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At least 811 records · Page 45Linked to original sources
PubMed1998

Epilepsy, vagal nerve stimulation by the NCP system, mortality, and sudden, unexpected, unexplained death.

PURPOSE: To determine rates of all-cause mortality and of sudden, unexpected, unexplained deaths in epilepsy (SUDEP) in a cohort of individuals treated with the Neuro Cybernetic Prosthesis (NCP) System for intractable epilepsy, and; to contrast the NCP experience with other epilepsy cohorts. METHODS: A cohort of 791 individuals were followed for 1,335 person-years from implantation. Of the total cohort, 120 individuals had their NCP System devices deactivated. The 15 deaths which occurred during NCP System activation were reviewed for SUDEP by a panel. There were three additional deaths and 242.5 person-years of monitoring after deactivation. RESULTS: The standardized mortality ratios for NCP System were 5.3, 95% confidence interval (CI) 3.0-8.7; and for the time period after device deactivation, 4.4, 95% CI 0.9-12.8. Six of the deaths during stimulation were considered definite or probable SUDEP and two as possible SUDEP. Seven were not considered to be SUDEP. The incidence of definite/probable SUDEP was 4.5 per 1,000 person-years and 6.0 per 1,000 person-years for definite/probable/possible SUDEP. CONCLUSIONS: The mortality rates and standardized mortality ratios are comparable with studies of young adults with intractable epilepsy who were not treated with NCP System. These SUDEP rates are not significantly different from those reported in the recent studies of lamotrigine (LTG), gabapentin (GBP), and tiagabine (TGB). The higher rates of SUDEP in the NCP System cohort, as compared with recent drug trials, presumably is explained by the selection of relatively higher-risk patients for the NCP System device.

Adult↗
PubMed2001

Factors influencing optical 3D scanning of vinyl polysiloxane impression materials.

PURPOSE: Future growth in dental practice lies in digital imaging enhancing many chairside procedures and functions. This revolution requires the fast, accurate, and 3D digitizing of clinical records. One such clinical record is the chairside impression. This study investigated how surface angle and surface roughness affect the digitizing of vinyl polysiloxane impression materials. MATERIALS AND METHODS: Seventeen vinyl polysiloxane impression materials were digitized with a white light optical digitizing system. Each sample was digitized at 3 different angles: 0 degrees, 22.5 degrees, and 45 degrees, and 2 digitizer camera f-stops. The digitized images were rendered on a computer monitor using custom software developed under NIH/NIDCR grant DE12225. All the 3D images were rotated to the 0 degrees position, cropped using Corel Photo-Paint 8 (Corel Corp, Ottawa, Ontario, Canada), then saved in the TIFF file format. The impression material area that was successfully digitized was calculated as a percentage of the total sample area, using Optimas 5.22 image processing software (Media Cybernetics, LP, Silver Spring, MD). The dependent variable was a Performance Value calculated for each material by averaging the percentage of area that digitized over the 3 angles. New samples with smooth and rough surfaces were made using the 7 impression materials with the largest Performance Values. These samples were tested as before, but with the additional angle of 60 degrees. Silky-Rock die stone (Whip Mix Corp, Louisville, KY) was used as a control. RESULTS: The Performance Values for the 17 impression materials ranged from 0% to 100%. The Performance Values for the 7 best materials were equivalent to the control at f/11 out to a surface angle of 45 degrees; however, only Examix impression material (GC America Inc, Alsip, IL) was equivalent to the control at f/11/\16. At the 60 degrees surface angle with f/11/\16, the Performance Values were 0% for all the impression materials, whereas that for the control was 90%. The difference in the Performance Values for the smooth and rough surface textures was 7%, which was not significant. CONCLUSIONS: The digitizing performance of vinyl polysiloxane impression materials is highly material and surface angle-dependent and is significantly lower than the die stone control when angles to 60 degrees are included. It is affected to a lesser extent by surface texture.

Analysis of Variance↗
PubMed1994

The role of modulated gap junctional intercellular communication in epigenetic toxicology.

