Variability of spike trains and the processing of temporal patterns of acoustic signals—problems,constraints, and solutions

Object recognition and classification by sensory pathways is rooted in spike trains provided by sensory neurons. Nervous systems had to evolve mechanisms to extract information about relevant object properties, and to separate these from spurious features. In this review, problems caused by spike train variability and counterstrategies are exemplified for the processing of acoustic signals in orthopteran insects. Due to size limitations of their nervous system we expect to find solutions that are stripped to the computational basics. A key feature of auditory systems is temporal resolution, which is likely limited by spike train variability. Basic strategies to reduce such variability are to integrate over time, or to average across several neurons. The first strategy is constrained by its possible interference with temporal resolution. Grasshoppers do not seem to explore temporal integration much, in spite of the repetitive structure of their songs, which invites for multiple looks at the signal. The benefits of averaging across neurons depend on uncorrelated responses, a factor that may be crucial for the performance and evolution of small nervous systems. In spite of spike train variability the temporal information necessary for the recognition of conspecifics is preserved to a remarkable degree in the auditory pathway.Abbreviations dB decibel - CV coefficient of variation - SNR signal to noise ratio     

Assessment of temporal resolution of multi-detector row computed tomography in helical acquisition mode using the impulse method

The purpose of this study was to propose a method for assessing the temporal resolution (TR) of multi-detector row computed tomography (CT) (MDCT) in the helical acquisition mode using temporal impulse signals generated by a metal ball passing through the acquisition plane. An 11-mm diameter metal ball was shot along the central axis at approximately 5 m/s during a helical acquisition, and the temporal sensitivity profile (TSP) was measured from the streak image intensities in the reconstructed helical CT images. To assess the validity, we compared the measured and theoretical TSPs for the 4-channel modes of two MDCT systems. A 64-channel MDCT system was used to compare TSPs and image quality of a motion phantom for the pitch factors P of 0.6, 0.8, 1.0 and 1.2 with a rotation time R of 0.5 s, and for two R/P combinations of 0.5/1.2 and 0.33/0.8. Moreover, the temporal transfer functions (TFs) were calculated from the obtained TSPs. The measured and theoretical TSPs showed perfect agreement. The TSP narrowed with an increase in the pitch factor. The image sharpness of the 0.33/0.8 combination was inferior to that of the 0.5/1.2 combination, despite their almost identical full width at tenth maximum values. The temporal TFs quantitatively confirmed these differences. The TSP results demonstrated that the TR in the helical acquisition mode significantly depended on the pitch factor as well as the rotation time, and the pitch factor and reconstruction algorithm affected the TSP shape.     

Rats’ (Rattus norvegicus) temporal discrimination of brief auditory stimuli: How does it compare with that of humans (Homo sapiens) and zebra finches (Taeniopygia guttata)?

The present study with rats replicated an experiment on the ability of zebra finches and humans to discriminate among brief auditory stimuli (see Weisman et al., 1999, Experiment 2). We trained rats with 27 3-kHz tones that varied in duration from 10 ms to 1420 ms. Reinforcement was contingent on responding (approaching the food well) to the nine medium-durations range tones (56-255 ms) but not to the nine short-durations range (10-46 ms) or long-durations range tones (309-1420 ms). Rats also received post-discrimination transfer tests with 2 kHz and 4 kHz tones that varied over the same durations as the 3 kHz tones. Rats acquired the temporal discrimination to a slightly lower level of accuracy than seen in finches or humans by Weisman et al. (1999). We tested for transfer of the temporal discrimination to find that rats, similar to humans (data from Weisman et al., 1999), transferred to untrained 2-kHz and 4-kHz tones at levels approaching accuracy to that achieved to the trained 3-kHz tone. By contrast, zebra finches (data from Weisman et al., 1999) failed to transfer their discrimination to the trained tone. We conclude that (a) rats discriminate among tone durations at least as well as they do among auditory frequencies and (b) rats like humans, but unlike finches, are insensitive to absolute pitch in their temporal discrimination.     

