329 research outputs found
Exploring the effect of ionic diffusion on extracellular potentials in the brain
No full textIonic concentration gradients can exist in the extracellular space (ECS) due to neuronal activity that can change the local ionic composition. Diffusion and electrical drift are two processes that move ions around in the extracellular space. These processes can be described by the Nernst-Planck equation. Ions diffuse along concentration gradients. Since ions carry charge, this process can give rise to electric currents, which, in turn, can result in a diffusion potential.
The question under investigation is if diffusion potentials in ECS are large enough to affect the measurements of local field potentials (LFPs) in the brain? Diffusion potentials are slow-changing potentials, so its possible contributions to the LFPs would be for low frequencies [1]. To explore the effect of diffusion potentials, I compared power spectrum densities (PSDs) of diffusion potentials to PSDs of LFPs recordings.
I estimated the diffusion potentials from extracellular concentration data collected from various articles. The concentration data were obtained from different experiments. Instead of numerically simulating how the diffusion potential changed, I approximated the diffusion potential by an exponentially decaying function. For more realistic estimates, I used time constants from temporal concentration data. Then, I estimated the PSDs of the diffusion potentials from each data set.
For LFP data, I found and used data files with LFP recordings. For these data files, I calculated average PSDs. In addition, I collected LFP data represented as PSDs from figures in articles,
At low frequencies (< 1 Hz), I found that PSD of the highest diffusion potentials had similar powers as the lowest PSDs of LFP measurements. Therefore, there may be a slight possibility that diffusion potentials can contribute to the LFP at the lowest frequencies.
I also estimated diffusion potentials at pathological conditions, such as spreading depression (SD), where concentration gradients are extremely large. I used the same approach and found that the diffusion potentials in these cases could be up to 10 times larger. The PSDs of the pathological diffusion potentials had similar powers as the LFP recordings.M-M
Exploring the electric diffusion potential in the extracellular space of the brain
No full textIntense neuronal signalling may locally change the ionic composition of the extracellular space, and produce ionic concentration gradients. The ionic concentration gradients causes an electric diffusion potential, described by the Nernst--Planck equation. I have modelled this diffusion potential, by combining the Nernst--Planck equation with Kirchoff's law of current conservation, this is what is called the Kirchoff--Nernst--Planck-formalism \cite{Halnes2013}\cite{Halnes2016}. By assuming a laminar structure of the cortex, I made a one-dimensional model of the diffusion potential. The potential was simulated by implementing a numerical scheme in Python. I have found recorded concentration profiles from previously published experiments, where the extracellular concentration gradients were high, but not pathologically high. I used these concentration profiles as initial conditions. The aim of this project has been to investigate whether the diffusion potential makes up a measurable part of the extracellular potential. From previous studies \cite{Halnes2016}\cite{Gratiy2017}, I know that the diffusion potential has low frequencies, and its effect would be in the low-frequency part of the extracellular potential -- the local field potential. The the frequencies of the local field potential were analyzed by computing the power spectrum density. I found that for recordable frequencies (from 0.3 Hz and above) and non-pathological ion concentration gradients, the diffusion potential was much smaller than measured local field potential.
The concentration gradients are transient, and the baseline concentrations are re-established approximately hundred times faster than what diffusion accounts for \cite{CordingleySomjen}. I simulated a diffusion potential caused by exponentially decaying concentration gradients, with typical half-lives from previous experiments. This produced a diffusion potential with higher powers in the range of the recordable frequencies, but still not at the level of the recorded local field potential.