The normal development and health of all multicellular organisms, including the human being, depend on the adaptive maintenance of the integrity of the genetic information (e.g., DNA protective and repair mechanisms), as well as of the homeostatic and cybernetic regulatory systems within and between tissues. The primary focus of the past and current toxicological studies and risk assessment practices has been to ascertain and predict the "genotoxicity" of various physical and chemical agents. The paradigm of "carcinogen as mutagen," while valuable for stimulating studies of the detection of mutagens and of their potential role in "causing" somatic and germ line diseases, has tended to blunt research on the role of nongenotoxic mechanisms in disease causation. This brief analysis will emphasize the need to consider the role of modulated gap junctional intercellular communication (GJIC) in any biological risk assessment model. It is based on the following assumptions and facts. Because gap junctions exist in all metazoans, they have been associated with the regulation of cell proliferation, development, differentiation, and the adaptive function of both excitable and nonexcitable coupled cells. A highly evolutionarily conserved family of genes codes for proteins (connexins), which, as hexameric units (connexons), form membrane-associated channels of gap junctions. Cells coupled by gap junctions will have their ions and small regulatory molecules equilibrated. Regulation of GJIC can be at the transcriptional, translational, or posttranslational levels. Transient down or up regulation of GJIC can be induced by endogenous or exogenous chemicals via many mechanisms at any of these three levels. Stable abnormal regulation has been associated with activated oncogenes, and normal regulation has been associated with several tumor suppressor genes. The dysfunction of these gap junctions might play a role in the actions of various toxic chemicals that have cell type/tissue/organ specificity. This could bring about distinct clinical consequences, such as embryo lethality or teratogenesis, reproductive dysfunction in the gonads, neurotoxicity of the central nervous system, hyperplasia of the skin, and tumor promotion of initiated tissue. Modulation of GJIC should be viewed as a scientific basis of "epigenetic toxicology" because the alteration of intercellular communication would alter the internal physiological state of the cell. The inhibition of GJIC is a necessary component of mitogenesis (a necessary component of the multistage carcinogenic process). The modulation of GJIC can have both toxicological, as well as therapeutic potential.

Animals↗
PubMed1986

Sequences: toward a common denominator of family therapy.

This paper presents a conceptual framework that is designed to help clinicians and researchers organize their observations of the complex network of interconnected sequences of behavior and thinking that constitute family interactions. This framework distinguishes four classes of recursive sequences, each of which is defined by its period, i.e., the amount of time it takes for a sequence to complete one cycle. The shortest sequences (S1) are those face-to-face interaction patterns that range in length from seconds to an hour. S2 sequences are played out over one day to one week, often depending on the routines of the family. S3 sequences range from several weeks to a year, and S4 sequences are those patterns of interaction and thought that repeat from generation to generation. In addition to outlining this framework, the paper contends that in many families with a problem, pertinent sequences from each class may be related to the problem and to each other in a cybernetic manner. Suggestions are offered for identifying pertinent sequences from each class and for selecting interventions that best address the targeted sequence. We have found that this conceptual framework has enabled us to use techniques from many different schools of family therapy while avoiding the conceptual contradictions inherent in previous attempts to integrate approaches.

Adolescent↗
PubMed1990

Reflections during a study on family therapy with drug addicts.

This article presents ideas and reflections emerging during a project on family therapy with drug abusers. Initially inspired by the writings of Stanton and Todd on the subject, the project developed into a recursive and self-reflective process, characterized by increasing doubts about the usefulness of categorization of families, of pre-planning therapy, and of the therapist as an "expert." The limitations of approaches that emphasize the importance of understanding the family structure as the basis for changing it are discussed, particularly with respect to how they decrease therapist flexibility and may block the family's finding their own solution. Alternative approaches to practice and research are also discussed, bearing on ideas particularly formulated by theoreticians and practitioners inspired by second-order cybernetics.

Adolescent↗
PubMed1994

Using a narrative metaphor: implications for theory and clinical practice.

The evolution of family therapy from a cybernetic metaphor to a narrative metaphor has led us to think differently about therapy, about clients, and about ourselves as therapists. In this article we pursue how this different way of thinking has informed a theoretical understanding of a narrative therapy approach and consequently has opened space for different ways of working clinically. We begin by tracing the evolution to narrative; we consider the implications of social constructionism and its political effects; and we complete the discussion by focusing on narrative theory. We then show how the clinical work follows logically and is coherent with the theoretical considerations. We describe, and illustrate with clinical examples, an innovative approach to working with couples and families with adolescents. In this work we pay attention to the larger cultural stories, including gender constructions, and to personal stories that persons have created to make meaning out of their experience as they interact with one another in a reciprocal meaning-making process. Interventions focus on externalizing the problem narrative that is influencing the client(s), mapping the effects of the problem pattern and/or the totalizing view persons might have of others, and creating space for client(s) to notice preferred actions and intentions. Finally, we close the loop by asking questions of ourselves and others about the effects of working from a narrative metaphor.

