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PubMed2003

A critical evaluation of the force control hypothesis in motor control.

The ability to formulate explicit mathematical models of motor systems has played a central role in recent progress in motor control research. As a result of these modeling efforts and in particular the incorporation of concepts drawn from control systems theory, ideas about motor control have changed substantially. There is growing emphasis on motor learning and particularly on predictive or anticipatory aspects of control that are related to the neural representation of dynamics. Two ideas have become increasingly prominent in mathematical modeling of motor function--forward internal models and inverse dynamics. The notion of forward internal models which has drawn from work in adaptive control arises from the recognition that the nervous system takes account of dynamics in motion planning. Inverse dynamics, a complementary way of adjusting control signals to deal with dynamics, has proved a simple means to establish the joint torques necessary to produce desired movements. In this paper, we review the force control formulation in which inverse dynamics and forward internal models play a central role. We present evidence in its favor and describe its limitations. We note that inverse dynamics and forward models are potential solutions to general problems in motor control--how the nervous system establishes a mapping between desired movements and associated control signals, and how control signals are adjusted in the context of motor learning, dynamics and loads. However, we find little empirical evidence that specifically supports the inverse dynamics or forward internal model proposals per se. We further conclude that the central idea of the force control hypothesis--that control levels operate through the central specification of forces--is flawed. This is specifically evident in the context of attempts to incorporate physiologically realistic muscle and reflex mechanisms into the force control model. In particular, the formulation offers no means to shift between postures without triggering resistance due to postural stabilizing mechanisms.

Animals↗

PubMed1981

Teaching the family system concept in family medicine.

Teaching the family system concept to physicians is difficult, as it entails a new way of thinking, at odds with the familiar linear medical model that focuses on the individual patient. This conceptual difference and the confusion between working with families in family medicine and family therapy explain the slow or superficial acceptance of family as the unit of care. Five principles have been found to be useful in teaching: (1) specific teaching techniques should take into account previous training and current time constraints; (2) evidence for the relevance of system theory to diagnosis, treatment, and prevention should be evaluated early in the teaching program; (3) clarity of expectations is crucial; (4) emphasis should be on the natural role of the family physician as first-line family advisor and the use of interviewing and observational skills already well developed; and (5) synthesis of the psychosocial and physical aspects of illness will occur naturally if the family physician is the teacher of family system concepts and the role model for their application in practice.

Adult↗

PubMed2006

Time scale and dimension analysis of a budding yeast cell cycle model.

BACKGROUND: The progress through the eukaryotic cell division cycle is driven by an underlying molecular regulatory network. Cell cycle progression can be considered as a series of irreversible transitions from one steady state to another in the correct order. Although this view has been put forward some time ago, it has not been quantitatively proven yet. Bifurcation analysis of a model for the budding yeast cell cycle has identified only two different steady states (one for G1 and one for mitosis) using cell mass as a bifurcation parameter. By analyzing the same model, using different methods of dynamical systems theory, we provide evidence for transitions among several different steady states during the budding yeast cell cycle. RESULTS: By calculating the eigenvalues of the Jacobian of kinetic differential equations we have determined the stability of the cell cycle trajectories of the Chen model. Based on the sign of the real part of the eigenvalues, the cell cycle can be divided into excitation and relaxation periods. During an excitation period, the cell cycle control system leaves a formerly stable steady state and, accordingly, excitation periods can be associated with irreversible cell cycle transitions like START, entry into mitosis and exit from mitosis. During relaxation periods, the control system asymptotically approaches the new steady state. We also show that the dynamical dimension of the Chen's model fluctuates by increasing during excitation periods followed by decrease during relaxation periods. In each relaxation period the dynamical dimension of the model drops to one, indicating a period where kinetic processes are in steady state and all concentration changes are driven by the increase of cytoplasmic growth. CONCLUSION: We apply two numerical methods, which have not been used to analyze biological control systems. These methods are more sensitive than the bifurcation analysis used before because they identify those transitions between steady states that are not controlled by a bifurcation parameter (e.g. cell mass). Therefore by applying these tools for a cell cycle control model, we provide a deeper understanding of the dynamical transitions in the underlying molecular network.

Cell Cycle↗

PubMed1992

Geometrical techniques for analyzing ECG dynamics.

Nonlinear dynamical systems theory motivates a new class of techniques for analyzing signals, based on the idea of converting a signal into a geometrical object--a "trajectory" in a reconstructed "state space." This paper discusses one such technique for detecting and quantifying electrical alternans.

Electrocardiography↗

PubMed1979

Human eye tracking as a sequential input adaptive process.

