Interval Plots Research Articles

Distribution-free graphical and statistical analysis of serial dependence in neuronal spike trains

Two-dimensional ‘joint’ interval distributions of sequential interspike intervals (ISIs) are a commonly used tool in neuronal spike train analysis. We present and evaluate here a modification of the joint interval plot using ranked ISIs. This modification provides clearer graphical evaluation of serial dependence in ISI sequences, a distribution-free basis for isolating changes in serial dependence across experimental treatments from changes in ISI distributions, and a basis for unambiguous statistical tests of serial dependence and stationarity. To validate this method and illustrate the advantages of its use we have applied it to both single-neuron spike trains recorded from cultured mammalian spinal cord neurons and artificial spike trains generated by stochastic models with defined burst envelopes and serial dependencies.

Efficacy of two Pyrethroids Against Bollworms Under a Traditional and an Extended Spray Interval Approach in Southern North Carolina, 1994

Abstract Cotton was planted on 25 Apr in a Marlboro sandy loam soil near Johns, NC, in Scotland County. Recommended practices for fertility and weed control were followed and 0.75 lb (AI)/acre Temik 15G was used at planting for thrips. A RCBD with 5 replicates and 6-row (38 inch centers) × 50 ft plots with 8 ft alleys were utilized. Treatments were applied with a backpack CO2- pressurized sprayer calibrated to deliver 8.0 gpa at 50 psi. Initial application for all treatments, based upon exceeding a threshold of 10 eggs per 100 terminals, was made on 17 Jul. The second application for the Baythroid 0.028 lb (AI)/acre, ‘start only’ treatment was made on 22 Jul, while the Baythroid at 0.045 lb (AI)/acre regular start treatment received only the initial application. The Baythroid at 0.028 lb (AI)/acre, scouting-based plot was treated on 17, 22 Jul, 4 and 24 Aug. The Baythroid at 0.045 lb (ALVacre, extended, 14-d interval plot was treated on 17, 31 Jul, 14 and 24 Aug. A final Baythroid 0.028 lb (AI)/acre, extended, 14-d interval treatment was likewise treated on 17, 31 Jul, 14 and 24 Aug. Karate at 0.025 lb (AI)/acre was treated at the scouting-based schedule of 17, 22 Jul, 4 and 24 Aug, and the same material at 0.04 lb (AI)/acre on the extended 14-d interval was applied on 17, 31 Jul, 14 and 24 Aug. Twenty five bolls in all plots were evaluated for BW damage and live larvae on 28 Jul and 11 Aug and for both BW and ECB-damaged bolls and live larvae on 7 Sep. Data were subjected to ANOVA and DMRT.

Differentiation of sinus tachycardia from ventricular tachycardia with 1:1 ventriculoatrial conduction in dual chamber implantable cardioverter defibrillators: feasibility of a criterion based on the atrioventricular interval.

Tachycardia discrimination in future implantable cardioverter defibrillators (ICDs) is likely to be enhanced by the addition of an atrial sensing/pacing lead. However, differentiation of sinus tachycardia (ST) from ventricular tachycardia (VT) with 1:1 VA conduction will remain problematic. We assessed the use of the AV interval as a potential criterion for correctly differentiating ST from VT. Incremental V pacing at the right ventricular (RV) apex served as a "VT" model in each of 41 patients with 1:1 VA conduction to pacing cycle lengths < or = 450 msec. High right atrial and RV apical electrograms during normal sinus rhythm (NSR) and during incremental V pacing were digitized (simulating ICD sensing). From these signals, AV interval versus pacing cycle length plots were computer generated to identify crossover cycle lengths, each defined as the cycle length at which the AV interval during V pacing equals the AV interval during NSR. At cycle lengths longer than the crossover value, the AV interval during "VT" exceeds the AV interval during NSR. In contrast, the AV interval during ST is physiologically shorter than the AV interval during NSR. Thus, ST can be readily differentiated from "VT" over a range of cycle lengths greater than the crossover value. The overall mean calculated crossover cycle length was 371 +/- 52 msec. In 11 patients paced multiple times, each crossover cycle length was reproducible (mean coefficient of variation was 1.2% +/- 0.9% per patient). AV intervals measured at the RV apex were also analyzed with incremental V pacing during catecholamine stimulation (isoproterenol, n = 5) and during alternate site "VT" (RV outflow tract [n = 8] and left ventricle [n = 2]). In all these cases, the new "VT" plots of AV interval versus pacing cycle length coincided with or fell to the left of those obtained during control RV apical pacing and recording (i.e., these AV interval values crossed the NSR baseline at cycle lengths < or = the crossover cycle length). Thus, the cycle length range for recognizable differentiation of ST from "VT" remained valid. The data suggest that the described AV interval criterion relying on the crossover cycle length: (1) is a promising approach to improve differentiation of ST from relatively slow VTs with 1:1 VA conduction, and (2) can readily be automated in future dual chamber ICDs, given its computational simplicity.