Adolescent↗
PubMed1977

Group models, group dynamics, sociological and psychological aspects of group formation and evaluation.

Several group models are defined: a mechanistic model, a model of conflicts, a cybernetic model, a field-theoretical model, an organismic model, an interactionistic model. In all these models the group is a dynamic entity which is based on a mutual dependence of the members. From this sociological-horizontal-interactional point of view the group is therefore an entity. From a psychological-vertical aspect the group is rather a common situation in which the individual members remain in their experience separated from each other. To understand the group therapeutic dynamics it is necessary to keep in mind these two levels. From the sociological aspect, e.g. the frequency and kinds of interactions, the relationship of the inside-distances between the members to the distances of the members to the outside is decisive for group cohesion. The more the total interaction in a group augments, the more the emotionally loaded interactions increase. The significance of group cohesion in the therapeutic process is documented also by means of standardized rating scales. The normative effect of the group, the different roles in it, the group structure have to be considered if the group is to be used as a therapeutic mean. From the psychological point of view five phases of group development can be differentiated: 1) explorative contact, 2) regression, 3) catharsis, 4) insight, 5) social learning. By a factor analysis Lieberman et al. have found out that independent of the method used, the following types of group leaders were successful: the "provider", the "social engineer", the "energizer".

Group Processes↗
PubMed1988

Adrenocorticotropic hormone in the control of renal tubular hydrogen ion secretion. Balance of non-metabolizable base in ACTH-stimulated weanling rats subject to acid or base loading.

Groups of weanling rats subject to ACTH-stimulation (tetracosactrin, 1 mg kg-1 day-1) were exposed to heavy oral loads of ammonium chloride (approx. 21 mmol kg-1 day-1) or sodium bicarbonate (approx. 40 mmol kg-1 day-1) for 8 days. During loading with sodium bicarbonate, the animals maintained a normal positive external (whole body) balance of non-metabolizable base (NB), excess NB being excreted quantitatively in the urine, whereas loading with ammonium chloride caused a fall in the mean balance of NB from a reference value of 12.1 mmol per 8 days to about zero. However, in the two groups the concentration in plasma of NB rose from the reference value (41 mmol l-1) to the same level (57 and 59 mmol l-1, respectively; P greater than 0.5) despite extreme differences in rates of gastrointestinal NB absorption, despite a significant rise in the rate of endogenous sulphuric acid production and despite the presence of ample chloride in diet and urine. These results indicate that ACTH determines the extracellular concentration of NB at which exchange of NB takes place by influencing, directly or indirectly, the relative rates of renal tubular H- secretion and Cl- reabsorption at any given rate of tubular reabsorption of Na-. Some cybernetic considerations of the disturbance are presented.

Acid-Base Equilibrium↗
PubMed1990

Prefrontal cortex and the bridging of temporal gaps in the perception-action cycle.

Normal behavior is characterized by a constant circular flow of influences from sensory receptors to motor effectors, to the physical environment, back to sensory receptors, and so on. This cybernetic cycle of influences (the perception-action cycle) governs all sequences of behavior to make them adaptive and goal directed. In the primate (including the human primate), considerable evidence indicates that dorsolateral prefrontal cortex is essential for the bridging of temporal gaps in the perception-action cycle, in other words, for mediating cross-temporal contingencies of behavior. This chapter summarizes some neuropsychological and neurophysiological evidence in support of this conclusion. The evidence has been obtained from monkeys performing delay tasks, which epitomize the principle of cross-temporal contingency.

