title: Theoretical electroencephalogram stationary spectrum for a white-noise-driven cortex: Evidence for a general anesthetic-induced phase transition

authors: Steyn-Ross, Moira L.

subjects: electroencephalogram

abstract: We present a model for the dynamics of a cerebral cortex in which inputs to neuronal assemblies are treated as random Gaussian fluctuations about a mean value. We incorporate the effect of general anesthetic agents on the cortex as a modulation of the inhibitory neurotransmitter rate constant. Stochastic differential equations are derived for the state variable he, the average excitatory soma potential, coherent fluctuations of which are believed to be the source of scalp-measured electroencephalogram (EEG) signals. Using this stochastic approach we derive a stationary (long-time limit) fluctuation spectrum for he. The model predicts that there will be three distinct stationary (equilibrium) regimes for cortical activity. In region I (“coma”), corresponding to a strong inhibitory anesthetic effect, he is single valued, large, and negative, so that neuronal firing rates are suppressed. In region II for a zero or small anesthetic effect, he can take on three values, two of which are stable; we label the stable solutions as “active” (enhanced firing) and “quiescent” (suppressed firing). For region III, corresponding to negative anesthetic (i.e., analeptic) effect, he again becomes single valued, but is now small and negative, resulting in strongly elevated firing rates (“seizure”). If we identify region II as associated with the conscious state of the cortex, then the model predicts that there will be a rapid transit between the active-conscious and comatose unconscious states at a critical value of anesthetic concentration, suggesting the existence of phase transitions in the cortex. The low-frequency spectral power in the he signal should increase strongly during the initial stage of anesthesia induction, before collapsing to much lower values after the transition into comatose-unconsciousness. These qualitative predictions are consistent with clinical measurements by Bührer et al. [Anaesthesiology 77, 226 (1992)], MacIver et al. [ibid. 84, 1411 (1996)], and Kuizenga et al. [Br. J. Anaesthesia 80, 725 (1998)]. This strong increase in EEG spectral power in the vicinity of the critical point is similar to the divergences observed during thermodynamic phase transitions. We show that the divergence in low-frequency power in our model is a natural consequence of the existence of turning points in the trajectory of stationary states for the cortex.

text: Theoretical electroencephalogram stationary spectrum for a white-noise-driven cortex: Evidence for a general anesthetic-induced phase transition We present a model for the dynamics of a cerebral cortex in which inputs to neuronal assemblies are treated as random Gaussian fluctuations about a mean value. We incorporate the effect of general anesthetic agents on the cortex as a modulation of the inhibitory neurotransmitter rate constant. Stochastic differential equations are derived for the state variable he, the average excitatory soma potential, coherent fluctuations of which are believed to be the source of scalp-measured electroencephalogram (EEG) signals. Using this stochastic approach we derive a stationary (long-time limit) fluctuation spectrum for he. The model predicts that there will be three distinct stationary (equilibrium) regimes for cortical activity. In region I (“coma”), corresponding to a strong inhibitory anesthetic effect, he is single valued, large, and negative, so that neuronal firing rates are suppressed. In region II for a zero or small anesthetic effect, he can take on three values, two of which are stable; we label the stable solutions as “active” (enhanced firing) and “quiescent” (suppressed firing). For region III, corresponding to negative anesthetic (i.e., analeptic) effect, he again becomes single valued, but is now small and negative, resulting in strongly elevated firing rates (“seizure”). If we identify region II as associated with the conscious state of the cortex, then the model predicts that there will be a rapid transit between the active-conscious and comatose unconscious states at a critical value of anesthetic concentration, suggesting the existence of phase transitions in the cortex. The low-frequency spectral power in the he signal should increase strongly during the initial stage of anesthesia induction, before collapsing to much lower values after the transition into comatose-unconsciousness. These qualitative predictions are consistent with clinical measurements by Bührer et al. [Anaesthesiology 77, 226 (1992)], MacIver et al. [ibid. 84, 1411 (1996)], and Kuizenga et al. [Br. J. Anaesthesia 80, 725 (1998)]. This strong increase in EEG spectral power in the vicinity of the critical point is similar to the divergences observed during thermodynamic phase transitions. We show that the divergence in low-frequency power in our model is a natural consequence of the existence of turning points in the trajectory of stationary states for the cortex.

