title: Toward a theory of the general-anesthetic-induced phase transition of the cerebral cortex. I. A thermodynamics analogy

authors: Steyn-Ross, Moira L.

subjects: thermodynamics

abstract: In a recent paper the authors developed a stochastic model for the response of the cerebral cortex to a general anesthetic agent. The model predicted that there would be an anesthetic-induced phase change at the point of transition into unconsciousness, manifested as a divergence in the electroencephalogram spectral power, and a change in spectral energy distribution from being relatively broadband in the conscious state to being strongly biased towards much lower frequencies in the unconscious state. Both predictions have been verified in recent clinical measurements. In the present paper we extend the model by calculating the equilibrium distribution function for the cortex, allowing us to establish a correspondence between the cortical phase transition and the more familiar thermodynamic phase transitions. This correspondence is achieved by first identifying a cortical free energy function, then by postulating that there exists an inverse relationship between an anesthetic effect and a quantity we define as cortical excitability, which plays a role analogous to temperature in thermodynamic phase transitions. We follow standard thermodynamic theory to compute a cortical entropy and a cortical “heat capacity,” and we investigate how these will vary with anesthetic concentration. The significant result is the prediction that the entropy will decrease discontinuously at the moment of induction into unconsciousness, concomitant with a release of “latent heat” which should manifest as a divergence in the analogous heat capacity. There is clear clinical evidence of heat capacity divergence in historical anesthetic-effect measurements performed in 1977 by Stullken et al. [Anesthesiology 46, 28 (1977)]. The discontinuous step change in cortical entropy suggests that the cortical phase transition is analogous to a first-order thermodynamic transition in which the comatose-quiescent state is strongly ordered, while the active cortical state is relatively disordered.

text: Toward a theory of the general-anesthetic-induced phase transition of the cerebral cortex. I. A thermodynamics analogy In a recent paper the authors developed a stochastic model for the response of the cerebral cortex to a general anesthetic agent. The model predicted that there would be an anesthetic-induced phase change at the point of transition into unconsciousness, manifested as a divergence in the electroencephalogram spectral power, and a change in spectral energy distribution from being relatively broadband in the conscious state to being strongly biased towards much lower frequencies in the unconscious state. Both predictions have been verified in recent clinical measurements. In the present paper we extend the model by calculating the equilibrium distribution function for the cortex, allowing us to establish a correspondence between the cortical phase transition and the more familiar thermodynamic phase transitions. This correspondence is achieved by first identifying a cortical free energy function, then by postulating that there exists an inverse relationship between an anesthetic effect and a quantity we define as cortical excitability, which plays a role analogous to temperature in thermodynamic phase transitions. We follow standard thermodynamic theory to compute a cortical entropy and a cortical “heat capacity,” and we investigate how these will vary with anesthetic concentration. The significant result is the prediction that the entropy will decrease discontinuously at the moment of induction into unconsciousness, concomitant with a release of “latent heat” which should manifest as a divergence in the analogous heat capacity. There is clear clinical evidence of heat capacity divergence in historical anesthetic-effect measurements performed in 1977 by Stullken et al. [Anesthesiology 46, 28 (1977)]. The discontinuous step change in cortical entropy suggests that the cortical phase transition is analogous to a first-order thermodynamic transition in which the comatose-quiescent state is strongly ordered, while the active cortical state is relatively disordered.

year: 2001

title: Sentence initial lexical bundles in Chinese and New Zealand PhD theses in the discipline of General and Applied Linguistics

authors: Li, Liang

abstract: Lexical bundles are recurrent multiword combinations and often function as discourse building blocks. Lexical bundles have been analysed in university students’ writing to detect linguistic errors, measure writing competence, and investigate the divergence between L1 and L2 writing. Few studies, however, have focused on the high-stakes genre of PhD thesis and investigated the bundle productions of the same genre within the same level and discipline. This paper compares sentence initial lexical bundles in the corpora of English theses written by Chinese and New Zealand PhD students in the discipline of General and Applied Linguistics. Forty-six bundles from a Chinese corpus and forty-two bundles from a New Zealand corpus were generated. Among them, 94% of sentence initial bundles were identified as metadiscursive bundles. Chinese and New Zealand doctoral students showed considerably different preferences in their bundle selection. The paper examines the possible impact of these preferences and suggests there is a need to extend the metadiscourse knowledge of doctoral students in terms of lexical bundles.

text: Sentence initial lexical bundles in Chinese and New Zealand PhD theses in the discipline of General and Applied Linguistics Lexical bundles are recurrent multiword combinations and often function as discourse building blocks. Lexical bundles have been analysed in university students’ writing to detect linguistic errors, measure writing competence, and investigate the divergence between L1 and L2 writing. Few studies, however, have focused on the high-stakes genre of PhD thesis and investigated the bundle productions of the same genre within the same level and discipline. This paper compares sentence initial lexical bundles in the corpora of English theses written by Chinese and New Zealand PhD students in the discipline of General and Applied Linguistics. Forty-six bundles from a Chinese corpus and forty-two bundles from a New Zealand corpus were generated. Among them, 94% of sentence initial bundles were identified as metadiscursive bundles. Chinese and New Zealand doctoral students showed considerably different preferences in their bundle selection. The paper examines the possible impact of these preferences and suggests there is a need to extend the metadiscourse knowledge of doctoral students in terms of lexical bundles.

year: 2022-09-21

title: WERO: A pānui for tauira Māori in psychology

authors: Waitoki, Waikaremoana

abstract: The first WERO pānui was edited in 1991 by the first Māori in psychology at Waikato University, Stephanie Palmer and Linda Waimarie Nikora. This pānui is the third in the WERO series, aiming to continue the legacy of the first publication in 1991 (edited by Stephanie Palmer) and the second in 1992 (edited by Hikitapua). The pānui continues to center diverse Māori perspectives with relevance for those affected by racial oppression in psychology.

text: WERO: A pānui for tauira Māori in psychology The first WERO pānui was edited in 1991 by the first Māori in psychology at Waikato University, Stephanie Palmer and Linda Waimarie Nikora. This pānui is the third in the WERO series, aiming to continue the legacy of the first publication in 1991 (edited by Stephanie Palmer) and the second in 1992 (edited by Hikitapua). The pānui continues to center diverse Māori perspectives with relevance for those affected by racial oppression in psychology.

year: 2024-06-03