Animals↗
PubMed2000

Organizational closure and conceptual coherence

This paper reviews ideas developed by the late Gordon Pask as part of this conversation theory (CT). CT uses theories of the dynamics of complex, self-organizing systems, in conjunction with models of conceptual structures, in order to give an account of conceptual coherence (for example, of a theory or a belief system) as a form of organizational closure. In Pask's own terms, CT is concerned both with the kinematics of knowledge structures and the kinetics of knowing and coming to know. The main features of modelling conceptual structures and processes used by Pask are presented. We continue by presenting a summary two-cycle model of learning, aimed to capture some of Pask's key insights with respect to conceptual coherence and the organizational closure of conceptual systems. Parallels are drawn with other work in epistemology, classic cybernetic studies of self-organization, and the concept of autopoiesis. The two-cycle model is then applied recursively to generate learning cycles and conceptual structures at different levels of abstraction, as a contribution to the work of Pask on the topology of thought. Finally, the model is applied reflexively. That is, its own form is considered as a topic for conversation and conceptualization. Carrying out such a reflection provides a coherent way of characterizing epistemological limits, while retaining a clear sense of there being an (in principle) unlimited praxeology of awareness.

Journal Article↗
PubMed1999

Toward a theory of constraints.

Grounded in the cybernetic concept of negative explanation, the theory of constraints examines how human systems are kept from solving problems. To identify constraints, therapists must know where to look for them and what to look for. The theory proposes that constraints exist among the levels of a biopsychosocial system, which include biology, person, relationship, family, community, and society. The six metaframeworks of organization, sequences, mind, development, gender, and culture assist constraint identification. Combining the levels and metaframeworks creates a web of constraints, the complexity of which determines how difficult it will be to solve a given problem. The theory of constraint offers an integrative and pragmatic approach to therapy while simultaneously honoring the complexity of human systems.

Adult↗
PubMed1971

Perception of changes in certain exteroceptive stimuli.

Although cybernetic models of one sort or another have become quite common in behavioral research, and although these models theoretically require a capacity for system detection of changes in error, no general psychophysical description of the individual human being's ability to discriminate different rates of stimulation is available. An initial survey of this type has been attempted and is reported here. For reasons which appear to be related to the biological mechanisms underlying sensory information processing, it is concluded, first, that ancillary cues of rate-related final magnitude are more valuable than cues of stimulus duration; second, that direct attention to on-going change is less precise than attention to final values only; and third, that differences in isochronal stimulus rates occurring in place or extent are more readily perceived than differences in isochronal rate of change in energy content, at least for the stimuli and ranges examined.

Auditory Perception↗
PubMed2006

Hypoplasia and neuronal immaturity of the hypoglossal nucleus in sudden infant death.

OBJECTIVE: To report the case of five month old female baby with a history of episodes of gastro-oesophageal reflux and pneumonia. Her sudden death offered a unique insight into the possible role of delayed neuronal maturation and hypoplasia of the hypoglossal nucleus in representing a likely morphological substrate of sudden death. METHODS: Morphometric analysis was carried out with an Image-Pro Plus Image analyser (Media Cybernetics) on both sides of the brain stem. RESULTS: Hypoplasia and neuronal immaturity of the hypoglossal nucleus were demonstrated, accompanied by hypoplasia of the arcuate nucleus. CONCLUSIONS: Much attention should be paid to the possible role of the hypoglossal nucleus in determining a lethal outcome in infancy through impairment of deglutition and subsequent recurrent episodes of pneumonia, and as a necropsy finding.

Adult↗
PubMed2005

Human development: biological and genetic processes.

Adaptation is a central organizing principle throughout biology, whether we are studying species, populations, or individuals. Adaptation in biological systems occurs in response to molar and molecular environments. Thus, we would predict that genetic systems and nervous systems would be dynamic (cybernetic) in contrast to previous conceptualizations with genes and brains fixed in form and function. Questions of nature versus nurture are meaningless, and we must turn to epigenetics--the way in which biology and experience work together to enhance adaptation throughout thick and thin. Defining endophenotypes--road markers that bring us closer to the biological origins of the developmental journey--facilitates our understanding of adaptive or maladaptive processes. For human behavioral disorders such as schizophrenia and autism, the inherent plasticity of the nervous system requires a systems approach to incorporate all of the myriad epigenetic factors that can influence such outcomes.

Adaptation, Psychological↗
PubMed1982

The tides of human consciousness: descriptions and questions.

