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Biomedical subjects

J E Skinner

Publications and source records attributed to J E Skinner.

At least 19 recordsLinked to original sources
PubMed1997

Dimensional complexity of the EEG in subcortical stroke--a case study.

The conventional electrophysiological methods used for the analysis of the functional characteristics of the nervous system are not able to grasp its non-linear and random features. Of the methods based on the application of chaos-theory the correlation dimension analysis can be used to quantify the complexity of the analyzed signal, such as the electroencephalogram (EEG). The new version (point-correlation dimension, PD2) was used in this study, which is more accurate than the other, currently used algorithms. The purpose of the present investigation was to compare the sensitivity of the methods based on chaos-theory with the traditional electrophysiological ones in a case when no apparent abnormality was present as judged on the basis of this latter methodology. The PD2 was calculated from the EEG recorded in 13 healthy control subjects and in a patient who suffered a small subcortical stroke 2 years prior to the investigation and who was free of neurological symptoms at the time of recording. Compared to that seen in the control group, in the Z-score maps of the scalp distribution of the PD2, a marked asymmetry was seen and the absolute PD2 values showed a low-dimensional area in the parietal region, ipsilateral to the stroke. A relative decrease of the gamma band was found in the frequency power spectra in the same area. It is suggested that the additional information extracted from the EEG by non-linear analysis may increase the sensitivity of electrophysiological methods for detecting brain pathology.

Algorithms↗
PubMed1995

Correlation dimension changes accompanying the occurrence of the mismatch negativity and the P3 event-related potential component.

The aim of this study was to apply recently developed mathematical tools of chaos theory to the analysis of event-related potentials (ERPs) recorded in paradigms in which the mismatch negativity (MMN) and the P3 component appeared. A new method, the point correlation dimension (PD2i), was used for data analysis, which is more accurate than other algorithms for the calculation of the correlation dimension (D2), which latter is a measure of the complexity of the generator(s) responsible for producing the analyzed time series, i.e., the EEG. ERPs were recorded from Fz, Cz and Pz in 6 subjects. With respect to baseline, the PD2i decreased significantly both during the event-related potentials in which the MMN and also in which the P3 was present, but the pattern and magnitude of this decrease was different between these two situations. The pattern of PD2i changes during the occurrence of deviant stimuli eliciting the MMN suggests the presence of a frontal MMN generator. The conspicuous PD2i decrease during the occurrence of the P3 wave may support the "context closure" hypothesis concerning its functional significance.

Acoustic Stimulation↗
PubMed1994

Low-dimensional chaos in biological systems.

During the past five years general rules have been developed for the application of chaos theory to biology and medicine, which enable investigators to avoid the pitfalls that invalidated and trivialized many earlier results. The importance of biological chaos is that the variables governing the spatial and temporal geometries of the system may be few in number, fractional in dimension, and thus enable low-energy control with complex deterministic consequences. The complexity of control inherent in chaotic systems may be important in the dynamics of gene expression and translation. Extending these ideas may lead to completely novel ways to modulate protein production by introducing simple pulses at critical times or places.

Algorithms↗
PubMed1994

Chaos and physiology: deterministic chaos in excitable cell assemblies.

In this review we examined the emerging science of deterministic chaos (nonlinear systems theory) and its application to selected physiological systems. Although many of the popular images of fractals represent fascination and beauty that by analogy corresponds to nature as we see it, the question remains as to its ultimate meaning for physiological processes. It was our intent to help clarify this somewhat popular, somewhat obscure area of nonlinear dynamics in the context of an ever-changing procedural base. We examined not only the basic concepts of chaos, but also its applications ranging from observations in single cells to the complexity of the EEG. We have not suggested that nonlinear dynamics will answer all of our questions; however, we did attempt to illustrate ways in which this approach may help us to answer new questions and to rearticulate old ones. Chaos is revolutionary in that the overall approach requires us to adopt a different frame of reference which, at times, may move us away from previous concerns and methods of data analysis. In sections I-IV, we summarized the nonlinear dynamics approach and described its application to physiology and neural systems. First, we presented a general overview of the application of nonlinear dynamical techniques to neural systems. We discussed the manner in which even apparently simple deterministic systems can behave in an unpredictable manner. Second, we described the principles of nonlinear dynamical systems including the derived analytical techniques. We now see a variety of procedures for delineating whether frenetic chaotic behavior results from a nonlinear dynamical system with a few degrees of freedom, or whether it is caused by an infinite number of variables, i.e., noise. Third, we approached the applications of nonlinear procedures to the cardiovascular systems and to the neurosciences. In terms of time series, we described initial studies which applied the now "traditional" measures of dimensionality (e.g., based on the algorithm by Grassberger and Procaccia) and information change (e.g., Lyapunov exponents). Examples include our own work and that of Pritchard et al., demonstrating that the dynamics of neural mass activity reflect psychopathological states. Today, however, the trend has expanded to include the use of surrogate data and statistical null hypotheses testing to examine whether a given time series can be considered different from that of white or colored noise (cf. Ref. 262). One of the most important potential applications is that of quantifying changes in nonlinear dynamics to predict future states of the system.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1993

