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PubMedDate not supplied

Participation of nonlinear dynamic processes in the formation of the high-frequency EEG of the rabbit.

The informativeness of the high-frequency EEG for the assessment of the functional state of the brain has been proven by means of a new method of analysis of the EEG which is suitable, by contrast with the traditional spectral correlation analysis, for the description of nonlinear processes. Evidence has been obtained in favor of the hypothesis that a deterministic chaotic component, the parameters of which depend on the region of recording of the EEG and which changes conjointly with change in the functional state of the brain, is present in the EEG of the neocortex and hippocampus of the rabbit.

Animals↗
PubMed1978

[Perception of your body. A psychoanalytical approach].

This paper discusses body-perception from a psychoanalytic point of view. Ia attempts a "totalizing" view of human behavior which integrates the whole of perception-thought-action-perception as a single process of organism-environment interaction. The underlying episthemological framework implies the rejection of lineal causal deterministic explanations in favor of a dynamic conception, in terms of feed-back mechanisms. Thus it discards the various false oppositions between "body-perception" and "object-perception"; and between cognition, affectivity and connation. The former is resolved through the recognition of the fact that perception is always a comparative process, which results from the organism-environment interaction. The comparative element for body-perception is the dynamic unconsious body scheme. The latter opposition is resolved through the application of the basic psychoanalytic model, which integrates the primary models for cognition, affectivity and connation.

Body Image↗
PubMed1990

Modelling of microbial processes that govern degradation of organic substrates in soil, with special reference to pesticides.

We tried to develop deterministic models for kinetics of 2,4-D breakdown in the soil based on the following considerations: (i) at low concentrations degradation results from maintenance consumption by a large fraction of the soil microbial population; (ii) at high concentration in addition to the maintenance consumption there is a growth-associated carbon incorporation by a small specific microbial population. Values for the biokinetic parameters are consistent with those commonly found in the literature. Comparison between observed and simulated curves suggests that a non-negligible part of the pesticidal carbon exists as microbial by-products.

2,4-Dichlorophenoxyacetic Acid↗
PubMed1988

Is the normal heart a periodic oscillator?

With the help of several independent methods of nonlinear dynamics, the electrocardiograms (ECG) of four normal human hearts are studied qualitatively and quantitatively. A total of 36 leads were tested. The power spectrum, the autocorrelation function, the phase portrait, the Poincaré section, the correlation dimension, the Lyapunov exponent and the Kolmogorov entropy all point to the fact that the normal heart is not a perfect oscillator. The cardiac activity stems from deterministic dynamics of chaotic nature characterized by correlation dimensions D2 ranging from 3.6 to 5.2. Two different phase spaces are constructed for the evaluation of D2: the introduction of time lags and the direct use of space vectors give similar results. It is shown that the variabilities in interbeat intervals are not random but exhibit short range correlations governed by deterministic laws. These correlations may be related to the accelerating and decelerating physiological processes. This new approach to the cardiac activity may be used in clinical diagnosis. Also they are valuable tools for the evaluation of mathematical models which describe cardiac activity in terms of evolution equations.

Electrocardiography↗
PubMed1976

Biochemical markers of ischemic injury.

Enzymatic estimation of infarct size entails assumptions requiring analysis and modification during evolution of the method. Myocardial creatine phosphokinase (CPK) depletion reflects infarct size under many experimental conditions, and release of CPK into the circulation has been correlated with histologically demonstrable necrosis. Use of a one compartment model relating serum CPK changes to myocardial CPK depletion is a simplification requiring estimates of CPK disappearance rate (kd) as one parameter. Conformity of kd to first order kinetics and its lack of variance despite marked hemodynamic perturbations, myocardial infarction per se, or successive daily determinations have been documented. In patients with myocardial infarction, enzymatic estimates of infarct size correlate with morbidity and mortality, functional cardiac impairment, severity of clinical manifestations, frequency of ventricular dysrhythmia, and morphologically estimated infarct size. Improved estimates result from MB CPK analyses which avoid difficulties due to noncardiac CPK in the circulation and from individualization of values of kd. The discriminant power of enzymatic estimates as an index of prognosis has been demonstrated by discriminant function analysis. Prediction of infarct size enzymatically requires additional assumptions and conventionally employs an empirical algorithm rather than a physiological, deterministic model. Although predictions can probably be improved by incorporation of parameters reflecting processes governing CPK release and disappearance, the need for a prolonged interval during which observations are required prior to prediction limit the applicability of this approach to evaluation of therapeutic interventions whose effects are likely to be maximum when early implementation is possible.

