On the interaction of gamma-rhythmic neuronal populations

Local gamma-band (~30-100Hz) oscillations in the brain, produced by feedback inhibition on a characteristic timescale, appear in multiple areas of the brain and are associated with a wide range of cognitive functions. Some regions producing gamma also receive gamma-rhythmic input, and the interaction and coordination of these rhythms has been hypothesized to serve various functional roles. This thesis consists of three stand-alone chapters, each of which considers the response of a gamma-rhythmic neuronal circuit to input in an analytical framework. In the first, we demonstrate that several related models of a gamma-generating circuit under periodic forcing are asymptotically drawn onto an attracting invariant torus due to the convergence of inhibition trajectories at spikes and the convergence of voltage trajectories during sustained inhibition, and therefore display a restricted range of dynamics. In the second, we show that a model of a gamma-generating circuit under forcing by square pulses cannot maintain multiple stably phase-locked solutions. In the third, we show that a separation of time scales of membrane potential dynamics and synaptic decay causes the gamma model to phase align its spiking such that periodic forcing pulses arrive under minimal inhibition. When two of these models are mutually coupled, the same effect causes excitatory pulses from the faster oscillator to arrive at the slower under minimal inhibition, while pulses from the slower to the faster arrive under maximal inhibition. We also show that such a time scale separation allows the model to respond sensitively to input pulse coherence to an extent that is not possible for a simple one-dimensional oscillator. We draw on a wide range of mathematical tools and structures including return maps, saltation matrices, contraction methods, phase response formalism, and singular perturbation theory in order to show that the neuronal mechanism of gamma oscillations is uniquely suited to reliably phase lock across brain regions and facilitate the selective transmission of information

Reading between the crimes: Online media’s representation of Aboriginal and Torres Strait Islander people’s interaction with the criminal justice system in post-apology Australia

Australian research confirms that Aboriginal and Torres Strait Islander people experience high levels of social inequality, racism and injustice. Evidence of discrimination and inequality is most obvious within the criminal justice system where they are seriously over-represented. The Australian news media plays a large part in reinforcing Aboriginal and Torres Strait Islander inequality, stereotypes and racist ideology within specific situations such as the Northern Territory Emergency Response and the Redfern riots. This study widens the scope from how the media reports a single criminal justice event to how the media reports Aboriginal and Torres Strait Islander people’s interaction with the criminal justice system. The study relies on Norman Fairclough’s (2003) theory of critical discourse analysis to analyse critically 25 Australian online news media articles featuring Aboriginal and Torres Strait Islander people. Specifically, the study applies Fairclough’s (2003) three assumptive categories (existential, propositional and value). It identifies discourse reinforcing dominance and inequality within those media articles and reveals two major findings. The first significant finding is the unwillingness of any article to challenge or question the power structures that reinforce or lead to Aboriginal and Torres Strait Islander inequality. The second major finding involves three ideologies within the text communicating racism and inequality: neo-colonial, neo-liberal assimilation and paternalistic ideologies. The concern is that although the twenty-five news media articles appear neutral, the critical analysis reveals racist ideologies being communicated and an unwillingness to challenge the power structures that create these. This position suggests that racism is not just a problem of a bygone era—it is a contemporary issue continuing at a deeper level nestled in the underlying assumptions and ideologies found within news media discourse. These findings would bring awareness to the media’s discursive practices and generate further discussion and research to address the discursive structures responsible for perpetuating the systemic harm to Aboriginal and Torres Strait Islander people

Checking in on the Chesapeake: Some Questions of Design

The Chesapeake Bay Program ( the CBP or Program ) has been widely celebrated as a model of collaborative management for large multijurisdictional watersheds and for ecosystem management more generally.\u27 In an article published six years ago, I joined in the celebration.2 But recent events warrant consideration of whether restructuring of the program is called for. In this essay, I consider whether greater centralization of decisionmaking for the Bay would address recent criticisms of the Program and better protect the public interest. After evaluating two alternative forms for the Program involving greater centralization, I conclude that major restructuring is not in order. The decentralized networked character of the Program carries with it the risk of failure, through inattention or misuse by its participants, but it also gives the Program an integrative capability particularly suited to the task of managing a complex and rapidly evolving human-natural system that is still only partially understood

Sustainable Watersheds

By any interpretation of sustainability, additional public and private investment should be made to protect and restore watersheds and their incorporated landscapes as sources of ecosystem services. This investment may require reducing current consumption but is justified because it will enhance the well being of the present generation and also enable future generations to enjoy a quality of life equal to our own

HIV-1 infection of microglial cells in a reconstituted humanized mouse model and identification of compounds that selectively reverse HIV latency.

