Showing papers in "Integrative Physiological and Behavioral Science in 1994"

Mechanism of the human diving response

Abstract: The diving response in human beings is characterized by breath-holding, slowing of the heart rate (diving bradycardia), reduction of limb blood flow and a gradual rise in the mean arterial blood pressure. The bradycardia results from increased parasympathetic stimulus to the cardiac pacemaker. The reduction in limb blood flow is due to vasoconstriction resulting from increased activity of the sympathetic nerves supplying arteries in the arms and legs. Essentially the response is produced by the combination of water touching the face and either voluntary or involuntary (reflex) arrest of breathing. The nervous inputs and outputs for the response are coordinated in the brain stem by the respiratory, vasomotor and cardioinhibitory “centers.” The diving response in human beings can be modified by many factors but the most important are water temperature, oxygen tension in the arterial blood and emotional factors.

The point correlation dimension: Performance with nonstationary surrogate data and noise

Abstract: The dynamics of many biological systems have recently been attributed to low-dimensional chaos instead of high-dimensional noise, as previously though. Because biological data are invariably nonstationary, especially when recorded over a long interval, the conventional measures of low-dimensional chaos (e.g., the correlation dimension algorithms) cannot be applied. A new algorithm, the point correction dimension (PD2i) was developed to deal with this fundamental problem. In this article we describe the details of the algorithm and show that the local mean PD2i will accurately track dimension in nonstationary surrogate data.

A guide to dynamical analysis.

Abstract: The number and variety of methods used in dynamical analysis has increased dramatically during the last fifteen years, and the limitations of these methods, especially when applied to noisy biological data, are now becoming apparent. Their misapplication can easily produce fallacious results. The purpose of this introduction is to identify promising new methods and to describe safeguards that can be used to protect against false conclusions.

Non-equilibrium dynamics as an indispensable characteristic of a healthy biological system.

Abstract: Healthy systems in physiology and medicine are remarkable for their structural variability and dynamical complexity. The concept of fractal growth and form offers novel approaches to understanding morphogenesis and function from the level of the gene to the organism. For example, scale-invariance and long-range power-law correlations are features of non-coding DNA sequences as well as of healthy heartbeat dynamics. For cardiac regulation, perturbation of the control mechanisms by disease or aging may lead to a breakdown of these long-range correlations that normally extend over thousands of heartbeats. Quantification of such long-range scaling alterations are providing new approaches to problems ranging from molecular evolution to monitoring patients at high risk of sudden death. We briefly review recent work from our laboratory concerning the application of fractals to two apparently unrelated problems: DNA organization and beat-to-beat heart rate variability. We show how the measurement of long-range power-law correlations may provide new understanding of nucleotide organization as well as of the complex fluctuations of the heartbeat under normal and pathologic conditions.

Identification of a Cortical Site for Stress-Induced Cardiovascular Dysfunction

Abstract: The evidence indicating that the insular cortex is a likely candidate to mediate stress-induced cardiovascular responses is reviewed. Both neuroanatomical and electrophysiological investigations demonstrate that the insular cortex receives an organized representation of visceral information. In addition, the insular cortex also receives highly processed association cortex information. The insular cortex is also highly interconnected with many subcortical limbic and autonomic regions. This combination of sensory input and limbic/autonomic connectivity would be necessary to permit the insular cortex to be a critical site for the integration of emotional and autonomic responses. Stimulation of the insular cortex elicits specific cardiovascular and autonomic responses from discrete sites. Phasic stimulation entrained to the cardiac cycle is even capable of causing severe arrhythmias. The efferent pathways and some of the neurotransmitter mechanisms have determined. It appears that the lateral hypothalamic area is the primary site of synapse for autonomic responses originating in the insular cortex and this information is relayed by NMDA glutamatergic receptors and modulated by neuropeptides including neuropeptide Y, neurotensin, leu-enkephalin and dynorphin. Finally, a rat stroke model, which includes the insular cortex in the infarct region indicates that disruption of the insula can produce substantial cardiac and autonomic abnormalities, which might be similar to those produced by stress. Some of the chronic neurochemical changes, including increases in opioids, neuropeptide Y and neurotensin in the central nucleus of the amygdala, which might be mediating these cardiovascular disturbances, have been determined.