Animals↗
PubMed1982

Reduction of EEG activity caused by a light flash.

Intertrial EP variance measured in response to a brief binocularly presented flash of light decreases with a time-course that overlaps the average EP. This decrease in variance is not exclusive to the alpha frequency band (8-12 c/sec) but it is selective for it. Subjects with large initial variance tend to show a large decrease in variance. There is no relationship between the magnitude of the decrease in variance and the consistency of the EP. The phenomenon reflected by the decrease in variance is probably identical with 'event-related desynchronization.' The results support the hypothesis that an EP may consist of two processes that overlap in time: a reduction in background EEG activity and an almost deterministic transient potential change.

Brain↗
PubMed1991

A mathematical model of rinderpest infection in cattle populations.

A mathematical model for the epidemiology of rinderpest was developed, starting from a simplified descriptive analysis of the disease. A formula for the calculation of the probability of infection of a susceptible animal was first established. A deterministic failure threshold of the infection was then deduced. Deterministic and stochastic approaches were adopted using iterative methods on a computer. These allowed a description of the spread and the variability of an infection process in a population to be made. An illustration of the use of this model showed that, in some cases, variability effects due to stochastic factors were very important. In these particular conditions, the use of the deterministic model alone was not adequate for a good description of the infection. Consequently, improvements of the model were proposed in order to make it more realistic and to allow its use for the evaluation of the efficiency of field operations.

Animals↗
PubMed1990

The regulation of gastrointestinal helminth populations.

One quarter of the world's human population suffers infection with helminth parasites. The population dynamics of the ten or so species, which cause disease of clinical significance have been well characterized by epidemiological field survey. The parasites are in general highly aggregated between hosts, and their populations seem to be temporally stable and to recover rapidly from perturbation, including interventions designed to alleviate disease. This paper reviews current understanding of the population regulation of helminth species of medical significance. Both empirical (field and laboratory) and theoretical results are included, and we attempt to interpret the findings in the broader context of the population ecology of free-living species. We begin by considering the evidence for regulation from field data concerning the temporal stability of helminth populations within communities and from the results of perturbation experiments. The detection of regulatory processes is then discussed (with regard to statistical and logistical considerations), and the evidence from both the field and laboratory studies reviewed. Deterministic models are described to investigate the possible consequences of regulation imposed at different points in the parasite life-cycle. The causes and consequences of parasite aggregation are considered, and a stochastic model used to investigate the impact of different combination of regulatory processes and heterogeneity generating mechanisms.

Animals↗
PubMed1989

Adaptive numerical smoothing: an efficient method of conditioning physiological signals.

The main aim of the paper is to present a method of reducing the number of necessary operations in the process of numerically smoothing digitised signals, together with increasing the quality of smoothing, using suggestions which are new in the technique of numerical smoothing. The first suggestion consists of an analytical description of the smoothing process and the representation of the input mixture and undergoing smoothing signals by a series of sinc functions. The second proposal consists of using adaptive smoothing, i.e. smoothing with varying step and with some special means for increasing the quality of smoothing. These procedures must be calculated together with the processing and this procedure causes a small delay in the output signal. The approach presented is a deterministic one, i.e. the information about all instantaneous values of the input mixture is used instead of an a priori average information about disturbances. Attention is directed towards disturbances which are associated with physiological signals such as pressure, flow and electrocardiogram waveforms. The paper contains the basic theory and some experimental results which demonstrate the potential of adaptive smoothing.

Electrocardiography↗
PubMed2025

Repeatable Genomic Outcomes Along the Speciation Continuum: Insights From Pine Hybrid Zones (Genus Pinus).

