Prelude. Cycle 1. Introduction. Cycle 2. Structure defines function. Cycle 3. Diversity of cortical functions is provided by inhibition. Cycle 4. Windows on the brain. Cycle 5. A system of rhythms: from simple to complex dynamics. Cycle 6. Synchronization by oscillation. Cycle 7. The brain's default state: self-organized oscillations in rest and sleep. Cycle 8. Perturbation of the default patterns by experience. Cycle 9. The gamma buzz: gluing by oscillations in the waking brain. Cycle 10. Perceptions and actions are brain state-dependent. Cycle 11. Oscillations in the "other cortex:" navigation in real and memory space. Cycle 12. Coupling of systems by oscillations. Cycle 13. The tough problem. References.

Rhythms of the brain

A common assumption historically in ecology is evident in the term "balance of nature." The phrase usually implies that undisturbed nature is ordered and harmonius, and that ecological systems return to a previous equilibrium after disturbances. The more recent concepts of point equilibrium and static stability, which characterize the classical equilibrium paradigm in ecology, are traceable to the assumptions implicit in "balance of nature." The classical equilibrium view, however, has failed not only because equilibrium conditions are rare in nature, but also because of our past inability to incorporate heterogeneity and scale multiplicity into our quantitative expresssions for stability. The theories and models built around these equlibrium and stability principles have misrepresented the foundations of resource management, nature conservation, and environemtnal protection. In this paper, we sysntesize recent developments that advance our understandings of equilibrium vs. nonequilibrium, homogeneity vs....

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From balance of nature to hierarchical patch dynamics: A paradigm shift in ecology

Epistatic interactions, manifested in the effects of mutations on the phenotypes caused by other mutations, may help uncover the functional organization of complex biological networks. Here, we studied system-level epistatic interactions by computing growth phenotypes of all single and double knockouts of 890 metabolic genes in Saccharomyces cerevisiae, using the framework of flux balance analysis. A new scale for epistasis identified a distinctive trimodal distribution of these epistatic effects, allowing gene pairs to be classified as buffering, aggravating or noninteracting. We found that the ensuing epistatic interaction network could be organized hierarchically into function-enriched modules that interact with each other 'monochromatically' (i.e., with purely aggravating or purely buffering epistatic links). This property extends the concept of epistasis from single genes to functional units and provides a new definition of biological modularity, which emphasizes interactions between, rather than within, functional modules. Our approach can be used to infer functional gene modules from purely phenotypic epistasis measurements.

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Modular epistasis in yeast metabolism.

This paper identi"es challenges inherent in addressing multi-scale environmental problems, and outlines tentative guidelines for addressing such challenges and linking science and policy across scales. The study and practice of environmental assessment and management increasingly recognize the importance of scale and cross-scale dynamics in understanding and addressing global environmental change. These ongoing e!orts, however, lack a systematic way of thinking about and addressing the challenges involved in integrating science and policy across multiple scales, for example, in the design of policy-relevant, scienti"c assessments of problems such as climate change. These challenges include matching scales of biogeophysical systems with scales of management systems, avoiding scale discordance (matching the scale of the assessment with the scale of management), and accounting for cross-scale dynamics. In this paper we propose tentative guidelines for meeting such challenges for both assessors and decisionmakers: (1) utilize boundary organizations* institutions which serve to mediate between scientists and decision-makers, and between these actors at di!erent scales; (2) utilize scale-dependent comparative advantages * coordinating the allocation of resources, technical expertise, and decision-making authority to best capitalize on scale-speci"c capabilities; and (3) employ adaptive assessment and management strategies * constructing long-term, iterative, experiment-based processes of integrated assessment and management. ( 2000 Elsevier Science Ltd. All rights reserved.

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Linking global and local scales: designing dynamic assessment and management processes

Waddington's (1942) notion of canalization has been widely invoked in developmental psychology to conceptualize species-typical regularities in behavioral development as genetically determined. In contrast, a developmental systems view, such as the one described in the present article, sees the genes as only one component in a hierarchy of influences, all of which contribute to canalize behavioral development. A key issue is that genetic activity does not by itself produce finished traits; differentiation occurs as a consequence of events above as well as below the cellular level, necessarily involving factors in addition to genetic influences to canalize behavioral development. In exploring the possible experiential canalization of development, it was found that the mallard duck embryo's contact call plays a canalizing role in species-speci fic perceptual development {Gottlieb, 1991). Thus, normally occurring experience, in concert with genetic and other activities, can canalize behavioral development. The concept of canalization has been utilized in several different ways in the psychological literature. Canalization was originally put forward by Holt (1931) to call attention to prenatal conditioning as a factor in narrowing down the initially diffuse or random nature of motor activity in the embryo or fetus. Holt saw the motor activity of the fetus and the infant as becoming organized through spatial and temporal contiguity learning that narrowed down originally diffuse neural pathways to a definite neural reflex arc. Thus, for Holt, canalization referred to the development of specific sensorimotor pathways out of an original multiplicity of such pathways; it was a label to capture the developmental-behavioral phenomenon of progression from diffuse to ordered or organized motor activity, with contiguity conditioning as the experiential mechanism whereby organized motor activity was achieved. Although Holt's concept of neural reflex circles to account for the development of grasping in the fetus and infant was an ingenious example of his point of view, it has remained an entirely speculative theoretical solution of primarily historical interest. Subsequent empirical studies in behavioral embryology have kept open the possibility that motor movements in the embryo and fetus of some species are patterned from the start, whereas in other species they appear to be random (see reviews in Gottlieb, 1970; Hamburger, 1973; Oppenheim, 1974).

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Experiential Canalization of Behavioral Development: Theory.

PrefaceAn Introduction: Structure and Representation of the WorldThe Individual EntitySome Basics of Hierarchical StructureRepresenting a Dynamic System Hierarchically: The Basic Triadic SystemRepresenting a Dynamic System Hierarchically: The Nontransivity of Effects Across LevelsThe Explicit Elaboration of a Hierarchy of NatureOrganic Evolution and the Hierarchy of NatureOrganic Evolution: Its Origin and Hierarchy StructureAppendixGlossaryReferencesIndex

Stanley N. Salthe

Papers

Evolving Hierarchical Systems: Their Structure and Representation