Sequential input adaptive system theory is applied to human eye tracking of targets with one-dimensional motion defined by since functions, sums of sine functions and triangle functions. The sequential theory describes the mean eye tracking movements of two subjects for these inputs. The theory is predictive for irregular inputs in that when its parameters for a subject are identified and adjusted for a reference input, it then predicts mean eye tracking behavior for that subject for inputs of comparable complexity.

Eye Movements↗

PubMed2006

Theoretical analysis of high-resolution digital mammography.

The performance of a high-resolution charge coupled device-based full-field digital mammography imager was analysed using a mathematical framework based on an adaptation of cascaded linear systems theory described by other investigators. This work has been conducted in order to understand the impact of various design parameters on the physical performance characteristics of the imager. Specifically, the effect of pixel size, scintillator thickness and packing density, x-ray spectra, air kerma, dark current, charge integration time, and pixel fill-factor on the frequency dependent detective quantum efficiency was studied using a charge-coupled device as a reference platform. The imaging system was modelled as a series of physical processes with gain and spatial spreading. For each stage, the signal and noise power spectra were computed and propagated through the imaging chain as inputs to subsequent stages. Good agreement between experimental and theoretical predictions was obtained for various x-ray spectral conditions that were investigated. The modulation transfer function, MTF(f) and detective quantum efficiency DQE(f) characteristics obtained in this study are encouraging and comparable to other digital mammography systems. The results of this study strongly suggest the feasibility of large area scintillator-based digital mammography imagers with pixel sizes below 100 microm.

Algorithms↗

PubMedDate not supplied

[Restless children. An exercise in epistemic confusion].

Drawing on systemic thinking (i.e. constructivist systems theory) the paper reviews grossly the assumptions underlying childhood's restlessness ("hyperactivity") both as a distinct nosological entity and as foundation for different treatments. The phenomenon is considered, in accordance with contemporary ideas, as an interactional one. Two case examples serve as a starting point for gathering basic elements which, if put together, allow to understand this phenomenon without falling into the extremes of a mainly medical or a socionormative approach. This permits to make use of the systemic view in a manner that enables the therapist to adopt an attitude of respectful acceptance and understanding towards his/her small clients and their relatives.

Aggression↗

PubMed1982

The family circle method for integrating family systems concepts in family medicine.

The family circle method is a process that allows individuals to draw a schematic diagram of their family system. It is closely allied with family systems theory and family medicine philosophy. The method is readily understandable with brief instructions. Individuals can create a family circle drawing in as little as two or three minutes. Once instructions are given, the presence of the physician is not required during the drawing. Family circle drawings will often illustrate, in graphic form, patterns of closeness and distance, of power and decision making, of family alliances and boundaries. The drawings provide at a glance an overview of the family system as seen by the person who does the drawing. The drawings are a rich source of information concerning family dynamics and are useful for setting goals for changes in the family system.

Adolescent↗

PubMed1987

Accuracy of alternative representations for integrated biochemical systems.

The Michaelis-Menten formalism often provides appropriate representations of individual enzyme-catalyzed reactions in vitro but is not well suited for the mathematical analysis of complex biochemical networks. Mathematically tractable alternatives are the linear formalism and the power-law formalism. Within the power-law formalism there are alternative ways to represent biochemical processes, depending upon the degree to which fluxes and concentrations are aggregated. Two of the most relevant variants for dealing with biochemical pathways are treated in this paper. In one variant, aggregation leads to a rate law for each enzyme-catalyzed reaction, which is then represented by a power-law function. In the other, aggregation produces a composite rate law for either net rate of increase or net rate of decrease of each system constituent; the composite rate laws are then represented by a power-law function. The first variant is the mathematical basis for a method of biochemical analysis called metabolic control, the latter for biochemical systems theory. We compare the accuracy of the linear and of the two power-law representations for networks of biochemical reactions governed by Michaelis-Menten and Hill kinetics. Michaelis-Menten kinetics are always represented more accurately by power-law than by linear functions. Hill kinetics are in most cases best modeled by power-law functions, but in some cases linear functions are best. Aggregation into composite rate laws for net increase or net decrease of each system constituent almost always improves the accuracy of the power-law representation. The improvement in accuracy is one of several factors that contribute to the wide range of validity of this power-law representation. Other contributing factors that are discussed include the nonlinear character of the power-law formalism, homeostatic regulatory mechanisms in living systems, and simplification of rate laws by regulatory mechanisms in vivo.

Biochemistry↗

PubMed1989

Theory development in perspective: the role of conceptual frameworks and models in theory development.

