$, and $\beta$ are not fixed at these appropriate values, the degree and stability of CS and PS may increase or decrease when $F$ increases, depending on the network topology. It is also found that the time delay $\tau_c$ can induce intermittent CS and PS whose occurrence is independent $F$. Our results could have applications in designing neuromorphic circuits for optimal information processing and transmission via synchronization phenomena.Comment: 28 pages, 86 references, 8 figures, 2 Table

Oralidade e letramento em uma perspectiva de inclusao social do povo Kalunga

Monografia (graduação)—Universidade de Brasília, Faculdade UnB Planaltina, Licenciatura em Educação do Campo, 2017.A Pesquisa, em foco, aborda Oralidade e Letramento em uma Perspectiva de Inclusão Social do Povo Kalunga,contextualizando a Comunidade Escolar Quilombola Tinguizal, situada no município de Monte Alegre de Goiás. A fundamentação Teórica tem como referências principais os autores: Araújo (2016); Baiocchi (2013); Bortoni-Ricardo (2009); Couto 2013; Dionísio (2007); Gil (2010); Marcuschi (2007); Rojo (2012, 2014); Salles 2014; Sousa (2006) e Triviños (1987), entre outros. O presente trabalho foi organizado conforme os procedimentos de capítulos e subtemas, entre eles: Oralidade, letramentos múltiplos, compreensão de letramento em comunidades tradicionais, contextualizando educação quilombola, análise de dados,considerações finais, entre outros aspectos comuns a um trabalho de pesquisa, de forma a entender a complexidade das problemáticas relacionadas ao tema principal. Para cada subtema é proposto referências bibliográficas de autores com afinidade e informações sistemáticas sobre os assuntos abordados, com discussão contextualizada. De modo geral, pretende-se neste trabalho dialogar o tema geral com as possibilidades de rever as práticas de ensino na comunidade quilombola, propondo aos educadores reflexão acerca do papel da escola em relação a cultural local, favorecendo assim que a oralidade e os letramentos comuns desse grupo social sejam inseridos nas práticas de ensino. O trabalho contribui para que Tinguizal e outras Comunidades Quilombolas Kalunga, tenham acesso a uma pesquisa com tema voltado a significação da aprendizagem, proporcionando a educadores, educandos e universitários, referências para possíveis estudos futuros. O trabalho contribui também para que professores e alunos possam trabalhar a temática em sala de aula com maior precisão pedagógica em comum acordo e diálogo com o currículo referência de ensino proposto para a escola nas comunidades quilombolas, em especial, Tinguizal.The research focus, covers Orality and literacy in a perspective of Social inclusion of People Kalunga, contextualizing the Quilombola Tinguizal school community, situated in the municipality of Monte Alegre de Goiás. The theoretical foundation has as main references the authors: Aguilar (2016); Baiocchi (2013); Bortoni-Ricardo (2009); Couto 2013; Dionysus (2007); Gil (2010); Depends (2007); Rojo (2012, 2014); S 2014; Sousa (2006) and Triviños (1987), among others. The present work was organized as the procedures of chapters and sub-themes, including: Orality, letramentos, literacy and comprehension letramento in traditional communities, quilombola, data analysis, final considerations, among other aspects common to a research paper, in order to understand the complexity of the problems related to the main theme. For each sub-theme proposes references to authors with affinity and systematic information on the subjects dealt with contextualized discussion. In General, this work aims to engage the general theme with the possibilities of reviewing the practices of teaching on the quilombola community, offering educators reflection about the role of the school in relation to local cultural, favoring so the orality and the common letramentos of this social group are inserted into teaching practices. The work contributes to that Tinguizal and Quilombo Kalunga communities, have access to a survey theme back the meaning of learning, providing educators, students and academics, references to possible future studies. The work also contributes to that teachers and students can work the topic into the classroom with greater precision in mutual agreement and dialogue teaching with the curriculum teaching reference proposed for the school in quilombolas communities, in particular, Tinguizal

On the genesis of spike-wave activity in a mean-field model of human brain activity

In this letter, the genesis of spike-wave activity - a hallmark of many generalized epileptic seizures - is investigated in a reduced mean-field model of human neural activity. Drawing upon brain modeling and dynamical systems theory, we demonstrate that the thalamic circuitry of the system is crucial for the generation of these abnormal rhythms, observing that the combination of inhibition from reticular nuclei and excitation from the external signal, interplay to generate the spike-wave oscillation. We demonstarte that this is a nonlinear phenomena and that linear stability analysis is not appropriate to explain such solutions