A reduction in the correlation dimension of heartbeat intervals precedes imminent ventricular fibrillation in human subjects.

Reduced reflexive control of heartbeat intervals occurs with advanced heart disease and is an independent risk factor for mortality. Based on a previous study of experimental myocardial infarction in pigs, we hypothesized that a deterministic measure of heartbeat dynamics, the correlation dimension of R-R intervals (D2), may be a better predictor of risk than a stochastic measure, such as the standard deviation (SD). We determined the point estimates of the heartbeat D2 (i.e., PD2s) in Holter electrocardiographic recordings from 11 high-risk patients who manifested ventricular fibrillation (VF) during the recording and in high-risk controls having only nonsustained ventricular tachycardia (14 patients) or premature ventricular complexes (13 patients). We found that PD2 reduction (i.e., PD2s < 1.2) precedes lethal arrhythmias by hours, but is not reduced in high-risk controls (p < 0.001; sensitivity, 91%; specificity, 85%). Heartbeat SD did not discriminate among the patients. Thus PD2 of heartbeat intervals may provide an important diagnostic test and early warning sign of VF.

Algorithms↗
PubMed1993

Conventional heart rate variability analysis of ambulatory electrocardiographic recordings fails to predict imminent ventricular fibrillation.

OBJECTIVES: The purpose of this report was to study heart rate variability in Holter recordings of patients who experienced ventricular fibrillation during the recording. BACKGROUND: Decreased heart rate variability is recognized as a long-term predictor of overall and arrhythmic death after myocardial infarction. It was therefore postulated that heart rate variability would be lowest when measured immediately before ventricular fibrillation. METHODS: Conventional indexes of heart rate variability were calculated from Holter recordings of 24 patients with structural heart disease who had ventricular fibrillation during monitoring. The control group consisted of 19 patients with coronary artery disease, of comparable age and left ventricular ejection fraction, who had nonsustained ventricular tachycardia but no ventricular fibrillation. RESULTS: Heart rate variability did not differ between the two groups, and no consistent trends in heart rate variability were observed before ventricular fibrillation occurred. CONCLUSIONS: Although conventional heart rate variability is an independent long-term predictor of adverse outcome after myocardial infarction, its clinical utility as a short-term predictor of life-threatening arrhythmias remains to be elucidated.

Adult↗
PubMed1993

Neurocardiology. Brain mechanisms underlying fatal cardiac arrhythmias.

Chaos theory may have a widespread application in medicine, from the analysis of protein structure at one end of the spectrum to fetal monitoring and the measurement of aging on the other. This application is especially on firm ground in cardiology, where it is simple and precise for the experimenter, and a primer exists for the clinician. As just presented, the point-correlation-dimension analysis of heartbeat variability is able to characterize the patterns of low-dimensional chaos produced by the heartbeat generator, a mechanism that is a composite of the voltage-dependent, neurotransmitter-dependent, and circulation-dependent ionic conductances that are all located in the myocardium where the heartbeat is formed. Most importantly, this deterministic measure of heartbeat variability is able to predict imminent lethal arrhythmogenesis with an accuracy that the more familiar stochastic measures do not have. This may arise because the PD2 is sensitive to the net degrees of freedom of the heartbeat generator, which, under the influence of the nerves and the coronary circulation, can be shifted so the resulting dynamics cause the initiation of lethal arrhythmogenesis. Application of chaos theory in neurology may be equally fruitful because the deterministic measures can discriminate among neuronal firing patterns, reveal subtle changes in brain waves, and be related to higher cognitive processes. Psychiatry also seems quite likely to benefit more and more from the application because the algorithms can discriminate schizophrenic brain functions from normal ones. Thus it can be expected that future applications will enable observation of biologic processes all along the brain-heart axis by which lethal ventricular fibrillation is regulated and perhaps even caused by its determination of the heartbeat dynamics. The subfield of neurocardiology has come a long way since it was first positively identified as an important research area. It took a lot of experiments to show how lethal cardiac arrhythmogenesis is involved with cerebral activities delivered over autonomic pathways. Although we do not yet fully understand the causal mechanism of lethal arrhythmogenesis, we may be getting close. It will become increasingly imperative for the clinical neurologist, along with the cardiologist, to understand the importance of neurocardiology in medical therapy and for the neurologist, along with the cardiologist and psychiatrist, to understand its importance in preventive treatments.

