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A general analysis of undistorted propagation of localized wave packets in photonic crystals based on a Wannier-function expansion technique is presented. Different kinds of propagating and stationary spatiotemporal localized waves are found from an asymptotic analysis of the Wannier function envelope equation.
Scaffold/matrix attachment regions (S/MARs) are essential for structural organization of the chromatin within the nucleus and serve as anchors of chromatin loop domains. A significant fraction of genes in Arabidopsis thaliana contains intragenic S/MAR elements and a significant correlation of S/MAR presence and overall expression strength has been demonstrated. In this study, we undertook a genome scale analysis of expression level and spatiotemporal expression differences in correlation with the presence or absence of genic S/MAR elements. We demonstrate that genes containing intragenic S/MARs are prone to pronounced spatiotemporal expression regulation. This characteristic is found to be even more pronounced for transcription factor genes. Our observations illustrate the importance of S/MARs in transcriptional regulation and the role of chromatin structural characteristics for gene regulation. Our findings open new perspectives for the understanding of tissue- and organ-specific regulation of gene expression.
Noise-induced transitions in the organization of systems far from equilibrium have been of vital interest. Although the effects of additive and multiplicative noise have been widely studied, it is only the multiplicative noise that can be dealt with within the scope of a linear analysis of first moments of the spatiotemporal perturbations, by the application of Novikov's theorem. For the case of additive noise, the corresponding straightforward linear analysis of the first moment throws no light on the effect of the noise on stability conditions. We propose here a simple approach based on higher-order moments to show how additive noise can give rise to noise-induced instability in spatially extended systems, at times leading to pattern formation. Our theoretical analysis is corroborated by numerical simulations on two simple one-component reaction-diffusion systems in two dimensions.
To determine the benefit of motor programming analysis for distinguishing patients with parkinsonism, we compared the spatiotemporal pattern of event-related desynchronization (ERD) preceding a self-paced voluntary wrist flexion between two groups of 10 patients with progressive supranuclear palsy (PSP) and Parkinson's disease (PD) and 10 control subjects. ERD of the mu rhythm was computed from 11 source derivations covering the medial frontocentral, central, and parietocentral areas during two successive left and right experimental conditions (80 self-paced wrist flexions). ERD began in the control group 1750 ms before movement onset over the contralateral central area and then appeared bilaterally on movement execution. In both patient groups, spatiotemporal distribution differed from that in the control group. In the PSP group, ERD had a shorter latency over the contralateral primary sensorimotor area compared with the PD group (PSP: 375 ms before movement onset for both conditions; PD: right flexion 1125 ms before movement onset, left flexion 1000 ms). ERD was observed over the parietocentral area in both groups but also with a clear reduction of latency before movement onset in the PSP group. In both groups, a bilateral central pattern appeared 250 ms before movement execution. In conclusion, our study indicates that ERD analysis is a useful method for observing the changes in cortical activation and for measuring motor programming impairment in parkinsonism, which was more affected in PSP than in PD.
The neural network structure of a guinea-pig's primary auditory cortex is estimated by applying pattern-time-series analysis to the auditory evoked responses. Spatiotemporal patterns in click-evoked responses, observed by optical recording with voltage-sensitive dye, are analyzed by time series analysis using a multivariable autoregressive (MAR) model. Oscillatory neural activities with a distribution of about 10 approximately 40 Hz in the click-induced evoked responses are found in the cortical response field. The cortical regions where the distributed neural oscillations are generated are identified by pattern-time-series analysis. In addition, two types of cortico-cortical connections, unilateral and bilateral connections between the cortical points, are speculated to be the causes of oscillatory neural activity transfer. It can be said that the so-called synchronized neural oscillation, in the sense of coherency or correlation between the two evoked responses at the oscillatory frequency, does not necessarily represent real cortico-cortical neural connections at the evoked response points.