Most studies of HIV latency focus on the peripheral population of resting memory T cells, but the brain also contains a distinct reservoir of HIV-infected cells in microglia, perivascular macrophages, and astrocytes. Studying HIV in the brain has been challenging, since live cells are difficult to recover from autopsy samples and primate models of SIV infection utilize viruses that are more myeloid-tropic than HIV due to the expression of Vpx. Development of a realistic small animal model would greatly advance studies of this important reservoir and permit definitive studies of HIV latency. When radiation or busulfan-conditioned, immune-deficient NSG mice are transplanted with human hematopoietic stem cells, human cells from the bone marrow enter the brain and differentiate to express microglia-specific markers. After infection with replication competent HIV, virus was detected in these bone marrow-derived human microglia. Studies of HIV latency in this model would be greatly enhanced by the development of compounds that can selectively reverse HIV latency in microglial cells. Our studies have identified members of the CoREST repression complex as key regulators of HIV latency in microglia in both rat and human microglial cell lines. The monoamine oxidase (MAO) and potential CoREST inhibitor, phenelzine, which is brain penetrant, was able to stimulate HIV production in human microglial cell lines and human glial cells recovered from the brains of HIV-infected humanized mice. The humanized mice we have developed therefore show great promise as a model system for the development of strategies aimed at defining and reducing the CNS reservoir

King v. Burwell and the Triumph of Selective Contextualism

King v. Burwell presented the question of whether the Patient Protection and Affordable Care Act of 2010 (ACA) authorizes the Internal Revenue Service (IRS) to issue tax credits for the purchase of health insurance through Exchanges established by the federal government. The King plaintiffs alleged an IRS rule purporting to authorize tax credits in federal Exchanges was unlawful because the text of the ACA expressly authorizes tax credits only in Exchanges “established by the State.” The Supreme Court conceded the plain meaning of the operative text, and that Congress defined “State” to exclude the federal government. The Court nevertheless disagreed with the plaintiffs, explaining that “the context and structure of the Act compel us to depart from what would otherwise be the most natural reading of the pertinent statutory phrase.” The Court reached its conclusion by disregarding portions of the ACA’s text and considering only selected elements of the ACA’s structure, context, and purpose. The King majority’s selective contextualism embraced an unexpressed congressional “plan” at the expense of the plan Congress actually enacted

King v. Burwell and the Triumph of Selective Contextualism

King v. Burwell presented the question of whether the Patient Protection and Affordable Care Act of 2010 (ACA) authorizes the Internal Revenue Service (IRS) to issue tax credits for the purchase of health insurance through Exchanges established by the federal government. The King plaintiffs alleged an IRS rule purporting to authorize tax credits in federal Exchanges was unlawful because the text of the ACA expressly authorizes tax credits only in Exchanges “established by the State.” The Supreme Court conceded the plain meaning of the operative text, and that Congress defined “State” to exclude the federal government. The Court nevertheless disagreed with the plaintiffs, explaining that “the context and structure of the Act compel us to depart from what would otherwise be the most natural reading of the pertinent statutory phrase.” The Court reached its conclusion by disregarding portions of the ACA’s text and considering only selected elements of the ACA’s structure, context, and purpose. The King majority’s selective contextualism embraced an unexpressed congressional “plan” at the expense of the plan Congress actually enacted

Taxation Without Representation: The Illegal IRS Rule to Expand Tax Credits Under the PPACA

The Patient Protection and Affordable Care Act (PPACA) provides tax credits and subsidies for the purchase of qualifying health insurance plans on state-run insurance exchanges. Contrary to expectations, many states are refusing or otherwise failing to create such exchanges. An Internal Revenue Service (IRS) rule purports to extend these tax credits and subsidies to the purchase of health insurance in federal exchanges created in states without exchanges of their own. This rule lacks statutory authority. The text, structure, and history of the Act show that tax credits and subsidies are not available in federally run exchanges. The IRS rule is contrary to congressional intent and cannot be justified on other legal grounds. Because the granting of tax credits can trigger the imposition of fines on millions of individuals and employers, the IRS rule is likely to be challenged in court

Neurosystems: brain rhythms and cognitive processing

Neuronal rhythms are ubiquitous features of brain dynamics, and are highly correlated with cognitive processing. However, the relationship between the physiological mechanisms producing these rhythms and the functions associated with the rhythms remains mysterious. This article investigates the contributions of rhythms to basic cognitive computations (such as filtering signals by coherence and/or frequency) and to major cognitive functions (such as attention and multi-modal coordination). We offer support to the premise that the physiology underlying brain rhythms plays an essential role in how these rhythms facilitate some cognitive operations.098352 - Wellcome Trust; 5R01NS067199 - NINDS NIH HH