The dynamic range of neonatal heart rate variability.

Although it is generally appreciated that heart rate variability is low during severe illness, the extent, time course, and mathematical characteristics of heart rate variability during transitions between health and illness have not been systematically examined. The purpose of this study was to analyze heart rate variability in newborn infants during a rapid recovery from severe respiratory and circulatory failure. From prolonged ECG recordings, we evaluated heart rate variability in the time domain (mean, relative change, and coefficient of variation of RR intervals), in the frequency domain (using power spectra of the time series of RR intervals), and using a neural network. Qualitatively, RR interval plots showed little heart rate variability during severe illness but became "noisier" during recovery. Quantitatively, recovery was marked by twofold to threefold increases in time-domain parameters, by eightfold increases in frequency-domain parameters, and by more than 20-fold increases in a neural network measure. Time-domain and frequency-domain measures were correlated, but not strongly. Heart rate variability reached stable levels by 4 to 5 days. Heart rate did not change dramatically. Recovery from severe neonatal illness is accompanied by large and rapid increases in heart rate variability, but not by large changes in heart rate. This increase can be effectively assessed in the time domain, in the frequency domain, and by using a neural network.

Postnatal changes in the dorsal root reflex in the isolated spinal cord of the hamster, Mesocricetus auratus

Spontaneous activity has been demonstrated in the lumbar dorsal roots of isolated spinal cord preparations taken from animals ranging in age from 2 to 65 days. Peaks of activity were recorded at 2 and 5 weeks of age, with mean firing frequencies of 33 Hz and 28 Hz respectively. The firing frequency in weeks 3 and 4 was lower (15 Hz) as was the frequency in cords taken from animals older than 6 weeks. The pattern of the spontaneous dorsal root activity changed during the first 5 weeks of life. In cords taken from animals less than 10 days old, the roots fired single action potentials, producing a single broad peak in Inter Spike Interval plots (ISI). Dorsal root recordings made from cords taken from animals in weeks 2 and 3 of life exhibited both single spikes and bursts of action potentials. By the end of the third week of life, individual spike activityhad declined and the bursts of action potentials characteristic of the adult pattern had become dominant, producing a bimodal ISI plot. Cross correlation analysis of dorsal root and dorsal horn activity in lumbar segments up to five segments apart, revealed an increasing degree of correlation developing over the first 4 weeks of postnatal life. Dorsal horn responses to dorsal root stimulation in cords taken from young animals were prolonged, lasting in excess of 250 msec. In the third week of life, the duration of the excitatory component of the response was reduced to approximately 50 msec by the development of an inhibitory phase.

Efficacy of two Pyrethroids Employed at Traditional and Extended Spray Intervals Against Fall Armyworm, Bollworm and European Corn Borer in North Carolina, 1993

Abstract Cotton was planted in a Wagram loamy sand on 10 May near Richlands, NC. The fertility and weed management programs followed NCSU recommendations with 0.6 lb (AI)/acre Temik 15G applied in furrow at planting. Plot size was 6 rows (38 inch centers) × 50 ft with 10 ft alleys. A RCBD was used with 4 replicates. Treatments were applied via a backpack-type CO2-pressurized sprayer calibrated to deliver 8 gpa at 50 psi with a single TX-8 Spraying Systems nozzle per row. Initial application for all treatments, based upon exceeding a threshold of 10 eggs per 100 terminals, was made on 22 Jul. The second application for the Baythroid 0.028 lb (AI)/acre, regular start treatment was made on 27 Jul, while the Baythroid at 0.045 lb (AI)/acre regular start treatment received only the initial application. The Baythroid at 0.028 lb (AI)/acre, scouting-based plot was treated on 22 and 27 Jul and on 4 and 19 Aug. The Baythroid at 0.045 lb (AI)/acre, extended, 14-d interval plot was treated on 22 Jul and on 4 and 19 Aug. A final Baythroid 0.028 lb (AI)/acre, extended, 14-d interval treatment was likewise applied on 22 Jul and on 4 and 19 Aug. Karate at 0.025 lb (AI)/acre was also treated at a scouting-based schedule of 22 and 27 Jul and 4 and 19 Aug, and the same material at 0.04 lb (AI)/acre on the extended 14-d interval was applied on 22 Jul and on 4 and 19 Aug. All plots were evaluated for FAW, ECB and BW-damaged bolls on 17 Aug and 15 Sep. Plots were harvested with a 1-row John Deere mechanical picker from the middle two rows on 13 Oct.