Developing indices of temporal dispersion and continuity to map natural vegetation

An accurate and updated natural vegetation map is imperative for sustainable environmental management. This paper proposed a novel natural vegetation mapping algorithm based on time series images. Several indices of temporal dispersion and continuity were established for this purpose: low density (LD), medium density (MD), high density (HD) and medium continuity (MC). These indices were developed based on the particular percentiles-determined section of the EVI2 temporal profiles obtained through continuous wavelet transform. The natural vegetation was generally characterized as with lower temporal dispersion and greater temporal continuity compared with agricultural crops. The proposed methodology incorporated the indices of temporal dispersion and continuity and was applied to 13 provinces in central East China based on 500 m 8-day composite Moderate Resolution Imaging Spectroradiometer (MODIS) Enhanced Vegetation Index with two bands (EVI2) in 2013. An overall accuracy of 92.97% was obtained when compared with 2715 ground truth sites. There was also a good agreement (kappa index = 0.8049) on the distribution and areas of different vegetation types between the MODIS-estimated image and the Landsat 8 OLI interpreted data on two test regions. This study demonstrated the efficiency of the transform and metric integrated time series classification approaches in the fields of land and vegetation cover mapping.     

Time perception and temporal processing levels of the brain

A classification is presented to structure divergent empirical findings on temporal mechanisms of the brain. Proceeding from our time experiences of simultaneity, nonsimultaneity, temporal order, duration, and the subjective present, a classification of thresholds is established that marks distinct processes involved in time perception and the temporal control of movements. On the basis of this classification, evidence has been collected that suggests that perception and action share common timing mechanisms. Furthermore, brain structures involved in temporal aspects of behavior on different time scales have been identified-namely, the cerebellum, the basal ganglia, and circumscribed cortical regions. Another question under debate concerns the representational mode in which time is represented in the brain; models suggest neuronal oscillations or interval-based mechanisms.     

Establishment success and extinction risk in autocorrelated environments

We consider establishment success (and extinction risk of small populations) in fluctuating environments, by means of an inhomogeneous branching process model. In this model it is assumed that individuals reproduce asexually during discrete reproduction periods. Within each period individuals reproduce independently and have random numbers of offspring. Expected numbers of offspring vary over reproduction periods due to random environmental changes. Previous simulation results indicated that there is a positive autocorrelation between the establishment probabilities of invaders in successive reproduction periods when environmental states are independently distributed. This result was never formally proved. In this paper we prove that this is indeed true, regardless of the form of the distribution of environmental states or the offspring distribution (under a monotonicity condition, which holds for biologically realistic models). Furthermore, we prove that it is also true for positively autocorrelated environmental states. We show by a counterexample that in environments with a strong negative autocorrelation establishment probabilities can be negatively autocorrelated. This was further examined through simulations. Our results imply that in independent, positively autocorrelated and weakly negatively autocorrelated environments the probability of success of invasion in different independently varying sites is the highest, followed by sequential invasion. For environments with a strong negative autocorrelation, sequential invasion has the highest probability of success. Effects of autocorrelation were further examined with simulations. From the results it appears that the expected length of 'runs of bad luck' is the most crucial factor for establishment success.     

不同首剂匹罗卡品制作颞叶癫痫大鼠模型的研究

目的:研究不同首次剂量匹罗卡品对氯化锂-匹罗卡品颞叶癫痫大鼠模型诱发成功率、死亡率的影响。方法:90只SD大鼠随机分为三组,每组首次使用匹罗卡品剂量:A组10mg/kg、B组20mg/kg、C组30mg/kg;随后采用多次注射10mg/kg匹罗卡品,比较3组癫痫持续状态诱发成功率、死亡率的差异。结果:A、B、C组癫痫持续状态诱发成功率分别为66.7%、90%、93.3%。其中A组与B组之间诱发成功率差异有统计学意义,P<0.05;C组与B组之间相比,差异无统计学意义,P>0.05。三组死亡率分别为20%、23.3%、57.1%,其中A组与B组之间差异无统计学差异,P>0.05,;C组与其它两组相比较差异有统计学差异,P<0.05。结论:首次剂量20mg匹罗卡品,然后10mg多次反复注射,癫痫持续状态诱发成功率高、死亡率低,是一种理想的颞叶癫痫模型。     