Animals↗
PubMed1992

Cryoblockade in limbic brain (amygdala) prevents or delays ventricular fibrillation after coronary artery occlusion in psychologically stressed pigs.

Neomammalian and paleomammalian (limbic) brain structures control different behaviors and the autonomic support specific to each. Both neural systems are involved in cardiovascular disorders. Our previous studies showed that bilateral cryoblockade of a neomammalian structure (the frontal lobes) reduces blood pressure elevations in experimental hypertension and prevents lethal arrhythmogenesis in experimental myocardial infarction. Other studies showed that bilateral lesions in a paleomammalian structure (amygdala) also reduce the blood pressure elevations. Thus, we hypothesized that cryoblockade of the amygdala would prevent lethal arrhythmogenesis. We found that cooling of cryoprobes implanted bilaterally in the amygdala prevented ventricular fibrillation in five of eight pigs during a 20-minute period of reversible myocardial ischemia, whereas cryoblockade in structures surrounding the amygdala (five pigs), unilateral cryoblockade in the amygdala (two pigs), or sham operations (three pigs) did not prevent ventricular fibrillation (p less than 0.003). In two of the five pigs with amygdaloid blockade, the cooling was reversed at 20 minutes while the coronary occlusion continued (24 hours), and still ventricular fibrillation did not occur. In all other cases, ischemia was reversed at 20 minutes so that the heart could recover; this enabled histochemical documentation that the heart was normal at the time(s) ischemia was induced, and it allowed within-subject control experiments. Amygdaloid cryoblockade produced a small but significant increase in heart rate (10 beats per minute) without a change in blood pressure. We conclude that the paleomammalian brain, like its neomammalian counterpart, mediates brain effects on fatal arrhythmogenesis.

Amygdala↗
PubMed1992

Low-dimensional chaos in event-related brain potentials.

The quantification of a chaotic system, such as the nervous system, can be made by calculating the correlation dimension (D2) from a sample of the data it generates. The encephalogram was recorded from the vertex during an auditory "odd-ball" paradigm and was signal-averaged to reveal the event-related potentials (ERPs). A new method for continuously estimating D2, the "Point-D2" (PD2), was determined from the same data, and it also was signal-averaged. The PD2 method was found to be more accurate than others currently used for investigating finite data; it also was found to track nonstationarities that arise within the data. A significant (p < .001) PD2-decrease accompanied the ERPs evoked by target stimuli; the PD2 onset-latency and peak did not correlate with any ERPs. The very short latency suggests that the PD2-decrease may be associated with "selective stimulus set," an interpretation that has been related to early cortical ERP components.

Acoustic Stimulation↗
PubMed1991

Correlation dimension of heartbeat intervals is reduced in conscious pigs by myocardial ischemia.

A reduced standard deviation of RR intervals (SDRR) predicts increased mortality in groups of survivors of myocardial infarction. Like SDRR, the correlation dimension (D2) describes variation within a sampled time series, but uniquely it reveals 1) the epoch's geometric structure and 2) the degrees of freedom of the generator. These unique features may be more sensitive predictors of mortality than SDRR. We developed a new algorithm for estimating D2 (i.e., the "point-D2"), tested it with known data, and found that it had greater accuracy for finite data than other published algorithms. Analysis of RR intervals from eight conscious pigs undergoing acute occlusion of the left anterior descending coronary artery revealed a drop in the point-D2 from a control mean and standard deviation of 2.50 +/- 0.81 to 1.58 +/- 0.64 during the first minute of ischemia (p less than 0.01) and to 1.07 +/- 0.18 during the last minute preceding ventricular fibrillation (p less than 0.01). Partial occlusions (50-90% reduction of coronary blood flow) evoked point-D2 reductions only 25-30% of control (p less than 0.01). The point-D2 means were correlated between pigs with the magnitude of the respiratory sinus arrhythmia (p less than 0.01), but during ischemia this correlation was replaced by one between the standard deviation of the point-D2s and SDRRs. Because the simultaneous reduction in the mean point-D2 and its standard deviation to 1.07 +/- 0.18 occurred in every case, was unique to the few minutes preceding ventricular fibrillation, and never reached these low values during other conditions in which it was reduced, we conclude that the point-D2 may be an accurate prospective predictor of mortality within the individual subject.