Soil Chemistry in a Loblolly/Longleaf Pine Forest with Interval Burning.

We examined the 30-yr cumulative effects of prescribed fires at intervals of 1, 2, 3, and 4 yr in a loblolly and longleaf pine forest in the Coastal Plain of South Carolina. The fine fraction of the forest floor (Oe + Oa horizons) contained much more carbon and nitrogen per unit area in the control plots (1.7 and 0.05 kg/m2 , respectively) than in the 1-yr burn interval plots (0.4 and 0.007 kg/m2 , respectively). Mineral soils (0-0.2 m depth) were highly variable in chemistry, and showed only slight differences across the burning treatments for nitrogen and sulfur. No trends were apparent for phosphorus in the forest floor or mineral soil; differences in acidity and extractable cations were also slight. The nutrient content of foliage was generally low, with no differences across burning intervals. Our results are consistent with earlier studies that showed the biogeochemical effects of repeated surface fires in southern pine forests are generally limited to the forest floor, with the possible exception of overall reductions in nitrogen cycling.

Directional differences in excitability and margin of safety for propagation in sheep ventricular epicardial muscle.

Computer simulations and isolated tissue experiments were used to characterize the relation between excitability and margin of safety for propagation in anisotropic ventricular myocardium. Longitudinal, uniform transverse, and nonuniform transverse tissue directions were modeled in a one-dimensional Beeler-Reuter based cable. Stimulation threshold was smallest in the nonuniform transverse direction. The safety factor for propagation was determined in the model as the total axial charge that was available for depolarizing downstream tissue divided by the threshold charge that was just sufficient for continued propagation and was largest in the longitudinal direction. The strength-interval plot for the junction between simulated longitudinal and nonuniform transverse directions identified a range of stimulus strengths and intervals that resulted in nonuniform transverse but not longitudinal propagation. When high values of transverse resistance were used, higher stimulus strengths during premature stimulation resulted in longitudinal but not nonuniform transverse propagation. The experimental strength interval plots from 17 L-shaped preparations of isolated sheep epicardial muscles had similar characteristics. In nine additional L-shaped tissue experiments, changing extracellular K+ concentrations from 4 to 20 mM resulted in progressive membrane depolarization and conduction impairment in both directions. However, in eight of nine experiments, complete block occurred first in the transverse direction. In one experiment, block was simultaneous in both directions. We conclude that, under normal conditions, threshold requirements for active propagation are lower for transverse than for longitudinal propagation. In addition, when active membrane properties are impaired, the safety factor for propagation is larger in the direction along the longitudinal axis of the cells.

Arrhythmia analysis by successive RR plotting

A successive RR interval plot was developed to analyze arrhythmia. The plot consisted of a set of points with the x-value of (N)th RR interval and the y-value of (N + 1)th RR interval. This method was applied in the arrhythmia analysis of Holter electrocardiograms obtained from 35 patients. In the analysis of ventricular premature contractions (VPCs) this method was useful not only in detecting VPCs but also in demonstrating coupling interval-dependent characteristics of VPCs. In the analysis of atrial fibrillation the successive RR plot enabled the authors to estimate the functional refractory period of the atrioventricular conduction. In conclusion, despite its simplicity, the successive RR plot was found to be powerful in analyzing arrhythmia. Specifically, the potential to analyze integrally the coupling interval-dependent properties of various types of arrhythmia makes it attractive as a clinical tool.

The sequential-interval state space: a means of displaying temporal information in neuron firing

Variability in neuronal firing exhibits sufficient uncertainty so that a simple average firing frequency code is probably inadequate for most nervous system signalling. Temporal patterns certainly play an important role in neuronal coding. We have used interval histogram and 3-dimensional sequential interval state space plots to investigate various common patterns of firing in neurons of the land snail, Helix aspersa. Typical firing patterns included random, highly regular, doublet, and burst firing. Individual neurons could be made to change their temporal firing pattern in response to changes in transmembrane currents, or temperature, or the application of convulsant drugs. In every instance, the sequential interval state space plot provided a more distinctive display of temporal pattern than did the more common interval histogram. State space plots were also investigated for evidence of a predicted chaotic attractor. In no instance was this type of state space plot observed.