An analysis of most scientific theories reveals the presence of a variety of components which function as constitutive elements of theories. Wider cultural paradigms often influence the construction and content of theories in a decisive way. Analogies between incongruent domains provide significant points of departure for the development of models which are often metaphoric in nature. Different metaphors provide alternative conceptual frameworks in terms of which it is possible to describe and explain nursing phenomena. Scientific theories that are developed on the basis of such metaphorical models are limited in their explanatory capacity. When the intrinsic limitations of such scientific models are not recognized, they often lead to distorted, one-sided and reductionistic explanations of phenomena. Metaphysical assumptions concerning the nature of human beings, illness, health, etc., are also of decisive significance in this process, e.g. mechanistic models based on a naturalistic view of man lead theorizing astray. These theses are illustrated with reference to behavioral systems theory as developed by Dorothy Rogers.

Holistic Health↗

PubMed2002

Observing mother-child relationships across generations: boundary patterns, attachment, and the transmission of caregiving.

Grounded in both attachment and family systems theories, this study is one of the first to examine how relationship patterns observed in mothers' current relationships with their own mothers are recreated in their relationships with their infants. Mostly white, middle-class families (N = 55), including maternal grandmothers, mothers, and infants, were observed when infants were 6, 9, and 18 months old. At 6 months, mothers and grandmothers completed self-report assessments and worked together on discussion tasks. These interactions were coded using the Boundary Assessment Coding System, developed for the present study, which assessed three relational patterns: disengagement, balance, and entanglement. At 9 months, mothers were rated on sensitivity and intrusiveness while playing with and feeding their infants; and, at 18 months, infant-mother attachment was assessed using the Strange Situation. Multiple regression analyses revealed, as predicted, that mothers who remembered being accepted by their mothers as children and who were in highly balanced relationships with their own mothers currently were more sensitive and less intrusive with their 9-month-old infants. Further, discriminant function analyses indicated that memories of acceptance, high levels of balance, and low levels of disengagement differentiated secure from insecure attachment, whereas memories of overprotection and high levels of entanglement distinguished resistant from secure and avoidant attachment. Discussion focuses on the theoretical hypothesis that mothers internalize relationship strategies experienced with their own caregivers and recreate these patterns with their infants.

Adult↗

PubMed1996

[Autoregulation in therapeutic effects].

Self-regulation as the basic principle in the organization of living beings is analyzed from the viewpoint of the functional system theory for orthodox medicine and nonconventional therapies. Only some therapies in orthodox medicine are based on self-regulation whereas its role in nonconventional or traditional medicine is proposed to be more frequent and important. The paper describes how the similar principle can be clearly understood when the fundamental FST-principle (self-regulation) is used. The problems of the so-called vibrational medicine with its notion of a human being as a multidimensional organism made up of physical/cellular systems in a dynamic interplay with complex regulatory energy fields. Self-regulation is considered to be the crucial principle when subtle energetic medical approaches are applied as a cure. The paper also draws attention to informational processes in the body and its possible role in the mechanisms of orthodox and nonconventional therapies. The idea that the methods of traditional medicine have to be considered as complementary, but not alternative to orthodox, academic medicine is emphasized.

Complementary Therapies↗

PubMed1988

Changing perceptions of family cohesion and power across adolescence.

Adolescents' perceptions of family relationships were studied using the FAST, a spatial technique in which wooden figures were placed on a board to represent cohesion and power. 150 subjects, drawn equally from sixth, ninth, and twelfth grades, portrayed the family in 2 representations: as perceived typically and ideally. Father-mother, father-child, and mother-child dyads were analyzed. Perceptions were strongly influenced by age, type of representation, and dyad. In accord with a developmental perspective, older adolescents portrayed less cohesion in parent-child dyads and smaller power differences in all dyads than did younger adolescents. In accord with family systems theory, the father-mother dyad was depicted as the most cohesive and as near egalitarian in power. At all ages and in both representations, parents were perceived as more powerful than their children. The family was generally portrayed as cohesive, significantly more so in the ideal than typical representation. Furthermore, in the ideal representation there were no significant power differences between the parents but moderate power differences in the parent-child dyads. Results were interpreted from both developmental and family systems perspectives.

Adolescent↗

PubMed1999

Schizophrenia: orthodoxy and heresies. A review of alternative possibilities.