Because environmental information is often suboptimal, visual perception must frequently rely on the brain's reconstruction of contours absent from retinal images. Illusory contour (IC) stimuli have been used to investigate these "filling-in" processes. Intracranial recordings and neuroimaging studies show IC sensitivity in lower-tier area V2, and to a lesser extent V1. Some interpret these data as evidence for feedforward processing of IC stimuli, beginning at lower-tier visual areas. On the basis of lesion, visual evoked potentials (VEP), and neuroimaging evidence, others contend that IC sensitivity is a later, higher-order process. Whether IC sensitivity seen in lower-tier areas indexes feedforward or feedback processing remains unresolved. In a series of experiments, we addressed the spatiotemporal dynamics of IC processing. Centrally presented IC stimuli resulted in early VEP modulation (88-100 msec) over lateral-occipital (LOC) scalp--the IC effect. The IC effect followed visual response onset by 40 msec. Scalp current density topographic mapping, source analysis, and functional magnetic resonance imaging results all localized the IC effect to bilateral LOC areas. We propose that IC sensitivity described in V2 and V1 may reflect predominantly feedback modulation from higher-tier LOC areas, where IC sensitivity first occurs. Two additional observations further support this proposal. The latency of the IC effect shifted dramatically later (approximately 120 msec) when stimuli were laterally presented, indicating that retinotopic position alters IC processing. Immediately preceding the IC effect, the VEP modulated with inducer eccentricity--the configuration effect. We interpret this to represent contributions from global stimulus parameters to scene analysis. In contrast to the IC effect, the topography of the configuration effect was restricted to central parieto-occipital scalp.
Hox genes are transcriptional regulators of metazoan body regionalization along the anteroposterior axis that act by specifying positional identity in differentiating cells. ceh-13, the labial orthologue in Caenorhabditis elegans, is expressed both during embryogenesis and post- embryonic development. Using GFP reporter analysis and immunocytochemistry, we discovered a spatiotemporal pattern of gene expression in the male tail during the L3 and L4 larval stages that is TGF-beta pathway-dependent. Analysis of reporter activity in transgenic animals identified a distinct promoter region driving male tail-specific ceh-13 expression. We also report the interspecies conservation of sequence motifs within this region and speculate that, in the course of evolutionary diversification, ceh-13 may have acquired new functionality while conserving its homeotic role.
The aim of this study was to assess the accuracy of cardiac functional values obtained from free-breathing real-time cine CMR with the temporal sensitivity encoding (TSENSE) technique by comparing them with values obtained from conventional cine CMR. For the real-time cine CMR, two protocols were employed, one with good temporal resolution and one with good spatial resolution. The functional values obtained from the high temporal resolution real-time cine CMR agreed and correlated well with those of cine CMR. On the other hand, statistically significant but clinically slight overestimation of ESV (p < .05) and underestimation of EF (p < .01) were observed with the other protocol. Real-time cine CMR with TSENSE can provide acceptable cardiac functional values.
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It is still a matter of debate whether neurons in the higher central nervous system of anurans become progressively more sharply tuned to sounds that have a behavioral importance or that such coding is performed by (small) groups of neurons. The approach we have taken to investigate this matter comprises simultaneous single-unit recording using two microelectrodes in the auditory midbrain of the grassfrog. The present study deals with 96 pairs of units responding to an ensemble of natural and synthetic mating calls in which carrier frequency and pulse-repetition rate were varied. This ensemble was presented without noise and also with background noise of increasing intensity. The spike trains were analysed for correlations between their firings. In 34 pairs (35%) a functional connection, mostly common input, was present. By selecting one of the units of a pair as a trigger it was investigated which window for a coincidence analysis would result in enhanced specificity for the unit pair. Such an analysis based on a logical AND operation could be a model for the action of a neuron on which both units under study would converge, and which would then show an enhanced specificity in their response to a stimulus ensemble. It was found that in 20 pairs (21%) the logical AND operation was more selective than each of the component neurons. The largest time window for which the selectivity was found was evenly distributed over the values 8 ms, 32 ms and 128 ms, in one case selectivity was found only for a window of 2 ms. There was neither preference for selective pairs to be found for recordings with one electrode (45 cases) or dual electrodes (51), nor for independent (62) versus functionally connected (34) pairs. In some cases selectivity resulted in a preference for one specific call, in other cases it resulted in a loss of responsiveness to the masking noise effectively resulting in an enhanced signal-to-noise ratio. The analysis stresses the importance of spatiotemporal patterns of nervous activity for the representation of sounds in the auditory midbrain of anurans.
We demonstrate that superfluorescent scattering of light can occur when laser light is incident on a collection of dielectric Rayleigh particles suspended in a viscous medium. Using a linear stability analysis, an expression for the spatiotemporal evolution of the scattered (probe) field is derived. An approximate condition for the progression of the interaction into the nonlinear regime is deduced and it is shown that, in the nonlinear regime, the scattered field intensity shows the characteristic quadratic dependence on particle density expected from a superfluorescent or superradiant process, once the effects of pump depletion are accounted for.