Temporal snychrony and patterns in an exotic host-parasitoid community

We studied an imported host-parasitoid community in Hawaii, asking to what extent the species covaried in a systematic fashion even though all species were exotic to Hawaii, and occurred in an artificial agroecosystem (a commercial guava, Psidium guajava L., orchard). Using knock-down pyrethrin sprays we were able to accurately quantify numbers of the host, [oriental fruit fly, Bactrocera dorsalis (Hendel)] and its four major parasitoid species [Biosteres arisanus (Sonan), Diachasmimorpha longicaudata (Ashmead), Psyttalia incisi (Silvestri), and Bi. vandenboschi (Fullaway)] at hourly intervals. We found that the parasitoids' activity and abundance was well correlated with the activity and abundance of their host, and that all four parasitoid species covaried in concert with one another. In fact, the magnitude of correlation between the different species in this system was greater than the correlation with temperature. This show clearly that an entirely exotic community, reassembled piecemeal as a result of biocontrol efforts, can end up with patterns of temporal covariation that are highly coincident. One other interesting result concerns the speed with which sprayed trees were recolonized by the fruit fly and its parasitoids. The time that it took each species to reach its mean density prior to removal by the first pyrethrin spray at 0600 hours varied. It took 2 h for female B. dorsalis to recolonize guava trees to pre-spray levels. It took 3 h for Bi. arisanus, 4 h for D. longicaudata, 7 h for Bi. vandenboschi and 14 h for P. incisi to reach pre-spray levels. The fact that Bi. arisanus recolonized vacant trees almost as rapidly as did the fruit fly pest suggest that there is little opportunity for the fruit fly to escape in space and time by staying one step ahead of its enemies.     

Dynamic membrane structure induces temporal pattern formation

The understanding of temporal pattern formation in biological systems is essential for insights into regulatory processes of cells. Concerning this problem, the present work introduces a model to explain the attachment/detachment cycle of MARCKS and PKC at the cell membrane, which is crucial for signal transduction processes. Our model is novel with regard to its driving mechanism: Structural changes within the membrane fuel an activator–inhibitor based global density oscillation of membrane related proteins. Based on simulated results of our model, phase diagrams were generated to illustrate the interplay of MARCKS and PKC. They predict the oscillatory behavior in the form of the number of peaks, the periodic time, and the damping constant depending on the amounts of MARCKS and PKC, respectively. The investigation of the phase space also revealed an unexpected intermediate state prior to the oscillations for high amounts of MARCKS in the system. The validation of the obtained results was carried out by stability analysis, which also accounts for further enhanced understanding of the studied system. It was shown, that the occurrence of the oscillating behavior is independent of the diffusion and the consumption of the reactants. The diffusion terms in the used reaction–diffusion equations only act as modulating terms and are not required for the oscillation. The hypothesis of our work suggests a new mechanism of temporal pattern formation in biological systems. This mechanism includes a classical activator–inhibitor system, but is based on the modifications of the membrane structure, rather than a reaction–diffusion system.     

Dynamics of temporal control in rats: the effects of a brief transition in interval duration

Five rats lever-pressed for liquid reinforcers delivered according to a fixed-interval (FI) reinforcement schedule, where the interval requirement changed at an unpredictable point within a session. In a short square wave (SSW) condition, eight 30-s intervals were intercalated in a series of 120-s intervals so that the intervals changed from 120 to 30 s then back to 120 s. In a long square wave (LSW) condition the intervals changed from 120 to 480 s then back to 120 s. We observed rapid temporal control of post-reinforcement wait time duration by the IFI duration in the SSW condition only: Wait times decreased significantly during a transition to shorter (30 s) intervals; whereas wait times did not reliably increase during a transition to longer (480 s) intervals. Furthermore, in the SSW condition, wait time in post-transition intervals was shorter than that observed during pre-transition intervals. The results show that rats' wait times are sensitive to moment-to-moment changes in interval duration and that the dynamics depend on the direction in which the intervals change.     

Processing of behaviorally relevant temporal parameters of acoustic stimuli by single neurons in the superior olivary nucleus of the leopard frog

