title: Gap junctions mediate large-scale Turing structures in a mean-field cortex driven by subcortical noise

authors: Steyn-Ross, Moira L.

subjects: electroencephalogram

abstract: One of the grand puzzles in neuroscience is establishing the link between cognition and the disparate patterns of spontaneous and task-induced brain activity that can be measured clinically using a wide range of detection modalities such as scalp electrodes and imaging tomography. High-level brain function is not a single-neuron property, yet emerges as a cooperative phenomenon of multiply-interacting populations of neurons. Therefore a fruitful modeling approach is to picture the cerebral cortex as a continuum characterized by parameters that have been averaged over a small volume of cortical tissue. Such mean-field cortical models have been used to investigate gross patterns of brain behavior such as anesthesia, the cycles of natural sleep, memory and erasure in slow-wave sleep, and epilepsy. There is persuasive and accumulating evidence that direct gap-junction connections between inhibitory neurons promote synchronous oscillatory behavior both locally and across distances of some centimeters, but, to date, continuum models have ignored gap-junction connectivity. In this paper we employ simple mean-field arguments to derive an expression for D2, the diffusive coupling strength arising from gap-junction connections between inhibitory neurons. Using recent neurophysiological measurements reported by Fukuda et al. [J. Neurosci. 26, 3434 (2006)], we estimate an upper limit of D2 0.6  cm2. We apply a linear stability analysis to a standard mean-field cortical model, augmented with gap-junction diffusion, and find this value for the diffusive coupling strength to be close to the critical value required to destabilize the homogeneous steady state. Computer simulations demonstrate that larger values of D2 cause the noise-driven model cortex to spontaneously crystalize into random mazelike Turing structures: centimeter-scale spatial patterns in which regions of high-firing activity are intermixed with regions of low-firing activity. These structures are consistent with the spatial variations in brain activity patterns detected with the BOLD (blood oxygen–level–dependent) signal detected with magnetic resonance imaging, and may provide a natural substrate for synchronous gamma-band rhythms observed across separated EEG (electroencephalogram) electrodes.

text: Gap junctions mediate large-scale Turing structures in a mean-field cortex driven by subcortical noise One of the grand puzzles in neuroscience is establishing the link between cognition and the disparate patterns of spontaneous and task-induced brain activity that can be measured clinically using a wide range of detection modalities such as scalp electrodes and imaging tomography. High-level brain function is not a single-neuron property, yet emerges as a cooperative phenomenon of multiply-interacting populations of neurons. Therefore a fruitful modeling approach is to picture the cerebral cortex as a continuum characterized by parameters that have been averaged over a small volume of cortical tissue. Such mean-field cortical models have been used to investigate gross patterns of brain behavior such as anesthesia, the cycles of natural sleep, memory and erasure in slow-wave sleep, and epilepsy. There is persuasive and accumulating evidence that direct gap-junction connections between inhibitory neurons promote synchronous oscillatory behavior both locally and across distances of some centimeters, but, to date, continuum models have ignored gap-junction connectivity. In this paper we employ simple mean-field arguments to derive an expression for D2, the diffusive coupling strength arising from gap-junction connections between inhibitory neurons. Using recent neurophysiological measurements reported by Fukuda et al. [J. Neurosci. 26, 3434 (2006)], we estimate an upper limit of D2 0.6  cm2. We apply a linear stability analysis to a standard mean-field cortical model, augmented with gap-junction diffusion, and find this value for the diffusive coupling strength to be close to the critical value required to destabilize the homogeneous steady state. Computer simulations demonstrate that larger values of D2 cause the noise-driven model cortex to spontaneously crystalize into random mazelike Turing structures: centimeter-scale spatial patterns in which regions of high-firing activity are intermixed with regions of low-firing activity. These structures are consistent with the spatial variations in brain activity patterns detected with the BOLD (blood oxygen–level–dependent) signal detected with magnetic resonance imaging, and may provide a natural substrate for synchronous gamma-band rhythms observed across separated EEG (electroencephalogram) electrodes.

year: 2007

title: Using formal models to design user interfaces a case study

authors: Bowen, Judy

subjects: computer science

abstract: The use of formal models for user interface design can provide a number of benefits. It can help to ensure consistency across designs for multiple platforms, prove properties such as reachability and completeness and, perhaps most importantly, can help incorporate the user interface design process into a larger, formally-based, software development process. Often, descriptions of such models and examples are presented in isolation from real-world practice in order to focus on particular benefits, small focused examples or the general methodology. This paper presents a case study of developing the user interface to a new software application using a particular pair of formal models, presentation models and presentation interaction models. The aim of this study was to practically apply the use of formal models to the design process of a UI for a new software application. We wanted to determine how easy it would be to integrate such models into our usual development process and to find out what the benefits, and difficulties, of using such models were. We will show how we used the formal models within a user-centred design process, discuss what effect they had on this process and explain what benefits we perceived from their use.

text: Using formal models to design user interfaces a case study The use of formal models for user interface design can provide a number of benefits. It can help to ensure consistency across designs for multiple platforms, prove properties such as reachability and completeness and, perhaps most importantly, can help incorporate the user interface design process into a larger, formally-based, software development process. Often, descriptions of such models and examples are presented in isolation from real-world practice in order to focus on particular benefits, small focused examples or the general methodology. This paper presents a case study of developing the user interface to a new software application using a particular pair of formal models, presentation models and presentation interaction models. The aim of this study was to practically apply the use of formal models to the design process of a UI for a new software application. We wanted to determine how easy it would be to integrate such models into our usual development process and to find out what the benefits, and difficulties, of using such models were. We will show how we used the formal models within a user-centred design process, discuss what effect they had on this process and explain what benefits we perceived from their use.

year: 2007

title: A report to iwi on the kaupapa Māori environmental outcomes and indicators kete

authors: Jefferies, Richard

subjects: New Zealand

abstract: Tangata whenua in Aotearoa have been largely excluded from participation in local government  planning since colonisation, but tikanga and Māori values have for the past two decades been acknowledged in resource management and local government legislation, especially the Resource Management Act, 1991 (RMA) and Local Government Act, 2002 (LGA). For example, the RMA has provisions in over 30 sections for councils to give effect to Māori interests.

In practice, however, there is widespread concern that despite these provisions, Māori are largely excluded from local government resource management processes and their values subordinated to those of the wider community, particularly western scientific values.

This report describes research that resulted in a kaupapa Māori outcomes and indicators framework, and associated methods, that can be used by iwi to assess the quality of statutory plans and the environmental performance of councils in their rohe.

text: A report to iwi on the kaupapa Māori environmental outcomes and indicators kete Tangata whenua in Aotearoa have been largely excluded from participation in local government  planning since colonisation, but tikanga and Māori values have for the past two decades been acknowledged in resource management and local government legislation, especially the Resource Management Act, 1991 (RMA) and Local Government Act, 2002 (LGA). For example, the RMA has provisions in over 30 sections for councils to give effect to Māori interests.

In practice, however, there is widespread concern that despite these provisions, Māori are largely excluded from local government resource management processes and their values subordinated to those of the wider community, particularly western scientific values.

This report describes research that resulted in a kaupapa Māori outcomes and indicators framework, and associated methods, that can be used by iwi to assess the quality of statutory plans and the environmental performance of councils in their rohe.

year: 2009-06-30