year: 1999

title: When salient science is not enough to advance climate change adaptation: Lessons from Brazil and Australia

authors: Serrao-Neumann, Silvia

subjects: Boundary organisation

abstract: Increased social and environmental vulnerability to extreme climatic events and inherent aggravation of environmental and social problems has placed climate change adaptation as an urgent challenge for decision-makers. Understanding and using climate change information to advance the implementation of climate-friendly policies further compounds this challenge. A rich scholarly literature focusing on climate change adaptation endorses that investing in mechanisms that narrow the gap between climate change information production and its use is crucial to increase adaptive capacity. Based on this assumption, this paper investigates the extent to which two collaborative projects that functioned as boundary organisations in Brazil (CiAdapta project) and Australia (Climate Change Adaptation for Natural Resource Management in East Coast Australia) increased access to information, and enabled the continual and continuous usefulness of produced knowledge for climate change adaptation. Considering the distinction between usable and useful information, we applied six criteria to guide the data analysis and extract key lessons from each project. Our findings confirm that face-to-face interactions are more likely to result in research having the societal impact that is being increasingly required by research and funding bodies. Our findings also indicate that two key systemic changes are critical for the long-term influence of boundary organisations for advancing climate change adaptation. These include changes to the science, knowledge production process; and shift in the political culture.

text: When salient science is not enough to advance climate change adaptation: Lessons from Brazil and Australia Increased social and environmental vulnerability to extreme climatic events and inherent aggravation of environmental and social problems has placed climate change adaptation as an urgent challenge for decision-makers. Understanding and using climate change information to advance the implementation of climate-friendly policies further compounds this challenge. A rich scholarly literature focusing on climate change adaptation endorses that investing in mechanisms that narrow the gap between climate change information production and its use is crucial to increase adaptive capacity. Based on this assumption, this paper investigates the extent to which two collaborative projects that functioned as boundary organisations in Brazil (CiAdapta project) and Australia (Climate Change Adaptation for Natural Resource Management in East Coast Australia) increased access to information, and enabled the continual and continuous usefulness of produced knowledge for climate change adaptation. Considering the distinction between usable and useful information, we applied six criteria to guide the data analysis and extract key lessons from each project. Our findings confirm that face-to-face interactions are more likely to result in research having the societal impact that is being increasingly required by research and funding bodies. Our findings also indicate that two key systemic changes are critical for the long-term influence of boundary organisations for advancing climate change adaptation. These include changes to the science, knowledge production process; and shift in the political culture.

year: 2020

title: Maori & Psychology Research Unit annual report 2007

authors: Rua, Mohi

subjects: Maori and Psychology Research Unit

abstract: Annual report of the Maori and Psychology Research Unit (MPRU) 2007. The unit was established in August of 1997. The unit is designed to provide a catalyst and support network for enhancing research concerning the psychological needs, aspirations, and priorities of Maori people. The MPRU is well situated to draw together skilled and experienced interdisciplinary research groups by networking and establishing working relationships with staff and students within the Faculty of Arts and Social Sciences, the University, and the wider community.

text: Maori & Psychology Research Unit annual report 2007 Annual report of the Maori and Psychology Research Unit (MPRU) 2007. The unit was established in August of 1997. The unit is designed to provide a catalyst and support network for enhancing research concerning the psychological needs, aspirations, and priorities of Maori people. The MPRU is well situated to draw together skilled and experienced interdisciplinary research groups by networking and establishing working relationships with staff and students within the Faculty of Arts and Social Sciences, the University, and the wider community.

year: 2008