Summary Response characteristics of 130 single neurons in the superior olivary nucleus of the northern leopard frog (Rana pipiens pipiens) were examined to determine their selectivity to various behaviorally relevant temporal parameters [rise-fall time, duration, and amplitude modulation (AM) rate of acoustic signals. Response functions were constructed with respect to each of these variables. Neurons with different temporal firing patterns such as tonic, phasic or phasic-burst firing patterns, participated in time domain analysis in specific manners. Phasic neurons manifested preferences for signals with short rise-fall times, thus possessing low-pass response functions with respect to this stimulus parameter; conversely, tonic and phasic-burst units were non-selective and possessed all-pass response functions. A distinction between temporal firing patterns was also observed for duration coding. Whereas phasic units showed no change in the mean spike count with a change in stimulus duration (i.e., all-pass duration response functions), tonic and phasic-burst units gave higher mean spike counts with an increase in stimulus duration (i.e., primary-like high-pass response functions). Phasic units manifested greater response selectivity for AM rate than did tonic or phasic-burst units, and many phasic units were tuned to a narrow range of modulation rates (i.e., band-pass). The results suggest that SON neurons play an important role in the processing of complex acoustic patterns; they perform extensive computations on AM rate as well as other temporal parameters of complex sounds. Moreover, the response selectivities for rise-fall time, duration, and AM rate could often be shown to contribute to the differential responses to complex synthetic and natural sounds.Abbreviations SON superior olivary nucleus - DMN dorsal medullary nucleus - TS torus semicircularis - FTC frequency threshold curve - BF best excitatory frequency - PAM pulsatile amplitude modulation - SAM sinusoidal amplitude modulation - SQAM square-wave amplitude modulation - MTF modulation transfer function - PSTH peri-stimulus time histogram     

On the squamosal suture of KNM-WT 17000.

The extensive overlap of the temporal squama on the parietal in KNM-WT 17000 is restricted to a narrow segment of the arc of the squamosal suture. It appears as a long, narrow, posterosuperior extension onto the calvarial wall. The long axis of this extended strip is aligned with what appears to be the most hypertrophied section of the temporalis muscle fan. The substantial differences between the squamosal suture and associated masticatory elements of KNM-WT 17000 and those of Australopithecus boisei provide an opportunity to evaluate the various forces molding the anatomy of the squamosal suture of A. boisei. It is suggested that the extreme flare of the zygomatic arches in the latter accounts for these differences.     

Trends in regional cancer mortality in Taiwan 1992–2014

BackgroundAlthough the cancer mortality rate in Taiwan has been declining in recent years, no study has yet reported any regional differences in cancer mortality rates in Taiwan. We hypothesized that regional cancer mortality rates in Taiwan, an ethnically homogeneous society, exhibited no significant variations.MethodsWe investigated the trends in Taiwan regional cancer mortality between 1992 and 2014. We analyzed regional age-standardized cancer mortality rates for lung, liver, colon, stomach, oral, breast, and prostate cancers using the Taiwan Longitudinal Health Insurance Database and Demographic Database. Furthermore, we applied Joinpoint regression analysis to evaluate the trends across different regions.ResultsThere are clear regional variations in mortality rates for liver, stomach, and oral cancers, but not for lung, colon, breast, and prostate cancers. The regional death rates of oral cancer, especially for eastern Taiwan, not only elevate the fastest (APC = 14.78% per year, P < 0.001) but also show the largest disparities between men and women. Regional death rates for stomach cancer, which declined most rapidly, are converging in both general and gender groups. Liver cancer is the only one with regional variations whose trends do not all go in the same direction. We also demonstrated that northern Taiwan has significant regional advantages with respect to cancer mortality.ConclusionsSome but not all cancers in Taiwan show regional disparities. Liver, stomach, and oral cancers in Taiwan exhibit clear regional variations in mortality rates. In particular, the regional variations in oral cancer mortality rates are consistent with those in alcohol consumption.     

Electrophysiological and psychophysical quantification of temporal summation in the human nociceptive system

Animal experiments have shown that the nociceptive reflex can be used as an indicator of central temporal integration in the nociceptive system. The aim of the present study on humans was to investigate whether the nociceptive reflex, evoked by repetitive strong electrical sural nerve stimuli, increased when summation was reported by the volunteers. The reflexes were recorded from the biceps femoris and rectus femoris muscles in eight volunteers following a series of stimulations at 0.1, 1, 2, and 3 Hz. Each series consisted of five consecutive stimuli. Using 0.1- and 1-Hz stimulation, the reflex was not facilitated in the course of the five consecutive stimuli. Following 2- and 3-Hz stimulation, the reflex size (root mean square amplitude) increased significantly during the course of the fifth stimulus. This reflex facilitation was followed by a significant increase (summation) in the pain magnitude when compared with 1- and 0.1-Hz stimulation. Furthermore, the threshold for psychophysical summation could be determined. This threshold (stimulus intensity) decreased when the stimulus frequency (1–5 Hz) of the five consecutive stimuli was increased. The nociceptive reflex and the psychophysical summation threshold might be used to clarify and quantify aspects of temporal summation within the human nociceptive system.     