Profiles of instant heart rate during partial seizures

Instant heart rate (R-R intervals) can be readily studied during spontaneous seizures recorded with ambulatory cassette AEEG/AECG techniques. Ninety-three seizures were recorded in 32 patients with complex partial epilepsy. Instant R-R interval plots showed that 74% of seizures were associated with a dominant tachycardia, the most characteristics features of which were the initial steep acceleration phase at at seizure onset and the wide fluctuations in heart rate (‘exaggerated sinus arrhythmia’) which occurred during and immediately after the seizure. Five percent of seizures were associated with a dominant but transient phase of heart rate slowing during or towards the end of the seizure. Nineteen percent of seizures showed equivocal or negative ictal effects on the heart rate and rhythm despite unequivocal AEEG seizure discharges. Conversely, other patients had characteristic heart rate changes despite equivoval AEEG abnormality. The heart rate profiles showed striking seizure-to-seizure similarities when multiple fits were recorded in the same patient. Ratemeter profiles may be clinically useful to locate epileptic seizures in long duration records; they can help to locate seizures which are either inaccurately timed or poorly identified by the event marker, or not clearly associated with definite AEEG changes. The secondary cardiac effects of epilepsy may be misdiagnosed if their primary cerebral origin is not suspected.

Yield and persistence of irrigated lucernes cut at different frequencies, at Tamworth, New South Wales.

Three irrigated lucerne cultivars, Pioneer Brand 545 (winter dormant), Condura 73 Brand (semiwinter dormant), and CUF 101 (highly winter active), were harvested at fixed cutting intervals of either 25, 28 ,35, 42 or 48 days from September to April in each of four years. This paper reports the effects of these cutting frequencies on the dry matter yield, leaf to stem ratio and persistence of these cultivars. The effect of cutting frequency on mean total yield (the sum of the mean yields for each harvest) was significant (P&lt;0.05) in each year of the experiment, except year 3. Yields were highest in the 35-day cutting frequency in years 1 and 2. In the fourth year of the experiment the mean total yield of Pioneer Brand 545 and Condura 73 Brand was 29% higher (P&lt;0.05) than CUF 101. By the fourth year substantial amounts of grass were present in the 25- and 28-day cutting interval plots. The contrasts between dormant and active cultivars for the dry matter yield of each of the individual harvests were not consistent in the first two years. In the third and fourth years the active initially outyielded the dormant cultivars at all cutting intervals, but yields of both were generally similar at the end of the season. Increasing the interval between successive harvests generally decreased the mean leaf to stem ratio. The ratio of leaf to stem for CUF 101 was significantly lower (P&lt;0.05) than that for Pioneer Brand 545, with Condura 73 Brand tending to be intermediate. Within cutting intervals, mean declines in plant persistence were similar for cultivars from the different dormancy groups. Largest changes in plant frequency occurred in the fourth year when the mean frequency for the 25- and 28-day plots decreased from 69 to 12% compared with a mean decline from 74 to 65% for the 42- and 48-day cutting intervals. Productive stand life in this experiment was 3 years, even though disease was negligible. Under these conditions grass invasion was mainly related to harvest interval and much less to cultivar dormancy.

Effects of bath-applied GABA on the firing pattern of cells in an [formula omitted] preparation of mammalian cerebral cortex

The patterns of spontaneous firing recorded from 25 cells in slice preparations of rat cerebral cortex were characterised using inter-spike interval plots (ISI). Histograms of the ISI showed two peaks having modal values of 20 and 88ms, corresponding to episodes of high frequency bursts of action potentials, and a lower frequency, steady pattern of activity. Bath-applied GABA was shown to reversibly block the bursting activity, but had little effect on the lower frequency component. This effect of GABA could be abolished by the simultaneous application of bicuculline.

A neuroelectric signal recognition system

A neuroelectric signal recognition program written for a DEC PDP-12 digital computer is described. Unit selections are made on the basis of the minimal mean square amplitude differences between the incoming displayed signal and previous “template unit” selections. These templates are continuously being replaced by the incoming “units of best fit”, thus ensuring an automatic compensation for slow shape trends. Interference patterns caused by simultaneously firing units are automatically stored for special analysis. This is a semi-automatic procedure carried out immediately after the fully automatic phase and ensures the correct sorting of interference potentials. When all units have been accounted for, the following histograms can be displayed for each unit type: a simple interval versus time plot; an interval occurrence probability histogram; a joint interval histogram.