Algorithms↗
PubMed1991

Coronary flow and mental stress. Experimental findings.

The hemodynamic, electrocardiographic, and coronary flow responses to a psychological test were studied in 13 pigs both in the absence (group 1, n = 8) and the presence (group 2, n = 5) of a transient occlusion of the left anterior descending coronary artery. The psychological test consisted of presenting food to a fasting but restrained animal for 3 minutes. In group 1, stress increased the heart rate from 128 +/- 5 to 176 +/- 8 beats/min (mean +/- SEM) and arterial pressure from 93 +/- 4 to 112 mm Hg. Comparing the individual increase in rate-pressure product with the increase in coronary conductance during the test, a parallel response was found in only two animals, whereas a relatively lower coronary conductance was observed in the remainder, suggesting vasoconstriction. Clinical signs of ischemia or life-threatening arrhythmias were never observed in this group of animals. Each group 2 animal underwent two occlusions of the left anterior descending coronary artery, randomly performed on separate days both in the presence and the absence of the food deprivation stress. When the latter was applied in the presence of occlusion, all animals developed ventricular fibrillation in less than 2 minutes (mean, 81.4 seconds). Conversely, only one animal had ventricular fibrillation when a 3-minute occlusion was performed without exposure to stress. This occurred despite the fact that more severe ischemia (as detected by an increase in left ventricular end-diastolic pressure and decreases in dP/dt and systolic pressure) was recorded at 3 minutes of occlusion.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1990

Central beta-adrenergic mechanisms may modulate ischemic ventricular fibrillation in pigs.

A central noradrenergic process may permit expression of the stress-related increase in cardiac vulnerability to ventricular fibrillation (VF). Thus, the effect of central beta-adrenergic receptor blockade with L-propranolol (0.01 and 0.05 mg/kg) on ischemia-induced VF vulnerability was evaluated in the psychologically stressed pig model and compared with Ringer's solution and D-propranolol (0.05 mg/kg). The ischemia of a maximum 15-minute left anterior descending coronary artery occlusion was used since we previously determined that pigs surviving 15 minutes usually do not fibrillate. Time to the onset of VF was analyzed by time-to-event analysis and ranged from 0.75 to 13.8 minutes in vulnerable pigs. Intracerebroventricular administration of L-propranolol (0.05 mg/kg) prolonged the time to VF compared with Ringer's solution and D-propranolol (p less than 0.05). The high dose of L-propranolol also reduced the incidence of VF (7/15 fibrillated) compared with Ringer's solution (12/12 fibrillated) and D-propranolol (6/7 fibrillated). The lower dose of L-propranolol was without effect on VF vulnerability (7/9) fibrillated). The plasma concentration resulting from central administration of 0.05 mg/kg L-propranolol was found to be 9.05 +/- 3.25 ng/ml, which is significantly below therapeutic antiarrhythmic blood levels. We conclude that the reduced vulnerability to ischemia-induced VF after intracerebroventricular administration of propranolol is due to alteration of a central beta-adrenergic receptor-mediated phenomenon as opposed to an effect on the heart directly or to nonspecific membrane stabilization.

Adaptation, Physiological↗
PubMed1988

Centrifugal regulation of neuronal activity in the olfactory bulb of the waking rabbit as revealed by reversible cryogenic blockade.