Species temporal variability: epigaeic ant assemblages and management for abundance and scarcity

Summary Ant assemblages in five closely-spaced point habitats were studied over a three-year period in a subtropical area of South Africa. A total of 20,746 individuals in 56 species were sampled with pitfall traps. Rapid species turnover occurred during short periods after longer intervals of relatively constant species composition. There was annual cycling of total numbers of individuals. The temporal variance for total number of individuals within each habitat increased significantly with mean population size by a logarithmic regression. This indicates that population fluctuations are dependent upon the mean, with a distinctive relationship. The total number of species was cyclical, with annual and approximately half-yearly cycles. Each habitat nevertheless carried a characteristic mean number of species. The temporal variance of species richness showed a highly significant positive logarithmic relationship with the mean number of species. Pheidole megacephala (F.) accounted for 45% of all individuals. Its overall population showed annual cycles. Ph. megacephala population trend was the main determinant for seasonal variation of the whole assemblage in most habitats. Percentage dominance was positively linearly correlated with the variance and with mean population level. Although Ph. megacephala population variance increased with the mean, proportionate variability did not, indicating that high populations are no more variable than low populations. Five variability measures were compared with each other on ant assemblages containing only the common species (1st quartile) and then including the increasingly rare species (1st and 2nd, 1st, 2nd and 3rd, and all quartiles). Williamson's Variability Measure, using logarithmic or inverse sine transformations, gave variable results depending whether or not the rarer species were included in the analysis. The Coefficient of Fluctuation also gave variable results depending on assemblage size. The Coefficient of Variation and Proportionate Variability Measure gave similar and consistent results, indicating that common species are not more variable than rare ones. The rarer species are stenotopic and tend always to be rare, whereas the common species are eurytopic, highly competitive and demographically volatile. Control measures for common ants, and conservation of rare ants, should take cognizance of these trends.     

Density dependence of Anaphes sordidatus (Hymenoptera: Mymaridae) parasitism on eggs of Listronotus oregonensis (Coleoptera: Curculionidae)

Listronotus oregonensis (LeConte) (Coleoptera: Curculionidae) oviposits in carrot leaves and the larvae feed in carrot roots. Its eggs are parasitized by Anaphes sordidatus (Girault) (Hymenoptera: Mymaridae) throughout its oviposition period. This parasitoid is the major biotic mortality factor for L. oregonensis. Parasitism by A. sordidatus was studied for three years in sequentially sown plots of carrots, Daucus carota var. sativa. Over the scason, significantly fewer L. oregonensis eggs were oviposited in later sown carrots than in earlier sown carrots because oviposition started later in late sown plots of carrots. A positive temporal density-dependent relationship was observed each year between parasitism rates and host densities. This positive density dependence occurred in early and mid-summer for earlysown carrots where host density reached 1–2 host eggs per plant but disappeared in late summer when host density decreased while parasitism remained high. Latesown carrots had low host egg density (0.2 host egg per plant) and contributed little to the total number of eggs. In these late sown plots, parasitism increased rapidly to over 80% but no density dependence was observed. Spatially, few statistically significant regressions were found but all indicated a positive spatial density-dependence. Most non-significant regressions occurred because the range of egg density was too small between plots for a given date.     

Time estimation of fear cues in human observers

Previous research suggests that time judgments are a function of the affective properties of to-be-timed stimuli and that time judgments are longer for stimuli that are fear-inducing (e.g., [Hare, 1963] and [Watts and Sharrock, 1984]). The goals of the present study were twofold: to replicate the effect of a fear cue on time estimation, and to evaluate the mechanism underlying the effect. Seven stimulus durations in two different duration ranges (short: 250-1000 ms; long: 400-1600 ms) were employed in the bisection procedure. Adult human participants were exposed to two successive sessions, one each with the short and long range. Images from the International Affective Picture System (IAPS; Lang et al., 2008) that were rated on three scales including arousal and fear were presented as temporal stimuli. Three images that were rated high on fear and three rated low served as fear cues and neutral control images, respectively. Results indicated that for both ranges, judgments were longer for fear cues than for neutral images, and that the magnitude of the effect did not differ between ranges as measured by the bisection point. Application of scalar expectancy theory (SET; [Gibbon, 1977] and [Church, 1984]) to these results suggests that the fear effects were mediated by switch latency of an internal clock, rather than by clock speed.