Spiking Regularity Research Articles

Response properties and biological function of the skate electrosensory system during ontogeny.

This study examined the response properties of skate electrosensory primary afferent neurons of pre-hatch embryo (8-11 weeks), post-hatch juvenile (1-8 months), and adult (> 2 year) clearnose skates (Raja eglanteria) to determine whether encoding of electrosensory information changes with age, and if the electrosense is adapted to encode natural bioelectric stimuli across life history stages. During ontogeny, electrosensory primary afferents increase resting discharge rate, spike regularity, and sensitivity at best frequency. Best frequency was at 1-2 Hz for embryos, showed an upwards shift to 5 Hz in juveniles, and a downward shift to 2-3 HZ in adults. Encapsulated embryos exhibit ventilatory movements that are interrupted by a "freeze response" when presented with weak uniform fields at 0.5 and 1 Hz. This phasic electric stimulus contains spectral information found in potentials produced by natural fish predators, and therefore indicates that the embryo electrosense can efficiently mediate predator detection and avoidance. In contrast, reproductively active adult clearnose skates discharge their electric organs at rates near the peak frequency sensitivity of the adult electrosensory system, which; facilitates electric communication during social behavior. We suggest that life-history-dependent functions such as these may shape the evolution of the low-frequency response properties for the elasmobranch electrosensory system.

Birthweight between 14 and 42 weeks' gestation.

Data representing fetal weight gain between 14 and 42 weeks' gestation are presented; firstly to provide suitable curves enabling the growth of the very immature infant to be monitored and secondly to examine the influence of the improved techniques of paediatric and obstetric assessment developed since the publication of previous studies. Data have been collected from the 57 866 livebirths in Sheffield between 1976 and 1984 and from therapeutically terminated and spontaneously aborted fetuses over the same period. It seems that preterm livebirths do not form a different population with respect to weight from the fetus still in utero, at least until the beginning of the third trimester. Previous studies have reported a bimodality of weight distribution in preterm infants at each gestational age which has been attributed to errors in gestational assessment. The pattern of distribution of weight in this study suggests that early ultrasonography and paediatric assessment techniques have exerted a considerable influence on the accuracy of gestational assessment. The mean weights of the sample differ considerably from those of the Gairdner and Pearson chart which are, therefore, considered to be inappropriate for the Sheffield population.

Input-output analysis of an IPFM neural model: effects of spike regularity and record length.

This paper analyzes a model neural modulating system in which the input is a continuous sinusoid and the output is a point process modulated (integral pulse frequency modulation or IPFM) by the output of a linear system. Analytical expressions for the spectrum of the output point process are used to evaluate transfer function estimation procedures. The detectability of the spectral peak at the modulation frequency depends on the record length and upon the bias and variance contributed by the underlying point process. Detectability is found to increase with regularity of the underlying point process when stimulus frequency is much lower than spike rate, decreases with regularity when the stimulus frequency is about equal to spike rate, and be nearly independent of regularity at high frequencies. These results suggest certain procedures for evaluating the transfer function: 1) at low stimulus frequencies direct estimate of the spectrum is appropriate, 2) at middle frequencies, close to the spike rate, an estimate of the period point density may improve the detectabiity of the spectral peak, and 3) at middle frequencies, broad-band noise added to the sinusoidal stimulus may improve the estimate by decreasing the regularity of the underlying point process. Evaluation of the transfer function using broad-band rather than sinusoidal stimulus may have the advantage of decreasing bias and variance due to regularity of the underlying process, but may introduce a bias of unknown spectral character due to the response of the linear system itself and contribute a nonuniform spectral density at high frequencies.

UNDAMPED REGULAR SPIKING OF A RUBY LASER IN A MISALIGNED CAVITY

Regular spiking of a ruby laser has been observed in a cavity with two plane mirrors, one of which was tilted. With the introduction of a lens the regularity and reproducibility of the regular spiking was improved considerably.

INHERITANCE STUDIES OF SEVERAL QUALITATIVE AND QUANTITATIVE CHARACTERS IN SPRING WHEAT CROSSES BETWEEN VARIETIES RELATIVELY SUSCEPTIBLE AND RESISTANT TO DROUGHT

Genetic studies were made in the F2 and F3 generations of the crosses, Selection I-28-60 × Milturum, Reward × Caesium, and Caesium × Marquis. It was found that the character glume color was controlled by either one or two factor pairs in the cross Selection I-28-60 × Milturum, and by two factor pairs in the crosses Reward × Caesium and Caesium × Marquis. The characters, awning, straw color, glume pubescence and spike regularity were each governed by one factor pair, while three factor pairs were operative in the inheritance of seed color.Polymeric factors apparently control the inheritance of the quantitative characters straw strength, plant height, earliness and grain yield. A partial dominance of strong straw and earliness was found in the crosses Reward × Caesium and Caesium × Marquis. Tallness and low grain yield were partially dominant in the cross Reward × Caesium. Evidence for transgressive segregation of earliness was obtained in the cross between Caesium and Marquis.The characters glume color, awning, straw color, glume pubescence and spike regularity were inherited independently. White straw color and earliness were definitely associated in the crosses Reward × Caesium and Caesium × Marquis. The characters straw color and plant height were loosely linked in the Caesium × Marquis cross. Grain yield was not significantly correlated with straw strength, plant height or earliness in the cross between Reward and Caesium. Small but significant relationships were found among the characters straw strength, plant height and earliness in the crosses Reward × Caesium and Caesium × Marquis. The relation between heading and maturity was studied only in the F4 of Reward × Caesium, in which case a strong positive correlation was obtained.