Some pathological conditions are associated with extreme concentration gradients. I have used a recorded concentration profile where the deviations from baseline concentrations were approximately ten times higher than the non-pathological concentration deviations. I saw that in this case, the diffusion potential was of the same magnitude as the local field potential, and even larger, for frequencies lower than approximately 2 Hz. I also tried this extreme scenario with exponentially decaying concentration gradients. This resulted in a diffusion potential which was larger than the local field potential for almost all frequencies in the range of the simulation.M-LU
Comparing different techniques for stimulating neurons - a computational study
No full textA comparison of different techniques for stimulating neurons using a computational model. The computational model is an expanded version of the electrodiffusive Pinsky-Rinzel model from Sætra et al. (2020) referenced in the thesis. The explicit modeling of ion concentrations allows for comparison of which ions are used for stimulation. The expansion of the model allows for comparison of stimulation currents coming from inside and outside the system. In conclusion, both the ion mix in the stimulation current and the stimulation technique can have an effect on the response of the model. In particular, there is an effect of potassium ions in the stimulation current
Biological network modelling
No full textThis study takes a network approach to understanding complex biological systems. The overall objective is to explore how the stability and flexibility of biological networks emerge from underlying structural and dynamical characteristics. The thesis is arranged as a journey into the complexity of biological network models. The starting point is qualitative structural network descriptions. The level of detail in the dynamical description of node properties is then gradually increased. Along this journey, new features, both structural and dynamical, are revealed as crucial for the function of biological networks. A set of constructional properties are defined: structural principles, structural complexity, interaction diversity, node diversity and network density. These constructional properties capture important aspects of the structural organization and dynamic mechanisms in biological networks. A set of functional properties are defined: structural robustness, structural cyclicity, dynamic stability and dynamic flexibility. These functional properties are systemic properties that are all related to the stability of biological networks. These two sets of properties are used to demonstrate how the construction of biological networks is crucial for their function. The general theory is applied to food web and neural network models, where the general network properties are given specific biological meanings. The studies within both fields have their system specific objectives. A simple food web model is developed for explicitly including a compartment for dead organic material (detritus). Several constructional properties are revealed as crucial for the structural robustness, the structural cyclicity and the dynamic stability of food webs. The pathways due to decomposing and recycling of detritus alter the constructional properties, and are crucial for food web function. Computational neural network models are developed for clinical applications. Possible mechanisms behind electroconvulsive treatment (ECT) and anaesthetics are modelled. Clinical observations are qualitatively reproduced. Several aspects of the constructional properties of neural networks are revealed as crucial for optimal stability and flexibility of neurodynamics
Strong anonymity and infinite streams.
No full textThe extended rank-discounted utilitarian social welfare order introduced and axiomatized by Stéphane Zuber and Geir B. Asheim satisfies strong anonymity (J. Econ. Theory (2011), doi:10.1016/j.jet.2011.08.001). We question the appropriateness of strong anonymity in the context of a countably infinite sequence of subsequent generations. A modified criterion that is incomplete and satisfies finite anonymity is presented.
Nynorsk samtidslitteratur og skriftkultur. Festskrift til Geir Hjorthol
No full textThis issue of Skriftkultur stems from our desire to honor our good colleague Geir Hjorthol with a festschrift on the occasion of his 70th birthday. As the recipient is a professor of literature and also interested in literary culture studies more generally, we have titled the issue Norwegian Nynorsk contemporary literature and written culture.
Geir Hjorthol is himself responsible for the first article, in which he focuses on the role of music within Jon Fosses' novel, Septologien (2019–2022). This article became no less relevant when, a few weeks prior to completion of the issue, Fosse received the Nobel Prize in Literature 2023, the first Norwegian Nynorsk author in the prize’s history.
In the second article, Jan Inge Sørbø questions whether reading literature may be stuck in a critical rut, where one is constantly occupied with revealing something hidden in the text.
The four subsequent articles explore various recent Norwegian Nynorsk novels or authorships. In the first of these, Elin Stengrundet reflects on how Erlend Skjetne's young adult novel Eit anna blikk (2021) connects to modern migration literature and the Norwegian Nynorsk literary tradition, while Nora Simonhjell's article sheds new light on the inner coherence in the authorship of Olaug Nilssen. Marit Brekke and Wenke Mork Rogne present a post-humanistic reading of the Is-slottet (1963) by Tarjei Vesaas, while Beatrice G. Reed examines the precence of nature in Norwegian Nynorsk picture books for children in our time by taking a closer look at 13 prize-winning Norwegian Nynorsk picture books published up until the year 2000.