Recent findings of simultaneous and well coordinated head-neck movements during single as well as rhythmic jaw opening-closing tasks has led to the conclusion that 'functional jaw movements' are the result of activation of jaw as well as neck muscles, leading to simultaneous movements in the temporomandibular, atlanto-occipital and cervical spine joints. It can therefore be assumed that disease or injury to any of these joint systems would disturb natural jaw function. To test this hypothesis, amplitudes, temporal coordination, and spatiotemporal consistency of concomitant mandibular and head-neck movements during single maximal jaw opening-closing tasks were analysed in 25 individuals suffering from whiplash-associated disorders (WAD) using optoelectronic movement recording technique. In addition, the relative durations for which the head position was equal to, leading ahead of, or lagging behind the mandibular position during the entire jaw opening-closing cycle were determined. Compared with healthy individuals, the WAD group showed smaller amplitudes, and changed temporal coordination between mandibular and head-neck movements. No divergence from healthy individuals was found for the spatiotemporal consistency or for the analysis during the entire jaw opening-closing cycle. These findings in the WAD group of a 'faulty', but yet consistent, jaw-neck behavior may reflect a basic importance of linked control of the jaw and neck sensory-motor systems. In conclusion, the present results suggest that neck injury is associated with deranged control of mandibular and head-neck movements during jaw opening-closing tasks, and therefore might compromise natural jaw function.
A theory of human second-order motion perception is proposed and further applied to the discrimination of texture slant. The computational algorithms for deriving the direction of left-right motion from a sequence of images are equivalent to the algorithms for deriving the direction of slant (e.g. from top left to bottom right or top right to bottom left) in a single 2D image. There is a broad range of phenomena for which Fourier analysis of the image plus a few simple rules gives a good account of human perception. The problem with this first-order analysis is that there exists a broad class of 'microbalanced' stimuli in which the motion or slant is completely obvious to human subjects but is invisible to first-order analysis. Microbalanced stimuli require second-order analysis which consists of non-linear preprocessing (spatiotemporal filtering followed by rectification of the input signal) before standard motion or slant analysis. To determine whether the second-order rectification is half-wave or full-wave, we construct two special microbalanced stimulus types: 'half-wave stimuli' whose motion (or texture slant) is interpretable by a half-wave rectifying system but not by full-wave or a first-order (Fourier) analysis and 'full-wave stimuli' which are interpretable only after full-wave rectification. Such experiments show that second-order texture-slant perception utilizes both half-wave and full-wave processes, second-order motion-direction discrimination depends predominantly on full-wave rectification and second-order spatial interactions such as lateral contrast-contrast inhibition and second-order Mach bands are exclusively full-wave.
The usefulness of digitized echocardiographic borders in quantitative regional left ventricular function analysis has been limited by the wide reported range for normal wall motion with this technique. We postulated that random error in endocardial border positioning is a major cause of this limitation. To test this hypothesis, we traced the endocardial borders field by field from 17 complete echocardiographic cycles in six dogs. These cycles showed a great deal of random movement, with each endocardial point reversing its motion an average of 18.5 times per cardiac cycle. Spatiotemporal Fourier analysis of these sequences demonstrated that most of the valid information on endocardial motion was contained in the first four temporal harmonics and the first seven spatial harmonics and that beyond these points the Fourier transform has the spectral characteristics of noise. Reconstruction of these 17 cycles eliminating all Fourier components above the sixth temporal and eighth spatial harmonics reduced the mean number of endocardial reversals per cycle to 2.3 (p less than .00001). To derive the optimal temporal and spatial cutoffs, we compared reconstructions of each of the 17 cycles with three M mode echocardiograms obtained simultaneously with the cross-sectional images. Fourier cutoffs were varied between two and 20 harmonics and demonstrated that the optimal temporal cutoff was 5.5 harmonics and optimal spatial cutoff 6.9. With optimal filtering, the correlation between ventricular diameter derived from the M mode and from the cross-sectional images was r = .965, compared with .877 for the M mode vs unfiltered cross-sectional data (p less than .0001). We conclude that two-dimensional filtered Fourier reconstruction significantly improves the accuracy of traced echocardiographic borders. This technique should be useful in the postprocessing of endocardial borders extracted by automated edge detection schemes and should also be applicable to cardiac images derived from modalities other than echocardiography.