The influences of centrifugal projections to the olfactory bulb were examined on the bulbar EEG and mitral-tufted cell activity in waking rabbits. Each of 6 rabbits was implanted, under surgical anesthesia, with fine wire electrodes for recording of the EEG and mitral-tufted cell unit activity and for stimulating the lateral olfactory tract. Two cooling probes, for reversible cryogenic blockade, were implanted on either side of the left olfactory peduncle. Records of EEG and unit activity were taken for 200 s before, during and after cooling of the probes to 3 degrees centigrade. Antidromic evoked potentials were used to assess the efficacy of the blockade. During the cryogenic blockade bursts of EEG activity, evoked in the bulb by inspiration through the nose, were augmented in amplitude and reduced in frequency. Mitral-tufted cell unit activity was reduced in rate but was more highly correlated with the phase and amplitude of the EEG bursts. Analysis of individual EEG bursts revealed that the variance in frequency of bulbar activity was significantly reduced in the isolated state. The data demonstrate that oscillatory bursting activity in the olfactory bulb is intrinsically maintained within a relatively fixed frequency range during receptor input and does not depend on centrifugal projections for its electrogenesis. Changes in EEG frequency, amplitude and correlation with unit activity support the hypothesis that centrifugal projections act in part to inhibit mitral-tufted cell output by direct excitation of granule cells. These findings are supported by a theoretical model in which distributed feedback to the granule cells from more central olfactory structures acts to regulate the coherency of bulbar activity.

Action Potentials↗
PubMed1988

Field potential response changes in the rabbit olfactory bulb accompany behavioral habituation during the repeated presentation of unreinforced odors.

Experiments were performed on waking rabbits to investigate the changes in both sniffing behavior and local field potential responses in the olfactory bulb during repeated exposure to unreinforced odors. Six rabbits were each implanted with 2 pairs of electrodes for differential recording of the bulbar extracellular field potential. Each animal was given 3 sequential sessions to each of 2 separate odors on 6 consecutive days, while monitoring the bulbar field potential activity and sniffing behavior. Behavioral sniffing responses exhibited rapid within-session decrement in amplitude and long term decrement across sessions. The within-session decrement showed spontaneous recovery between sessions. Both decremental changes in sniffing behavior were accompanied by changes in the bulbar field potential responses. The responses to novel odors were characterized by a reduction in amplitude of high frequency activity (40-80 Hz) and a corresponding increase in amplitude of low frequency activity (15-25 Hz). The high frequency component of the responses showed an initial increase in frequency to a novel odor on the first 3 presentations followed by a rapid decrease in frequency on subsequent trials in the first session which stabilized thereafter. No change in frequency or relative amplitude was observed for the low frequency component. The absolute difference between the odor evoked activity and the preceding control activity measured on each trial showed a significant decrement across sessions with no evidence for spontaneous recovery. The results demonstrate that olfactory bulb responses to novel unreinforced odors show both rapid and long-term changes which parallel changes in sniffing behavior.(ABSTRACT TRUNCATED AT 250 WORDS)

Action Potentials↗
PubMed1987

Induction and maintenance of epileptiform activity in the rabbit olfactory bulb depends on centrifugal input.

A technique of cryogenic blockade was used in waking rabbits to produce complete and reversible isolation of the olfactory bulb from the rest of the brain. During cooling of the olfactory peduncle epileptiform activity occurred spontaneously in the pyriform cortex in 3 out of 20 sessions, but never in the bulb. Following removal of the cryoblockade, during the seizure state, epileptiform discharges appeared simultaneously in the bulb and pyriform cortex. In the control state, without cooling of the peduncle, epileptiform activity could be evoked in the bulb and cortex by intense electrical stimulation of either the bulb or the lateral olfactory tract. During the cryoblockade, however, intense stimulation of the bulb failed to evoke seizure-like discharges. The results demonstrate a dependency on more central olfactory structures for the induction and maintenance of epileptiform activity in the olfactory bulb.

Animals↗
PubMed1987

Cryoblockade of the ventromedial frontal cortex reverses hypertension in the rat.

The anteroventral part of the hypothalamus adjacent to the third ventricle (AV3V) has been implicated in electrolytic lesion studies as a site crucial to the development and maintenance of hypertension. Cryoblockade is known to alter synaptic and axonal transmission differently at different temperatures. In this study, cooling of the hypothalamus, including the AV3V area, to the temperature known to block only synaptic function did not alter blood pressure in two different models of experimental hypertension in the rat. Cooling sufficient to block both synaptic and axonal transmission, however, reduced blood pressure elevations to near normotensive levels. Synaptic cryoblockade in the ventromedial portion of the frontal cortex lowered experimental hypertension by 21 +/- 3 mm Hg (p less than 0.05). In normotensive controls, blood pressure was not altered by cryoblockade in either the frontal cortex or hypothalamus. Anatomical evidence provided by others shows that cells in the ventromedial frontal cortex project, in part, through the AV3V region to the brainstem cardioregulatory structures. These results indicate that neural activity arising in frontal cortex is axonally projected through the hypothalamus to maintain elevated blood pressure in experimental hypertension.

Animals↗