Hybridization is a widespread evolutionary process and a key source of evolutionary novelty. Despite intensive study, the extent to which hybridization is deterministic and repeatable, particularly in recurrent contact events involving the same species under varying ecological conditions, remains unclear. Here, we investigated three replicated contact zones between Scots pine (Pinus sylvestris) and dwarf mountain pine (Pinus mugo) in Central Europe: two occurring in peatland habitats and one in a contrasting sandstone outcrop. Using genome-wide SNP genotyping of over 1300 individuals, we analysed genomic structure, diversity, and ancestry patterns across these zones. All sites revealed pervasive hybridization, dominated by later-generation hybrids and a notable scarcity of pure P. mugo. Across environments, hybrid populations exhibited strikingly consistent genomic compositions, with asymmetric introgression strongly biased toward P. mugo ancestry, suggesting that hybrid genome structure may follow predictable patterns under similar ecological conditions and could be shaped by cytonuclear incompatibilities. Nonetheless, we also detected site-specific differences in hybrid diversity and phenotype, highlighting the influence of local environmental selection on shared hybrid genomic backgrounds. We provide genomic evidence that Pinus uliginosa, a morphologically distinct peat bog pine traditionally regarded as a relict and endangered species is instead a partially stabilised hybrid lineage. Its genome reflects incomplete hybridization and ecological filtering, yet it lacks sufficient genetic divergence to be recognised as a distinct species. Together, these results provide evidence for the repeatability of hybridization processes, which result in the formation of phenotypes reflecting a species continuum subjected to strong environmental pressures. The findings support the simplification of taxonomic nomenclature within the Pinus mugo complex, informing adaptive conservation strategies and the genetic management of hybrid lineages.

Hybridization, Genetic↗
PubMed1991

[Medical diagnosis].

The diagnostic process holds a firm position in medical practice, but is often claimed to be part of the "art of medicine", partially beyond reach of rational and logical analysis. Research in clinical cognition, decision analysis and artificial intelligence have, however, elucidated essential parts of medical diagnosis. A characteristic feature of diagnosis is the manner in which uncertainties are handled. Early generation of hypotheses about the nature of the condition present seems to be useful method. Similarly, probabilistic, causal and deterministic reasoning can be illustrated by diagnostic models which have found favor during recent years. A certain type of cognitive process (heuristic) is employed when assessing information of probabilistic nature. The diagnostic models are partial and concern the parts of the process, which may be represented verbally and consciously. This raises the question of how the clinician actually draws upon experience (background knowledge), which preconditions shape the generation of applicable diagnostic hypotheses and how the diagnostic capability of the individual physician can be facilitated.

Clinical Competence↗
PubMed1982

Motor command in the ventrolateral thalamic nucleus: neuronal variability can be overcome by ensemble average.

The variability and stationarity of single unit activity and reaction times in a simple reaction time task were investigated by means of unit recordings from the ventrolateral thalamic nucleus in the cat. The study was carried out on eight neurons recorded over many trials and displaying an increase in activity correlated with the performed reaction time. The stationarity of the correlation appeared to be better than that of the unit activity or reaction time taken alone. In this stationary process the neuronal variability is considerable, and the investigator has to use time averages over many trials to be able to extract information from the single unit data. Since the nervous system does not required repeated presentations of a stimulus to trigger a movement, it must be using parallel processing of information throught ensemble averages. A simulation of an ensemble average based upon the data from these eight neurons showed that such a process can be efficient. An evaluation of the number of neurons required to obtain a quasi deterministic neuronal command of the reaction time value, gave the speculative figure of 70. This figure could represent the dimension of the set of neurons with the same characteristics involved in the motor command.

Animals↗
PubMed1985

Predictions of knee and ankle moments of force in walking from EMG and kinematic data.

A deterministic model was developed and validated to calculate instantaneous ankle and knee moments during walking using processed EMG from representative muscles, instantaneous joint angle as a correlate of muscle length and angular velocity as a correlate of muscle velocity, and having available total instantaneous joint moments for derivation of certain model parameters. A linear regression of the moment on specifically processed EMG, recorded while each subject performed cycled isometric calibration contractions, yielded the constants for a basic moment-EMG relationship. Using the resultant moment for optimization, the predicted moment was proportionally augmented for longer muscle lengths and reduced for shorter lengths. Similarly, the predicted moment was reduced for shortening velocities and increased if the muscle was lengthening. The plots of moments predicted using the full model and those calculated from link segment mechanics followed each other quite closely. The range of root mean square errors were: 3.2-9.5 Nm for the ankle and 4.7-13.0 Nm for the knee.

Ankle Joint↗
PubMed1992

Adaptive filter for event-related bioelectric signals using an impulse correlated reference input: comparison with signal averaging techniques.