The analysis of experimental time series, obtained from single and polycrystals subjected to constant strain rate tests, reports an intriguing dynamical crossover from a low-dimensional chaotic state at medium strain rates to an infinite-dimensional power-law state of stress drops at high strain rates. We present the results of an extensive study of all aspects of the Portevin-Le Chatelier (PLC) effect within the context of a recent model that reproduces this crossover. We characterize the dynamics of this crossover by studying the distribution of the Lyapunov exponents as a function of the strain rate, with special attention to system size effects. The distribution of the exponents changes from a small set of positive exponents in the chaotic regime to a dense set of null exponents in the scaling regime. As the latter is similar to the result in a shell model for turbulence, we compare the results of our model with that of the shell model. Interestingly, the null exponents in our model themselves obey a power law. The study is complimented by visualizing the configuration of dislocations through the slow manifold analysis. This shows that while a large proportion of dislocations are in the pinned state in the chaotic regime, most of them are pushed to the threshold of unpinning in the scaling regime, thus providing insight into the mechanism of crossover. We also show that this model qualitatively reproduces the different types of deformation bands seen in experiments. At high strain rates, where propagating bands are seen, the model equations can be reduced to the Fisher-Kolmogorov equation for propagative fronts, which in turn shows that the velocity of the propagation of the bands varies linearly with the strain rate and inversely with the dislocation density. These results are consistent with the known experimental results. We also discuss the connection between the nature of band types and the dynamics in the respective regimes. The analysis demonstrates that this simple dynamical model captures the complex spatiotemporal features of the PLC effect.
We studied spatiotemporal interactions in cat cortical receptive fields by presenting a stimulus composed of 16 narrow bars whose luminances were randomly modulated. Conventional stimuli were also presented to classify receptive field properties. A white noise estimate of the cell's response to a stepwise moving bar stimulus was calculated from responses to the spatiotemporal random stimulus. The white noise estimate captured the most important feature of the receptive field demonstrated by conventional stimuli, i.e. directional selectivity. In addition, the white noise analysis; (1) made visible inhibitory response phases that are usually below threshold; (2) subdivided the response into its linear and non-linear estimates; (3) further subdivided the non-linear estimate into spatial and temporal interactions; and (4) allowed estimation of responses to stimuli that were never explicitly presented.
We have isolated the cDNAs encoding the GnRH1 and GnRH2 precursors, respectively, from bullfrog (Rana catesbeiana) brain. The first cDNA consists of 648 bp and contains an open-reading frame of 270 nucleotides, encoding the bullfrog GnRH1 precursor. The second cDNA consists of 1053 bp and contains an open-reading frame of 255 nucleotides, encoding the bullfrog GnRH2 precursor. Both types of bullfrog GnRH precursor have a similar molecular architecture as observed in other GnRH precursors, consisting of a signal peptide, followed by the GnRH decapeptide, a conserved carboxy-terminal amidation and proteolytical processing site, and a GnRH-associated peptide (GAP). In addition, we have identified a third cDNA, containing 24 additional nucleotides in its GAP-coding region. Genomic PCR and sequence analysis confirmed that this cDNA represents an alternative splice variant of the bullfrog GnRH2-precursor pre-mRNA. The bullfrog GnRH1 precursor exhibits 60% and less than 40% amino acid identity to its Xenopus and mammalian counterparts, respectively, whereas the bullfrog GnRH2 precursor displays 50% to 60% amino acid identity to that of its nonmammalian counterparts, but shares only 25% amino acid identity with its mammalian counterparts. Northern blot analysis revealed a single GnRH1-precursor mRNA species of approximately 0.75 kilobases, expressed in bullfrog forebrain, and a single GnRH2-precursor mRNA species of approximately 1.1 kilobases, expressed in bullfrog midbrain/hindbrain. Furthermore, both bullfrog GnRH-precursor mRNAs exhibited a differential spatiotemporal expression pattern. Genomic Southern blot analysis indicated that both bullfrog GnRH genes are present as single copy genes. This is the first report on the molecular cloning of a GnRH2-precursor cDNA from an amphibian species. In addition, we present data showing that alternative splicing is utilized to generate different GnRH2-precursor mRNAs. J. Exp. Zool. 289:190-201, 2001.
Electrical alternans are believed to be linked to the onset of life-threatening ventricular arrhythmias and sudden cardiac death. Recent studies have shown that alternans can be suppressed temporally by dynamic feedback control of the pacing interval. Here we investigate theoretically whether control can suppress alternans both temporally and spatially in homogeneous tissue paced at a single site. We first carry out ionic model simulations in a one-dimensional cable geometry which show that control is only effective up to a maximum cable length that decreases sharply away from the alternans bifurcation point. We then explain this finding by a linear stability analysis of an amplitude equation that describes the spatiotemporal evolution of alternans. This analysis reveals that control failure above a critical cable length is caused by the formation of standing wave patterns of alternans that are eigenfunctions of a forced Helmholtz equation, and therefore remarkably analogous to sound harmonics in an open pipe. We discuss the implications of these results for using control to suppress alternans in the human ventricles as well as to probe fundamental aspects of alternans morphogenesis. (c) 2002 American Institute of Physics.