Characterization of State Transitions in Spatially Distributed, Chaotic, Nonlinear, Dynamical Systems in Cerebral Cortex

Abstract: The neurons of cerebral cortex are largely autonomous and generate activity that is manifested in trains of microscopic axonal action potentials. The neurons interact by sparse but numerous synaptic connections to generate macroscopic dendritic activity patterns that are observed in electroencephalographic (EEG) waves. The macroscopic patterns are constructed by the populations and they shape the output of cortical neurons in parallel arrays. Sensory cortexes receive sensory information in the form of microscopic action potentials, which induce state transitions in population dynamics. Each state transition transforms sensory information to perceptual meaning. The EEG reflects both kinds of activity. The sensory input is accessed by time ensemble averaging, whereas the perceptual output is found by spatial ensemble averaging. Spatial phase gradients in the EEG are useful for identifying EEG segments in a sequence of state transitions in response to sensory input. The rapidity and flexibility with which they take place give strong reason to postulate that the mechanism for the construction of these sequences of patterns is a dynamical system operating in a chaotic domain.

Neurocardiac toxicity of racemic D,L-lactate fluids.

Abstract: Racemicd,l-lactate has long been used in burn therapy as Ringer’s lactate and in peritoneal dialysis fluid for treatment of renal failure. The d-lactate component of this racemic mixture is known to cause two forms of neurological toxicity in patients: encephalopathy and, in a subset of the population, panic reaction. Here we demonstrate that coma, similar in degree to that produced by blood levels of 75 mM ethanol was induced in rats by the intraperitoneal infusion of sodiumd-lactate sufficient to raise serumd-lactate concentration to 25 mM, whereas infusion of equal quantities of sodiuml-lactate produced no observable neurological effect. We further demonstrate that the intravenous infusion of racemicd,l-lactic acid into 48-hour fasted rats produced serious disturbances of cardiac rate and rhythm leading to death. When serumd-lactate concentration had reached 1–2 mM there was bradycardia, at 2–3 mM prolongation of QT interval, at 6–7 mM AV block with ectopic escape rhythms, and at 11 mM death in ventricular standstill or fibrillation. In contrast, intravenous infusion ofl-lactic acid to blood levels of 25 mM failed to produce any change in cardiac rhythm. On the other hand, the isolated working heart, free of influence from the central nervous system, displayed no change of cardiac rhythm or physiological function when perfused with 25 mM sodiumd,l-lactate.

Testing the determinism of EEG and MEG

Abstract: NEURAL MASS ACTIVITY produces irregular time series such as the EEG and MEG. It is already apparent, through visual inspection, that these time series cannot simply result ...J from an uncoordinated arbitrary firing of neurons. Indeed, we expect that neurons must cooperate and partially synchronize their firing patterns in order to produce meaningful output. Although we may believe that we have visually identified patterns within these irregular time series, attempts to systematically track the code with linear and stochastic statistical techniques have left us in frustration. More recently it has been suggested that the ability to trace the dynamics of a system (e.g., to freeze them in a state space, a space that is spanned by the system's variables) might decode more of the brain's cryptic and enigmatic language (Etbert, et aI., 1994). If the dynamics of the underlying system can be reduced to a set of deterministic laws, then the phase space trajectory will converge toward a subset of the phase-space. This invariant subset is referred to as an attractor. Given a particular time series, the initial question one may ask is if one can identify an attractor. If the answer is yes, then it is possible to view the series as a manifestation of a deterministic dynamic system (albeit possibly a very complex one). How can we gain information about the deterministic processes governing a particular nonlinear system? As a first step, it is possible to estimate the determinism inherent in a given time series. Kaplan & Glass (1992) developed a direct test for determinism in a given time series. This article introduces this method for analyzing EEG and MEG and presents comparisons with other nonlinear measures such as the fractal dimension. The ~ estimations of the fractal dimension of the EEG has received considerable attention starting with the studies of Agnes Babloyantz (Babloyantz, 1985; Babloyantz & Destexhe, 1986; Babloyantz, et aI., 1985. See Elbert, et aI., 1994, for a recent review). In principle, such an estimation of the fractal dimension of the system generating a time series requires a "sufficient number" of data points. Estimations of d-dimensional systems reach up to more than 10d points. When dimensions are estimated from physiological time series containing less than 10,000-20,000 points, the resulting values cannot be accepted as absolute terms. Results can only be interpreted when comparisons between different time series are made, such as those between conditions or groups. Furthermore, data are nonstationary, and the measures presume that the data generator does not change. Therefore, relative dif-

Changes of chaoticness in spontaneous EEG/MEG.