Non-fiction and the topic of translation are covered by the next two articles. Brage Egil Herlofsen discusses the relationship between Norwegian Nynorsk literary culture and the essay genre, based on two books from the Norsk røyndom-series published by Samlaget (2018), while Marie Nedregotten Sørbø analyzes translations of Jane Austen from English to Norwegian nynorsk in light of literary cultural and hermeneutical perspectives.
In the last article, Stian Hårstad shows how the language culture of our time places emphasis on increased pluralization, not least through the rise of digital technology, which facilitates new forms of interaction via writing, before discussing possible consequences this may have for written culture in general, and for studies of written cultures
Sustainability : ethical foundations and economic properties
No full textThe author interprets development to be sustainable if it involves a nondecreasing quality of life. He introduces a concept of justice, and shows that a development path must be sustainable to prevent injustice. He argues, and illustrates through growth models, that altruism alone does not - even in the context of an economically efficient market economy - ensure sustainability. In particular, technologies with complementarity between manmade and natural capital represent cases where sustainability need not result. Thus, policies aimed at economic efficiency, such as internalizing external effects, need not generate sustainable development. The author argues that a positive interest rate is not inconsistent with sustainable development. He also maintains that, even in a perfect market economy, prices may not convey whether investments in manmade capital are sufficient to compensate for the depletion of natural capital. In particular, a non-negative market value of net investment is not sufficient for the present quality of life to be sustainable. Finally, he emphasizes that public policy aimed at sustainable development should strengthen the mechanisms for redistribution from the present to the future.Economic Theory&Research,Environmental Economics&Policies,Banks&Banking Reform,International Terrorism&Counterterrorism,Development Economics&Aid Effectiveness
Competing conventions: The Big Branders’ struggle to incorporate new quality conceptions in the Norwegian food market
No full textThe paper addresses recent changes in the Norwegian agrifood industry from the analytical perspective of quality conventions. Storper and Salais’ “worlds of production” plus Boltanski and Thévenots’ “orders of worth” are used as a basis for the empirical study. First, the paper discusses how the largest Norwegian branders try to strategically adapt to “novel” quality attributes like health-enhancing food, origin/terroir, environmental sustainability and ethics. Second, the paper investigates the companies’ quality signalling strategy: How are these “novel” qualities communicated to consumers? Multiple options are available: Do they attempt to systematically incorporate “novel qualities” into their private brand equity (“conventionalizing qualities”)? Do they prefer a co-labelling scheme with a third party control, or do they use any other measures for quality signalling? The paper thereby discusses how the largest Norwegian branders in the food sector cope with conflicting and competing quality conventions.Food quality, economics of convention., Food Consumption/Nutrition/Food Safety,
Geir Sigurđsson: Confucian Propriety and Ritual Learning: A Philosophical Interpretation
No full textEven though the book was published more than three years ago, it is still quite topical and unsurpassed. The Outstanding Book Award, which was presented to it last year by the Society of Professors of Education, was therefore well deserved and not surprising. In this work, Geir Sigurđsson reconstructs the meaning, the role and the manifold significance of the Confucian rituality by considering the spatial and temporal context of the present situation. This does not only mean that he wants to elaborate upon the question of what can Confucian rituality “still” offer to the present humankind, and to select those elements of this rich classical tradition that could prove themselves to be most “useful” and “worthwhile” for such endeavors. It rather means that the author aims to offer the readers his own, often quite topical philosophical insights created upon the inspirational foundations of classical Confucian texts. In this context, he proposes a reconsideration of the notion Li, which belongs to the most controversial concepts in the Confucian thought
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