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P E Rapp

Publications and source records attributed to P E Rapp.

At least 19 recordsLinked to original sources
PubMed1996

Re-examination of the evidence for low-dimensional, nonlinear structure in the human electroencephalogram.

We have re-examined single channel EEG data obtained from normal human subjects. In the original analysis, calculation of the correlation dimension with the Grassberger-Procaccia algorithm produced results consistent with and interpretation of low-dimensional behavior. The re-examination suggests that the previous indication of low-dimensional structure was an artifact of autocorrelation in the oversampled signal. Calculations with a variant of the Grassberger-Procaccia algorithm modified to be less sensitive to autocorrelations, and comparison with linear gaussian surrogate data, indicate that these data may be more appropriately modeled by linearly filtered noise. Discriminant analysis further indicates that the correlation dimension is a poor discriminator for distinguishing between EEGs recorded at rest and during periods of cognitive activity. It remains possible that the application of other nonlinear measures or the examination of multichannel EEG data may resolve structures not found in these calculations.

Adult↗
PubMed1996

Complexity measures in molecular psychiatry.

The most frequently used measures in behavioral research are distribution-determined measures that provide a quantitative determination of the relative frequency of a specified behavior. These measures are, however, insensitive to the sequence of behaviors. Complexity measures address this deficiency. Several sequence-sensitive measures including the topological entropy, metric entropy, algorithmic complexity and stochastic model complexity will be described. Several applications to psychiatric research will also be discussed. These applications include the characterization of changes in animal behavior in response to CNS-active drugs and the analysis of single-unit interspike interval spike trains. Clinical applications include the analysis of electromyographic and electroencephalographic signals, the examination of choice task behavior in clinical populations, and protocol analysis.

Algorithms↗
PubMed1994

The algorithmic complexity of neural spike trains increases during focal seizures.

The interspike interval spike trains of spontaneously active cortical neurons can display nonrandom internal structure. The degree of nonrandom structure can be quantified and was found to decrease during focal epileptic seizures. Greater statistical discrimination between the two physiological conditions (normal vs seizure) was obtained with measurements of context-free grammar complexity than by measures of the distribution of the interspike intervals such as the mean interval, its standard deviation, skewness, or kurtosis. An examination of fixed epoch data sets showed that two factors contribute to the complexity: the firing rate and the internal structure of the spike train. However, calculations with randomly shuffled surrogates of the original data sets showed that the complexity is not completely determined by the firing rate. The sequence-sensitive structure of the spike train is a significant contributor. By combining complexity measurements with statistically related surrogate data sets, it is possible to classify neurons according to the dynamical structure of their spike trains. This classification could not have been made on the basis of conventional distribution-determined measures. Computations with more sophisticated kinds of surrogate data show that the structure observed using complexity measures cannot be attributed to linearly correlated noise or to linearly correlated noise transformed by a static monotonic nonlinearity. The patterns in spike trains appear to reflect genuine nonlinear structure. The limitations of these results are also discussed. The results presented in this article do not, of themselves, establish the presence of a fine-structure encoding of neural information.

Algorithms↗
PubMed1993

Optimal digital filters for long-latency components of the event-related brain potential.

A fundamentally important problem for cognitive psychophysiologists is selection of the appropriate off-line digital filter to extract signal from noise in the event-related brain potential (ERP) recorded at the scalp. Investigators in the field typically use a type of finite impulse response (FIR) filter known as moving average or boxcar filter to achieve this end. However, this type of filter can produce significant amplitude diminution and distortion of the shape of the ERP waveform. Thus, there is a need to identify more appropriate filters. In this paper, we compare the performance of another type of FIR filter that, unlike the boxcar filter, is designed with an optimizing algorithm that reduces signal distortion and maximizes signal extraction (referred to here as an optimal FIR filter). We applied several different filters of both types to ERP data containing the P300 component. This comparison revealed that boxcar filters reduced the contribution of high-frequency noise to the ERP but in so doing produced a substantial attenuation of P300 amplitude and, in some cases, substantial distortions of the shape of the waveform, resulting in significant errors in latency estimation. In contrast, the optimal FIR filters preserved P300 amplitude, morphology, and latency and also eliminated high-frequency noise more effectively than did the boxcar filters. The implications of these results for data acquisition and analysis are discussed.

Adult↗
PubMed1992

Three quantitative studies of gender and identity in psychotherapy consultations.