Many bioelectric signals result from the electrical response of physiological systems to an impulse that can be internal (ECG signals) or external (evoked potentials). In this paper an adaptive impulse correlated filter (AICF) for event-related signals that are time-locked to a stimulus is presented. This filter estimates the deterministic component of the signal and removes the noise uncorrelated with the stimulus, even if this noise is colored, as in the case of evoked potentials. The filter needs two inputs: the signal (primary input) and an impulse correlated with the deterministic component (reference input). We use the LMS algorithm to adjust the weights in the adaptive process. First, we show that the AICF is equivalent to exponentially weighted averaging (EWA) when using the LMS algorithm. A quantitative analysis of the signal-to-noise ratio improvement, convergence, and misadjustment error is presented. A comparison of the AICF with ensemble averaging (EA) and moving window averaging (MWA) techniques is also presented. The adaptive filter is applied to real high-resolution ECG signals and time-varying somatosensory evoked potentials.

Algorithms↗
PubMed1991

Risk prevention and policy-making in automatic systems.

Accidents with automatic production systems are reported to be on the order of one in a hundred or thousand robot-years, while fatal accidents are found to occur one or two orders of magnitude less frequently. Traditions in occupational safety tend to seek for safety targets in terms of zero severe accidents for automatic systems. Decision-making requires a risk assessment balancing potential risk reduction measures and costs within the cultural environment of a production company. This paper presents a simplified procedure which acts as a decision tool. The procedure is based on a risk concept approaching prevention both in a deterministic and in a probabilistic manner. Eight accident scenarios are shown to represent the potential accident processes involving robot interactions with people. Seven prevention policies are shown to cover the accident scenarios in principle. An additional probabilistic approach may indicate which extra safety measures can be taken against what risk reduction and additional costs. The risk evaluation process aims at achieving a quantitative acceptable risk level. For that purpose, three risk evaluation methods are discussed with respect to reaching broad consensus on the safety targets.

Accidents, Occupational↗
PubMed1989

A class of linear spectral models and analyses for the study of longitudinal data.

Longitudinal data can always be represented by a time series with a deterministic trend and randomly correlated residuals, the latter of which do not usually form a stationary process. The class of linear spectral models is a basis for the exploratory analysis of these data. The theory and techniques of factor analysis provide a means by which one component of the residual series can be separated from an error series, and then partitioned into a sum of randomly scaled metameters that characterize the sample paths of the residuals. These metameters, together with linear modelling techniques, are then used to partition the nonrandom trend into a determined component, which is associated with the sample paths of the residuals, and an independent inherent component. Linear spectral models are assumption-free and represent both random and nonrandom trends with fewer terms than any other mixed-effects linear model. Data on body-weight growth of juvenile mice are used in this paper to illustrate the application of linear spectral models, through a relatively sophisticated exploratory analysis.

Animals↗
PubMed1991

Chaos or noise in EEG signals; dependence on state and brain site.

EEG signals have been considered to result either from random processes or to be generated by non-linear dynamic systems exhibiting chaotic behaviour. In the latter case, the system may behave as a deterministic chaotic attractor. The complexity of the attractor can be characterized by the correlation dimension that can be computed from one signal generated by the system. A new procedure was developed and applied in order to test whether the correlation dimension, calculated from an EEG epoch, may correspond to a chaotic attractor or to a random process. This procedure was applied to EEG signals recorded from different sites of the limbic cortex of the rat during different states: wakeful rest, locomotion and in the course of an epileptic seizure induced by kindling. The signals recorded during the first two states had high dimensions and could not be distinguished from random noise. However, during an epileptic seizure the correlation dimension became low (between 2 and 4) indicating that in this state the networks behave as chaotic systems. A low correlation dimension appeared at different times and brain sites during an epileptic seizure. These results show that the computation of the correlation dimension may be useful in order to obtain insight into the dynamics of the propagation of an epileptic seizure in the brain.

Animals↗
PubMed1988

Neural perspectives of cerebral correlates of giftedness.

Giftedness is defined as some special endowment or propensity for creativity, skill, and eminent achievement, found in relatively few individuals among the population. A high order of mental power (IQ), creativity, and motivation (task commitment) appear to be the most universally recognized attributes of the gifted. This report summarizes current knowledge of the cerebral correlates of intelligence and creativity, including physiological measures of EEG, cortical power spectrum, brain evoked potentials, and positron emission tomography. Controversy, debates, contentions, formal hypotheses, and research issues are considered. We are especially interested in the formulation of the deterministic function of EEG-brain dynamics. A CHAOS modeling on hierarchy of cognitive organization and cerebral processing in the gifted is suggested.

Adaptation, Psychological↗