Conflicts about the nature, causes and treatment of schizophrenia have never ceased. Recently, however, a particular set of beliefs ('the Orthodoxy') has become influential, and dominates political and managerial agenda for controlling clinical practice and educational initiatives. Theories and therapeutic strategies that differ from the particular biological, behavioural, cognitive and family management approaches favoured by orthodox clinicians have been given far less academic and clinical air-space. This review surveys some alternative ideas and practices ('the Heresies') and critically refers to some of the orthodox tenets such as the genetic and biological bases of schizophrenia, the disease model, 'family blaming' and drug treatment. Heresies briefly explored include schizophrenia as an evolutionary inevitability, creative sublimation of schizotypal tendencies and systems-theory-based family therapies.

Attitude to Health↗

PubMed1994

Systemic lupus erythematosus: theories of pathogenesis and approach to therapy.

Human systemic lupus is a heterogeneous disorder characterized by multisystem inflammatory disease and the production of a variety of autoantibodies. For many years, in our ignorance, we had the freedom to imagine numerous abnormalities which might give rise to lupus: defects of the immune system, viruses, major histocompatibility driven predispositions, complement or complement receptor defects, biochemical abnormalities, impaired DNA repair, sex hormone imbalances, and many others. Now, the basis for lupus in lpr/lpr mice has been uncovered: a mutation in fas. The normal Fas cell surface molecule is important in programmed cell death, apoptosis. The lpr-associated defect in Fas interferes with normal apoptosis, allowing persistence of self-reactive lymphocytes. This finding is especially exciting to those of us who have stressed lupus-associated defects in tolerance. It also illustrates the apparent antigen-nonspecific nature of an etiologic abnormality leading to lupus. The multigenic NZB disorder is less well dissected. Recent work points to defects in an unusual bone marrow progenitor population. Patients with systemic lupus erythematosus may have different and multiple pathogenic factors, including those listed above. We recently have found that some patients with lupus have persistence of T cells with random mutations, consistent with prior abnormal activation and, perhaps, impaired apoptosis. Future therapies of patients must consider both the heterogeneity and the multifactorial pathogenesis of the syndrome we call "lupus."

Animals↗

PubMed2000

Towards a control model for the highly cybernetic farming ecosystems.

A dynamic model based on the linear systems theory is developed in designing a highly cybernetic farming strategy to efficiently manage residuals generated in farm ecosystems. A linear cybemetic model would be used to describe the dynamic behavior of resource flow in the farm ecosystem in which the state variables are resource quantities, and the control variables are residual quantities. The controlled process is defined as the controlled management strategy change. Cybemetic mechanism shows the application of residuals as control measures have determinate effects on the controlled process as along as the farming system is observable and controllable in the control sense. To illustrate the model algorithm the idea is applied to simulate the dynamic response of residual phosphorus concentrations in an integrated pig/corn farming system located in the south Taiwan region. General results show that the residual phosphorous concentration is influenced by farming activities which are controlled by a system of gross input and net output parameters. This paper demonstrates using input-output analysis technique that residuals generated in the farming system is the most important cybemetic variable,

Agriculture↗

PubMedDate not supplied

[Philosophical aspects of the theory of adaptation].

This paper discusses the general concepts of the problem of adaptation from the dialectic point of view which, according to F. Engels, is the most important pattern of thinking in natural sciences. Dialectics provides an analog and therefore a method for interpreting developmental processes, universal relationships in nature, transition from one area of research to another. From the point of view of dialectic laws adaptation acts as a contradictory process of habituation to various environments. The contradictory pattern of the adaptive process and its result is very distinct in terms of heredity and variability. A logical enlargement of the concept of adaptation is the transition to the study of homeostasis which is assumed to be its mechanism, a property which has developed in the course of evolution and fixed in heredity. This adaptive property is contradictory in its essence because homeostasis is a unity of stability and instability, a fluctuating constancy. In addition to the law of constancy of the inner melieu, there is a law of homeostatic deviations. This concept can be understood through an analysis of the system theory that includes a continuous variation and conservation of structure which indicates its ordered oscillation, that is, its rhythmicity. This clarifies the relationship between homeostasis and biological rhythmicity as a method of maintaining the former. Thus, a consistent analysis of the problem of adaptation can help identify transition from one area of research to another, specifically to the study of oscillatory processes in living systems, including such oscillatory processes that have characteristics of universality and necessity. Such processes are biological rhythms with a period of about 24 hours, that is, circadian rhythms.

Adaptation, Biological↗

PubMed1993

Systems analysis of an occupational health department: recommendations to increase effectiveness.

The author analyzes the occupational health department of an urban health maintenance organization using systems theory. The framework for the analysis includes the environment, inputs, throughputs, outputs, evaluation, and forces of entropy and negentropy, as well as stresses and strains. Recommendations to increase the effectiveness of the department are based on the analysis. Any occupational health department could benefit from a similar analysis.

Efficiency↗