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: Searching for patterns in political event sequences: Experiments with the KEDs database

authors: Kovar, Klaus

subjects: computer science

abstract: This paper presents an empirical study on the possibility of discovering interesting event sequences and sequential rules in a large database of international political events. A data mining algorithm first presented by Mannila and Toivonen (1996), has been implemented and extended, which is able to search for generalized episodes in such event databases. Experiments conducted with this algorithm on the Kansas Event Data System (KEDS) database, an event data set covering interactions between countries in the Persian Gulf region, are described. Some qualitative and quantitative results are reported, and experiences with strategies for reducing the problem complexity and focusing on the search on interesting subsets of events are described.

text: Searching for patterns in political event sequences: Experiments with the KEDs database This paper presents an empirical study on the possibility of discovering interesting event sequences and sequential rules in a large database of international political events. A data mining algorithm first presented by Mannila and Toivonen (1996), has been implemented and extended, which is able to search for generalized episodes in such event databases. Experiments conducted with this algorithm on the Kansas Event Data System (KEDS) database, an event data set covering interactions between countries in the Persian Gulf region, are described. Some qualitative and quantitative results are reported, and experiences with strategies for reducing the problem complexity and focusing on the search on interesting subsets of events are described.

year: 2000

title: The thing’s revelation: Some thoughts on Māori philosophical research

authors: Mika, Carl Te Hira

abstract: In indigenous research projects, there is a strong emphasis on interviews and the analysis of the data that results. There is, however, another form of research that still calls to be fully acknowledged. Philosophical research shares some ground with empirical because it responds to a Maori history and experience of oppression. One clear area in which it may differ, though, is in how it attempts to acknowledge the presence of ‘things’, which we might call our ‘whanaunga’ (relations), even where these have been deemed by Western science to be inanimate. More importantly, philosophical research is risky because the thing continues to influence the researching self, despite the self’s eventual disengagement from the research. Philosophical research – the kind that seeks an unobtainable ground of thought – is at once aware of and tentative towards the thing. It also acts within the influence of the thing: this phenomenon for the author can be best felt when the bizarre is encountered in everyday observations.

text: The thing’s revelation: Some thoughts on Māori philosophical research In indigenous research projects, there is a strong emphasis on interviews and the analysis of the data that results. There is, however, another form of research that still calls to be fully acknowledged. Philosophical research shares some ground with empirical because it responds to a Maori history and experience of oppression. One clear area in which it may differ, though, is in how it attempts to acknowledge the presence of ‘things’, which we might call our ‘whanaunga’ (relations), even where these have been deemed by Western science to be inanimate. More importantly, philosophical research is risky because the thing continues to influence the researching self, despite the self’s eventual disengagement from the research. Philosophical research – the kind that seeks an unobtainable ground of thought – is at once aware of and tentative towards the thing. It also acts within the influence of the thing: this phenomenon for the author can be best felt when the bizarre is encountered in everyday observations.

year: 2015