Abstract: Depending on the task being investigated in EEG/MEG experiments, the corresponding signal is more or less ordered. The question still open is how can one detect the changes of this order while the tasks performed by the brain vary continuously. By applying a static measurement of the fractal dimension or Lyapunov exponent, different brain states could be characterized. However, transitions between different states may not be detected, especially if the moments of transitions are not strictly defined. Here we show how the dynamical measure based on the largest local Lyapunov exponent can be applied for the detection of the changes of the chaoticity of the brain processes measured in EEG and MEG experiments. In this article, we demonstrate an algorithm for computation of chaoticity that is especially useful for nonstationary signals. Moreover, we introduce the idea that chaoticity is able to detect, locally in time, critical jumps (phase-transition-like phenomena) in the human brain, as well as the information flow through the cortex.

Discriminating deterministic versus stochastic dynamics in neuronal activity.

Abstract: An approach to discriminating deterministic versus stochastic dynamics from neuronal data is presented. Direct tests for determinism are emphasized, as well as using time series with clear physical correlates measured from small ensembles of neurons. Surrogate data are used to provide null hypotheses that the dynamics in our data could be accounted for by linear stochastic systems. Algorithms are given in full, and the analysis of an experimental example is given.

Rapid associative learning: conditioned bradycardia and its central nervous system substrates.

Abstract: It has become clear from the study of different response systems during classical conditioning that some responses are acquired quite rapidly and others show a much slower rate of acquisition. The most often studied rapidly acquired responses have been classically conditioned autonomic changes (e.g., heart rate); the slowly acquired responses most often studied are skeletal responses, such as the eyeblink or leg flexion response. Although there are various other differences between rapidly acquired and slowly acquired responses, we have suggested that the most important difference is the possibility that they represent different stages of the learning process. In the present review I describe research in our laboratory that has focused on conditioned bradycardia as a model system of a rapidly acquired associative system and contrast it with the more slowly acquired Pavlovian conditioned eyeblink response. I also describe the generality of conditioned bradycardia and discuss the differential role of subdivisions of the prefrontal cortex as a substrate for mediating this response. Finally, I briefly discuss the other brain areas involved in conditioned bradycardia, and its functional significance as it relates to the learning process.

Localized measures for nonstationary time-series of physiological data

Abstract: We will discuss localized measures related to the concepts of dimension, Lyapunove exponents (entropy), and recurrence diagrams. We stress the relevance of localized events and coincidences in physiological time series that often are lost when statistical averaging methods are applied. We suggest event-based statistics as an alternative to spectral or averaged-based statistics. The use of wavelets bases for characterizing localized structures is discussed as a potential alternative to Fourier-based analysis. Finally we mention how local domains in state space could be applied as triggers for external stimuli and thereby improve the statistics of ERP recordings.

Chaos in physiology

Abstract: A bird’s eye view of the role of nontrivial dynamical phenomena in physiological systems is presented. Many levels in the physiological hierarchy are affected. It appears that physiology has a particularly high affinity to chaos. The old central place of physiology in the circle of sciences can perhaps be regained if the two disciplines join resources. Even physics may turn out to be dependent on the chaotic micro dynamics of the brain.

Effects of stress on defensive aggression and dominance in a water competition test

Abstract: Water-deprived rats in a pair competing for a single source of water quickly establish a firm relationship during which one rat drinks consistently more (dominant) than the other (submissive) animal. This relationship is formed during the first competition and is very stable during subsequent tests. Exposure of dominant rats to a severe (18 hrs immobilization), but not a mild (2 hrs immobilization), stressor reduced markedly aggressive behavior and inverted transiently the dominant submissive relationship of the pairs. Exposure of submissive rats to the severe stressor resulted in only minor reductions of aggressive behavior in these animals. Prestress anxiety predicted stress effects in the dominant animals in that high-anxious animals lost more dominant behavior and weight during stress as compared with low-anxious rats. Thus, severe stress can transiently reduce dominant but not submissive behavior during water competition and high-anxious rats are more prone to lose their aggressive behavior.

Two tools to test time series data for evidence of chaos and/or nonlinearity.

Abstract: Two computer programs are described for evaluating the evidence for chaos and nonlinearity in time series data. “bx” is an efficient algorithm for computing the correlation integral (from which correlation dimension can be estimated); and “surrogat” is a Fourier-transform-based algorithm for generating surrogate data consistent with a null hypothesis that the data arise as a result of a linear stochastic process.

The revised monoamine hypothesis: mechanism of antidepressant treatment in the context of behavior.

Abstract: The temporal restoration of brain monoamines in the synaptic cleft due to MAO inhibition or by blocking catecholamine reuptake is only the the first step on the way to recovery from depression. The second and crucial step represents the feedback system, which can provide the continuous restoration of brain monoamines in the context of free search behavior. This feedback system on the one hand helps to overcome depression and on the other hand causes the hyposensitivity of the postsynaptic catecholamine (CA) receptors, due to the increased activity of the brain CA system. According to the search activity concept, REM sleep in the healthy subject, being a part of the same feedback system, restores brain monoamines. The mechanism of REM sleep deprivation in the treatment of depression is discussed in the context of this feedback system.