This paper details the application of three distinctive approaches to the analysis of line-by-line scores for themes of gender and identity in recorded psychotherapy consultations conducted by three male analysts with a female patient. The first method involved commonly used statistical comparisons of the frequency with which gender subthemes and allusions to identity appeared in each consultation session. The results of this study indicate three significantly different patterns of gender material in the communications from the patient with each of the analysts who interviewed her--and from each analyst and patient/analyst system as well. Therapist dominance in this area appeared to be quite strong. The second study involved measures of overall informational complexity for various aspects of the gender/identity sequence of communications. Here too, individual differences emerged. They not only add to the evidence for therapist dominance in these protocols, but also provide indications that sessions differ in respect to the extent to which the information they contain is ordered and repetitive or redundant, as compared to disordered, complex, and varied. The third study availed itself of stochastic methods in which the Box-Jenkins models were used to define mathematically and post hoc, the deeper structure of aspects of the vicissitudes of gender/identity expressions in the course of these consultations. The main finding was that change in speaker role in respect to these themes accelerated in response to random interventional shocks to the system that occurred at the time of measurement and inversely with shocks to the system sustained the previous second. This look into the deeper structure of these sequences revealed considerable sensitivity to recent shocks to the patient/therapist system, much underlying instability, and strong tendencies toward establishing stability or equilibrium when the system destabilized. Of note is the finding that all three consultations, by and large, followed the same configuration--itself a rarely seen model. The implications and promise of these methods are discussed.

Adult↗
PubMed1991

Toward a quantitative characterization of patient-therapist communication.

The efficacy of psychotherapy, in its many and varied forms, is one of the most intensely contested issues in clinical practice. Though many theories have been advanced, quantitative evidence in their defense is limited. This contribution is directed to relatively unambitious objectives. Rather than establish yet another qualitative theory of psychotherapeutic practice, we wish to contribute to the construction of research methodologies that can quantitatively characterize the dynamic patterns of patient-therapist communication. It is hoped that a theoretical understanding of psychotherapy might eventually emerge naturally from a growing body of quantitative data.

Communication↗
PubMed1989

Saltatory transitions are a naturally occurring property of evolving systems.

On the basis of paleological evidence, it has been suggested that biological evolution need not necessarily be characterized by gradual change. Rather, evolutionary history may display saltatory periods of rapid speciation alternating with periods of relative quiescence, the whole dynamic being called punctuated equilibria. The empirical evidence that has been presented in support of this hypothesis has been the object of a vigorous dispute. Mathematical investigations of complex models of biological evolution that contain random elements have demonstrated that these systems can display saltatory behavior. In this paper we address a more abstract question: can saltations occur in the evolution of very simple, deterministic mathematical systems that function in a constant environment? The answer appears to be yes. Saltations appear as a natural dynamical behavior in the evolution of simplistic information processing networks. We stress that these networks do not constitute a model of biological evolution. However, the appearance of saltations in such simple systems suggests that their appearance in a process as complex as biological evolution is not surprising.

Animals↗
PubMed1987

Why are so many biological systems periodic?

The ubiquity of oscillations in biological systems is well established. Oscillations are observed in all types of organisms from the simplest to the most complex. Periods can range from fractions of a second to months or years. From time to time, it has been suggested that many biological oscillations are the result of the breakdown of effective self-regulation. The opposite view is defended here. It is argued that most periodic behavior is not pathological but rather constitutes the normal operation for these systems. They are present because they confer positive functional advantages for the organism. The advantages fall into five general categories: temporal organization, spatial organization, prediction of repetitive events, efficiency and precision of control.

Adaptation, Biological↗
PubMed1986

The bidirectional flux of cholesterol between cells and lipoproteins. Effects of phospholipid depletion of high density lipoprotein.

