title: Dynamics and precursor signs for phase transitions in neural systems

authors: Negahbani, Ehsan

subjects: nonlinear dynamics

abstract: This thesis investigates neural state transitions associated with sleep, seizure and anaesthesia. The aim is to address the question: How does a brain traverse the critical threshold between distinct cortical states, both healthy and pathological? Specifically we are interested in sub-threshold neural behaviour immediately prior to state transition. We use theoretical neural modelling (single spiking neurons, a network of these, and a mean-field continuum limit) and in vitro experiments to address this question.
Dynamically realistic equations of motion for thalamic relay neuron, reticular nuclei, cortical pyramidal and cortical interneuron in different vigilance states are developed, based on the Izhikevich spiking neuron model. A network of cortical neurons is assembled to examine the behaviour of the gamma-producing cortical network and its transition to lower frequencies due to effect of anaesthesia. Then a three-neuron model for the thalamocortical loop for sleep spindles is presented. Numerical simulations of these networks confirms spiking consistent with reported in vivo measurement results, and provides supporting evidence for precursor indicators of imminent phase transition due to occurrence of individual spindles.
To complement the spiking neuron networks, we study the Wilson–Cowan neural mass equations describing homogeneous cortical columns and a 1D spatial cluster of such columns. The abstract representation of cortical tissue by a pair of coupled integro-differential equations permits thorough linear stability, phase plane and bifurcation analyses. This model shows a rich set of spatial and temporal bifurcations marking the boundary to state transitions: saddle-node, Hopf, Turing, and mixed Hopf–Turing. Close to state transition, white-noise-induced subthreshold fluctuations show clear signs of critical slowing down with prolongation and strengthening of autocorrelations, both in time and space, irrespective of bifurcation type.
Attempts at in vitro capture of these predicted leading indicators form the last part of the thesis. We recorded local field potentials (LFPs) from cortical and hippocampal slices of mouse brain. State transition is marked by the emergence and cessation of spontaneous seizure-like events (SLEs) induced by bathing the slices in an artificial cerebral spinal fluid containing no magnesium ions. Phase-plane analysis of the LFP time-series suggests that distinct bifurcation classes can be responsible for state change to seizure. Increased variance and growth of spectral power at low frequencies (f < 15 Hz) was observed in LFP recordings prior to initiation of some SLEs. In addition we demonstrated prolongation of electrically evoked potentials in cortical tissue, while forwarding the slice to a seizing regime. The results offer the possibility of capturing leading temporal indicators prior to seizure generation, with potential consequences for understanding epileptogenesis.
Guided by dynamical systems theory this thesis captures evidence for precursor signs of phase transitions in neural systems using mathematical and computer-based modelling as well as in vitro experiments.

text: Dynamics and precursor signs for phase transitions in neural systems This thesis investigates neural state transitions associated with sleep, seizure and anaesthesia. The aim is to address the question: How does a brain traverse the critical threshold between distinct cortical states, both healthy and pathological? Specifically we are interested in sub-threshold neural behaviour immediately prior to state transition. We use theoretical neural modelling (single spiking neurons, a network of these, and a mean-field continuum limit) and in vitro experiments to address this question.
Dynamically realistic equations of motion for thalamic relay neuron, reticular nuclei, cortical pyramidal and cortical interneuron in different vigilance states are developed, based on the Izhikevich spiking neuron model. A network of cortical neurons is assembled to examine the behaviour of the gamma-producing cortical network and its transition to lower frequencies due to effect of anaesthesia. Then a three-neuron model for the thalamocortical loop for sleep spindles is presented. Numerical simulations of these networks confirms spiking consistent with reported in vivo measurement results, and provides supporting evidence for precursor indicators of imminent phase transition due to occurrence of individual spindles.
To complement the spiking neuron networks, we study the Wilson–Cowan neural mass equations describing homogeneous cortical columns and a 1D spatial cluster of such columns. The abstract representation of cortical tissue by a pair of coupled integro-differential equations permits thorough linear stability, phase plane and bifurcation analyses. This model shows a rich set of spatial and temporal bifurcations marking the boundary to state transitions: saddle-node, Hopf, Turing, and mixed Hopf–Turing. Close to state transition, white-noise-induced subthreshold fluctuations show clear signs of critical slowing down with prolongation and strengthening of autocorrelations, both in time and space, irrespective of bifurcation type.
Attempts at in vitro capture of these predicted leading indicators form the last part of the thesis. We recorded local field potentials (LFPs) from cortical and hippocampal slices of mouse brain. State transition is marked by the emergence and cessation of spontaneous seizure-like events (SLEs) induced by bathing the slices in an artificial cerebral spinal fluid containing no magnesium ions. Phase-plane analysis of the LFP time-series suggests that distinct bifurcation classes can be responsible for state change to seizure. Increased variance and growth of spectral power at low frequencies (f < 15 Hz) was observed in LFP recordings prior to initiation of some SLEs. In addition we demonstrated prolongation of electrically evoked potentials in cortical tissue, while forwarding the slice to a seizing regime. The results offer the possibility of capturing leading temporal indicators prior to seizure generation, with potential consequences for understanding epileptogenesis.
Guided by dynamical systems theory this thesis captures evidence for precursor signs of phase transitions in neural systems using mathematical and computer-based modelling as well as in vitro experiments.