Effects of chronic ethanol consumption on gestation and lactation in rats

Abstract: Chronic consumption of ethanol during pregnancy and lactation may lead to abnormalities in the fetus or infant. A group of female Wistar rats was submitted to ethanol treatment over a period of a month. A pair-fed control group received sucrose solution isocaloric to ethanol and the control group received water “ad libitum.” Afterward, the females were mated with males over a period of 20 days. At birth, each litter was maximized to eight pups and the remaining ones were decapitated to remove the fetal blood and brains. No significant difference was observed in fetal body and brain weight at birth. During lactation the ethanol and pair-fed groups gained less weight than the control group. After weaning, their weight became similar. Fetal blood glucose levels were decreased in the ethanol-treated group. One hundred percent of the pair-fed and control females delivered live fetuses at term and all survived; only 40% of the females in the ethanol group delivered, and one pup did not survive. Chronic ethanol treatment pointed to a possible reduction in the fertility. It seems likely that the change in body weight of ethanol-fed dams was caused by undernutrition.

An account of consciousness in physical and functional terms: A target for research in the neurosciences

Abstract: The neurophysiology of mental events cannot be fully understood unless that of consciousness is understood. As the first step in a top-down approach to that problem, one needs to find an account of consciousness as a property of the biological organism that can be clearly defined as such. However, if it is to deliver what must be expected of it, it should address what is commonly meant by the wordconsciousness. Unless the last condition is satisfied, the theory will fail to deliver what must ultimately be expected of it.

Visual slow brain potentials in children with attention deficit disorder.

Abstract: Using a two-stimulus reaction time paradigm, with two separate reward conditions (contingent and noncontingent), we compared slow wave brain potentials (ERPs) in 144 children with attention deficit disorder (ADD) and 30 normal control children. This article reviews the findings during the 900 msec visual warning stimulus. As we had expected, based on ERP work of Forth and Hare (1989) and Raine, Venables and Williams (1990), and on previous work from our own laboratory, the group differences were found in the negative slow wave portions of the ERP complex during the contingent reward condition but not during the noncontingent condition. Aggressive hyperactive subjects with attention deficit disorder (ADDHA) were discriminated from nonaggressive subjects (including control subjects) during the contingent reward condition in the following ways: (1) greater fronto-central negativity (640–900 msec slow wave) and (2) greater right parietal than left parietal negativity (430–750 msec slow wave). All ADD subgroups, when compared to control (CONTR) subjects, showed greater slow wave negativity (700–900 msec) at the midline occipital electrode site during the contingent reward condition. This could be explained in part as an IQ effect on ERPs reflecting the IQ difference between the ADD subgroups and the controls. These slow wave findings seem to relate to attentional problems of these children. They are discussed in terms of a psychobiological model of inhibition/disinhibition and appetitive activation.

Diaphragmatic spasm: a neglected cause of dyspnoea and chest pain.

Abstract: The study included 17 patients, 12 women and 5 men, with a recurrent symptom complex involving chest pain and dyspnoea characterized by inability to get a full breath. Some attacks had subsided spontaneously. Others had lasted hours or days. When examined by fluoroscopy during an attack, each subject was found to have a nearly maximally contracted (flat) diaphragm. In some of them the attack was promptly interrupted by a small intravenous injection of sodium amytal. In others it could be aborted by a conscious effort at full expiration. The syndrome associated with diaphragmatic spasm is discussed in comparison with other noncardiac sources of chest pain and dyspnoea.

Brain asymmetry and autonomic conditioning: sensitization control.

Abstract: In the present experiment we report effects of cerebral asymmetry, or laterality, during classical conditioning to facial emotional stimuli. Twenty-five female subjects were presented with slides of a happy face in one visual half-field (VHF), and simultaneously a slide of an angry face in the other VHF, followed by shock as the unconditioned stimulus (UCS). To control for effects of sensitization, a new stimulus, never associated with the UCS, was introduced in the extinction phase. Dependent measures were phasic heart rate responses (HR) and skin conductance responses (SCR). The HR results showed a significant right hemisphere effect for the CS-UCS association, that was not attributable to UCS sensitization. No significant effects were found for the SCRs. The basic HR finding was a right hemisphere superiority for learning of a conditioned association.

Electrodermal Pavlovian conditioning with prepared and unprepared stimuli.