The bidirectional surface transfer of free cholesterol (FC) between Fu5AH rat hepatoma cells and human high density lipoprotein (HDL) was studied. Cells and HDL were prelabeled with [4-14C]FC and [7-3H]FC, respectively. Influx and efflux of FC were measured simultaneously from the appearance of 3H counts in cells and 14C counts in medium. Results were analyzed by a computerized procedure which fitted sets of kinetic data to a model assuming that cell and HDL FC populations each formed a single homogeneous pool and that together the pools formed a closed system. This analysis yielded values for the first-order rate constants of FC influx and efflux (ki and ke), from which influx and efflux of FC mass (Fi and Fe) could be calculated. With normal HDL, the uptake and release of FC tracers conformed well to the above-described model; Fi and Fe were approximately equal, suggesting an exchange of FC between cells and HDL. HDL was depleted of phospholipid (PL) by treatment with either phospholipase A2 or heparin-releasable rat hepatic lipase, followed by incubation with bovine serum albumin. PL depletion of HDL had little or no effect on ki, but reduced ke, indicating that PL-deficient HDL is a relatively poor acceptor of cell cholesterol. The reduction in ke resulted in initial Fi greater than Fe and, thus, in net uptake of FC by the cells. This result explained previous results demonstrating net uptake of FC from PL-depleted HDL. In the presence of an inhibitor of acyl coenzyme A:cholesterol acyltransferase, the steady state distribution of FC mass between cells and HDL was accurately predicted by the ratio of rate constants for FC flux. This result provided additional validation for describing FC flux in terms of first-order rate constants and homogeneous cell and HDL FC pools.

Animals↗
PubMed1985

Communication and control in reproduction: the ubiquity of periodic phenomena.

Two statements will be presented and defended in this paper. First, it is claimed that oscillations are common in all biological systems. From the subcellular to the organismic levels of organization, oscillations are the normal operational mode for many biochemical and physiological control networks. Second, it will be demonstrated that periodic control offers several functional advantages over steady-state control.

Animals↗
PubMed1979

A comparative survey of the function, mechanism and control of cellular oscillators.

This review attempts to survey in a uniform manner the available evidence concerning the generation and behaviour of several well-investigated cellular oscillators. Members of two broad classifications are contrasted: (i) cytoplasmic oscillations, where the periodic phenomena is generated by an instability pathway and (ii) membrane oscillators in which a membrane potential rhythm is generated at the membrane. Interactions between the cytoplasmic and membrane compartments are considered and the effects of these interactions on oscillatory behaviour is discussed. Because of their biological importance and the greater body of experimental results, particular attention is directed to a study of membrane potential oscillations. These systems can be approximately classified in two groups: (i) systems in which a periodic potential results from oscillatory changes in permeability and (ii) systems in which potential oscillations result from the periodic activity of an electrogenic pump. The examples considered include the glycolytic oscillator, oscillations in vein contraction in the slime mould Physarum polycephalum, rhythmic aggregation in Dictyostelium discoideum, neural oscillators, the periodic potential in Purkinje fibres and the sino-atrial node and rhythmic behaviour in smooth muscle. Questions considered include the generation of periodic activity, the modulation of the oscillation by drugs and other metabolic and membrane effectors and the question of the functional role of these oscillations.

Adrenal Cortex↗
PubMed1978

Periodic metabolic systems: oscillations in multiple-loop negative feedback biochemical control networks.

For a general multiple loop feedback inhibition system in which the end product can inhibit any or all of the intermediate reactions it is shown that biologically significant behaviour is always confined to a bounded region of reaction space containing a unique equilibrium. By explicit construction of a Liapunov function for the general n dimensional differential equation it is shown that some values of reaction parameters cause the concentration vector to approach the equilibrium asymptotically for all physically realizable initial conditions. As the parameter values change, periodic solutions can appear within the bounded region. Some information about these periodic solutions can be obtained from the Hopf bifurcation theorem. Alternatively, if specific parameter values are known a numerical method can be used to find periodic solutions and determine their stability by locating a zero of the displacement map. The single loop Goodwin oscillator is analysed in detail. The methods are then used to treat an oscillator with two feedback loops and it is found that oscillations are possible even if both Hill coefficients are equal to one.

Feedback↗
PubMedDate not supplied

Dynamics of brain electrical activity.

In addition to providing important theoretical insights into chaotic deterministic systems, dynamical systems theory has provided techniques for analyzing experimental data. These methods have been applied to a variety of physical and chemical systems. More recently, biological applications have become important. In this paper, we report applications of one of these techniques, estimation of a signal's correlation dimension, to the characterization of human electroencephalographic (EEG) signals and event-related brain potentials (ERPs). These calculations demonstrate that the magnitude of the technical difficulties encountered when attempting to estimate dimensions from noisy biological signals are substantial. However, these results also suggest that this procedure can provide a partial characterization of changes in cerebral electrical activity associated with changes in cognitive behavior that complements classical analytic procedures.

Brain↗