year: 2014

title: The social benefits of informal and lifestyle sports: a research agenda [Editorial]

authors: Gilchrist, Paul

abstract: Understanding sport through the lens of social benefit has become a mainstay of sport policy analysis. A wealth of research has considered how sport contributes to achieving wider social benefits, including improvements to health and well-being, life satisfaction, crime reduction, community cohesion and activism, environmental stewardship, educational attainment, labour market participation, civic renewal, urban regeneration and developing youth (Coalter 2007, Oughton and Tacon 2007 Oughton, Brookes and Wiggan ). Over the decades governments and policymakers have advocated the use of traditional or mainstream sports for combating a range of social ‘problems’, from youth disengagement to poor health. Most recently, fears about rising levels of inactivity and obesity, particularly amongst children, are increasingly driving sports-based interventions and the question of sport’s capacity to deliver public policy outcomes

text: The social benefits of informal and lifestyle sports: a research agenda [Editorial] Understanding sport through the lens of social benefit has become a mainstay of sport policy analysis. A wealth of research has considered how sport contributes to achieving wider social benefits, including improvements to health and well-being, life satisfaction, crime reduction, community cohesion and activism, environmental stewardship, educational attainment, labour market participation, civic renewal, urban regeneration and developing youth (Coalter 2007, Oughton and Tacon 2007 Oughton, Brookes and Wiggan ). Over the decades governments and policymakers have advocated the use of traditional or mainstream sports for combating a range of social ‘problems’, from youth disengagement to poor health. Most recently, fears about rising levels of inactivity and obesity, particularly amongst children, are increasingly driving sports-based interventions and the question of sport’s capacity to deliver public policy outcomes

year: 2017

title: The sociocultural impact of tourism on the Te Arawa people of Rotorua, New Zealand

authors: Te Awekotuku, Ngahuia

subjects: Te Arawa

abstract: This is a study of how tourism in New Zealand has affected a major tribal community; their insights, reactions, and experiences. Covering five generations, it presents an oral account of the actively concerned social groups. Wherever possible, or necessary, this is reiterated and reinforced by the written record.

The work comprises two parts, the first which outlines the historic background according to available documentation, and the second which focusses on particular aspects of tribal culture and experience. Material for this section, otherwise unrecorded, came from the narrated stories, reminiscences, and often shrewd observations of the people themselves. It deals with residential community, song and dance, arts and crafts, and the role of women.

As an essentially ethnographic commentary, the study does not examine the economic features or effects of tourism, except where fiscal factors are pertinent to the understanding or continuity of the Te Arawa experience of the tourist world.

text: The sociocultural impact of tourism on the Te Arawa people of Rotorua, New Zealand This is a study of how tourism in New Zealand has affected a major tribal community; their insights, reactions, and experiences. Covering five generations, it presents an oral account of the actively concerned social groups. Wherever possible, or necessary, this is reiterated and reinforced by the written record.

The work comprises two parts, the first which outlines the historic background according to available documentation, and the second which focusses on particular aspects of tribal culture and experience. Material for this section, otherwise unrecorded, came from the narrated stories, reminiscences, and often shrewd observations of the people themselves. It deals with residential community, song and dance, arts and crafts, and the role of women.

As an essentially ethnographic commentary, the study does not examine the economic features or effects of tourism, except where fiscal factors are pertinent to the understanding or continuity of the Te Arawa experience of the tourist world.

year: 1981