Abstract: One-trial learning referred to by Guthrie has been suggested to occur in autonomic conditioning, if the conditional stimuli (CSs) are so-called prepared ones. To test this idea, half of 28 subjects were given spider or snake slides as “prepared” CSs, while the remainder were given neutral slides as “unprepared” CSs. A shock was employed as the unconditional stimulus (UCS), with a CS-UCS interval of 8 seconds. Electrodermal activity and probe reaction times were the dependent measures of conditioning, conceived in cognitive, information-processing terms as the learning of the CS/UCS contingency. Evidence for the usual CS/UCS contingency learning emerged in both indicators, and during both acquisition and extinction, but none for one-trial learning, perhaps because the UCS was insufficiently aversive.

Gender, psychological well-being and somatic cardiovascular risk factors

Abstract: The purpose of this study is to determine associations between cardiovascular risk factors and subjective experience of psychological general well-being with special reference to gender related differences. One-hundred fifty white-collar workers in a car manufacturing plant in Sweden participated in a health care screening program. Subjective experience of psychological well-being was significantly correlated with cardiovascular risk factors among both men and women. There were, however, marked differences between the genders. For men, the following specific psychological variables were correlated with different cardiovascular risk factors: estimation of general health and psychological well-being, anxiety, depression, self-control and vitality. For women, more complex significant relationships between the two sets of variables were found. Moreover, the direction of the correlations differed between the genders. For example, men with cardiovascular risk factors, such as increased waist-hip-ratio, age and cholesterol, reported significantly more positive estimation of their self-control and vitality. For women the relation was the opposite with a significantly positive correlation (p=3D0.008) between experience of good health and a low risk factor profile indicating the concordance between physiological and psychological parameters. Possible reasons for these sex differences are discussed.

Psychoneurocardiology: psychosomatic and somatopsychic approaches to hypertension research.

Abstract: We introduce the field of psychoneurocardiology, and cite examples of research into psychosomatic and somatopsychic bases for hypertensive development. Beta-adrenergic hyperreactivity (a possible precursor of hypertension), as indexed by electrocardiographic T-wave amplitude suppression, was greater during active than passive coping tasks. The rise in tonic mean arterial blood pressure in normotensives over a 19-month period was a joint function of self-reported daily stress and baroreceptor-dependent pain dampening (as determined by the PRES method of noninvasive controlled carotid baroreceptor manipulation). The latter finding provides support for the learned model of hypertension. In this model, phasic blood pressure increases stimulate the baroreceptors, which in turn dampen pain and stress. The long-term effect of this relief is initially to increase the frequency of such phasic increases, and eventually to produce a tonic elevation in blood pressure.

The role of the central nervous system in sudden cardiac death: Heartbeat dynamics in conscious pigs during coronary occlusion, psychologic stress and intracerebral propranolol

Abstract: Electrocardiograms were recorded in conscious pigs during psychological stress (touching), left anterior descending coronary artery occlusion, intracerebral levo-propranolol (0.05 mg/kg), and their respective controls. The R-R intervals were evaluated with both a deterministic measure (point correlation dimension) and a stochastic one (mean). Only the deterministic measure was sensitive to between-subject responses (P<.01), whereas both measures were sensitive to within-subject changes. The results are explained by a deterministic model of heartbeat generation.

Involvement of cardiac, respiratory and gastrointestinal functions in neural responses to stressful events.

Abstract: In the stress concept, fight and flight situations as well as other CNS-controlled reaction patterns for alertness to danger have to be followed by or integrated with a restorative “build-up” process in order to maintain homeostasis. The “build-up” process can be studied physiologically for example after regular exercise or training. Under these conditions there is a decrease in resting sympathetic adrenergic activity and an increase in the parasympathetic vagal activity.

E-wave and heart rate responses during anticipation of nonmotor events.

Abstract: This study concentrated on three main questions: 1) can anticipatory late negative shift (expectancy wave, E-wave) be elicited in nonmotor S1-S2 paradigm, 2) is it sensitive to variation of emotional aspects of the task and 3) is there a connection between heart rate (HR) responses and E-wave. S1 was a letter row that was replaced tachistoscopically by another letter row (S2). The task of the subjects (n = 12) was to detect if the critical aspects of S2 were similar to S1. After their delayed response they received feedback of their performance. The emotional aspects of the task were varied by presenting aversive noise bursts at the end of the feedback period either always, contingently to their performance or not at all. A negative shift was present both before S2 and aversive noise (when presented). Varying the emotional aspects of the task had an effect on the amplitude of the E-wave. There was also a connection between E-wave and heart rate responses: heart rate response seemed to be a precondition for E-wave elicitation. The results support Simons's conclusion that nonmotor E-wave reflects specifically emotional anticipation.