A Rosetta Stone has appeared in our midst in the form of R. A. Wever's monograph The Circadian System of Man (New York: Springer-Verlag, 1979), describing the results of 20 years' experiments with J. Aschoff. In the January 1982 issue of this journal, Kronauer, Czeisler, Pilato, Moore-Ede, and Weitzman offer their decipherment: a mathematical description of man's circadian temperature rhythm and sleep timing based on their own experimental observations in the Bronx, confirming and substantially extending Wever's in Bavaria. This paper might have been as happily received by the Journal of Mathematical Biology or Biological Cybernetics. Accordingly I here attempt to disentangle numerical description from physiological hypothesis, emphasizing items that seem, at least in principle, susceptible to experimental test.

Body Temperature Regulation↗
PubMed1988

Proposal for APS-IUPS convention for diagraming physiological mechanisms.

As physiological research reveals the existence of systems of increasing complexity and the existence of important interactions between them, the diagrammatic depiction of those systems and their interactions becomes an essential step in clarifying our own concepts in scientist-to-scientist communication and in teaching. Although control engineers, electronic engineers, and computer programmers long ago established their own diagrammatic conventions, physiologists are only now beginning to feel the need for a uniform convention suited to their own special needs in place of the numerous (and mostly ad hoc) diagram types that have recently proliferated in the literature. The convention proposed here is based on a formal theory of mechanism developed by W. Ross Ashby (An Introduction to Cybernetics, 1956). Its purely mechanistic structure transcends traditional interdisciplinary barriers to communication. Wide acceptance of the convention proposed here would therefore enhance the ability of physiology to encompass mechanisms from molecular and cell biology and integrate them with general and systems physiology in a metadisciplinary effort to comprehend "the wisdom of the body." Among its many advantages is its simplicity; diagrams may be drawn at various levels of detail and complexity by use of a few basic rules, and they can be readily understood without knowledge of the theory.

Algorithms↗
PubMed2005

Postural control in man: the phylogenetic perspective.

Erect posture in man is a recent affordance from an evolutionary perspective. About eight million years ago, the stock from which modern humans derived split off from the ape family, and from around sixty-thousand years ago, modern man developed. Upright gait and manipulations while standing pose intricate cybernetic problems for postural control. The trunk, having an older evolutionary history than the extremities, is innervated by medially descending motor systems and extremity muscles by the more recent, laterally descending systems. Movements obviously require concerted actions from both systems. Research in rats has demonstrated the interdependencies between postural control and the development of fluent walking. Only 15 days after birth, adult-like fluent locomotion emerges and is critically dependent upon postural development. Vesttibular deprivation induces a retardation in postural development and, consequently, a retarded development of adult-like locomotion. The cerebellum obviously has an important role in mutual adjustments in postural control and extremity movements, or, in coupling the phylogenetic older and newer structures. In the human, the cerebellum develops partly after birth and therefore is vulnerable to adverse perinatal influences. Such vulnerability seems to justify focusing our scientific research efforts onto the development of this structure.

Animals↗
PubMed1993

Local gain control and focal accommodation in the Self Similar Stack vision model.

The aim of this paper is to report an extension to the computationally efficient Self Similar Stack model (Burton et al. Biol., Cybernet. 53, 397-403, 1986) to include the effects of local gain control in the retina. The method employed to do this has been to fit a family of difference-of-Gaussian functions to the human contrast sensitivity function curves of van Nes and Bouman (J. Opt. Soc. Am. 57, 401-406, 1967). The centre frequencies of the DoGs within each family are octave-related, in a simplified manifestation of the DoG channels found by Wilson et al. (Vision Res. 23, 873-882, 1983). The sensitivity of each level, or channel, that formed the original Stack model is modulated individually according to the fitted values, as the local illumination varies within an image. The model was tested against psychometric data obtained by Haig and Burton (Appl. Optics 26, 492-500, 1987) during experiments on visual discrimination. The consistency of the results indicates the validity of the approximations and the robustness of the model, either for machine vision purposes or for predicting human visual performance. A simple algorithm, developed for use with a machine vision application of this model, provides a means by which a TV camera may be focused automatically. The success of this algorithm, using the newly computed channel sensitivities, suggests that human focal accommodation may be regulated by a similar form of mechanism.

Accommodation, Ocular↗