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PubMed1999

Automatic extraction and tracking of the tongue contours.

Computerized analysis of the tongue surface movement can provide valuable information to speech and swallowing research. Ultrasound technology is currently the most attractive modality for the tongue imaging mainly because of its high video frame rate. However, problems with ultrasound imaging, such as noise and echo artifacts, refractions, and unrelated reflections pose significant challenges for computer analysis of the tongue images and hence specific methods must be developed. This paper presents a system that is developed for automatic extraction and tracking of the tongue surface movements from ultrasound image sequences. The ultrasound images are supplied by the head and transducer support system (HATS), which was developed in order to fix the head and support the transducer under the chin in a known position without disturbing speech. In this work, we propose a novel scheme for the analysis of the tongue images using deformable contours. We incorporate novel mechanisms to 1) impose speech related constraints on the deformations; 2) perform spatiotemporal smoothing using a contour postprocessing stage; 3) utilize optical flow techniques to speed up the search process; and 4) propagate user supplied information to the analysis of all image frames. We tested the system's performance qualitatively and quantitatively in consultation with speech scientists. Our system produced contours that are within the range of manual measurement variations. The results of our system are extremely encouraging and the system can be used in practical speech and swallowing research in the field of otolaryngology.

Artifacts↗
PubMed1997

Evidence for synchronised responses in the piriform cortex by using Gibbs potential analysis.

The piriform cortex is a large paleocortical area which receives direct projections from the olfactory bulb. In order to study the spatiotemporal distribution of the piriform cortex activity, we chose optical recording of the responses evoked by olfactory bulb electrical stimulation. Such a stimulation elicited a large signal corresponding to cortical reactivation (disynaptic activity) via intrinsic association fibres. As the disynaptic activity was observed over the entire piriform area, we wondered whether or not this redistribution contributes to a synchronisation of the activity in the piriform cortex. In order to answer this question, we developed a statistical approach which allows us to take the temporal dimension into account. The analysis was performed by using the Gibbs potential analysis. The neural response of the diode is represented by a stochastic point process (occurrence of latency peak), and the response of the diode array is given as successive realisations of a binary random field defined on a finite set. The Gibbs measure associated with this field is then estimated through the interaction potentials of the field's configurations, which provide a quantitative evaluation of the interaction and the synchronisation between the neural sites. The analysis was performed on the latency of the peak of disynaptic activity, which was determined from signals from 60 different acquisitions realised with the same stimulus parameters. From these 60 files of latency values, we estimated the Gibbs interaction potential of singletons and pairs. The former gave an image of the spatiotemporal distribution of the disynaptic activity, which appears to propagate from the anterior to the posterior part of the area recorded. The estimation of the interaction potential of pairs allows us to characterise the degree of synchronisation between two neighbouring recording sites. It appeared that, in the anterior half of the area recorded, the disynaptic activity was statistically desynchronised whereas, in the posterior part the disynaptic activity appeared strongly synchronised. The functional implications of such a spatiotemporal distribution of the activity are discussed.

Models, Biological↗
PubMed2003

Neuroprotection assessment by topographic electroencephalographic analysis: effects of a sodium channel blocker to reduce polymorphic delta activity following ischaemic brain injury in rats.

The spatiotemporal electroencephalogram (EEG) pathology associated with brain injury was studied using high-resolution, 10-electrode cortical EEG mapping in a rat model of middle cerebral artery occlusion (MCAo). Using this model we evaluated the ability of the novel sodium channel blocker and neuroprotective agent RS100642 to resolve injury-induced EEG abnormalities as a measure of neurophysiological recovery from brain injury. The middle cerebral artery (MCA) was occluded for 1 h during which a dramatic loss of EEG power was measured over the injured cortex with near complete recovery upon reperfusion of blood to the MCA region in all rats. The resultant progression of the MCAo/reperfusion injury (6-72 h) included the appearance of diffuse polymorphic delta activity (PDA), as visually indicated by the presence of high-amplitude slow-waves recorded from both brain hemispheres. PDA was associated with large increases in EEG power, particularly evident in outer 'peri-infarct' regions of the ipsilateral parietal cortex as visualized using topographic EEG mapping. Post-injury treatment with RS100642 (1.0 mg/kg, i.v.) significantly reduced the PDA activity and attenuated the increase in EEG power throughout the course of the injury. These effects were associated with a reduction in brain infarct volume and improved neurological function. These methods of EEG analysis may be helpful tools to evaluate the physiological recovery of the brain from injury in humans following treatment with an experimental neuroprotective compound.

Animals↗
PubMed1998

Blind source separation and deconvolution: the dynamic component analysis algorithm.

We derive a novel family of unsupervised learning algorithms for blind separation of mixed and convolved sources. Our approach is based on formulating the separation problem as a learning task of a spatiotemporal generative model, whose parameters are adapted iteratively to minimize suitable error functions, thus ensuring stability of the algorithms. The resulting learning rules achieve separation by exploiting high-order spatiotemporal statistics of the mixture data. Different rules are obtained by learning generative models in the frequency and time domains, whereas a hybrid frequency-time model leads to the best performance. These algorithms generalize independent component analysis to the case of convolutive mixtures and exhibit superior performance on instantaneous mixtures. An extension of the relative-gradient concept to the spatiotemporal case leads to fast and efficient learning rules with equivariant properties. Our approach can incorporate information about the mixing situation when available, resulting in a "semiblind" separation method. The spatiotemporal redundancy reduction performed by our algorithms is shown to be equivalent to information-rate maximization through a simple network. We illustrate the performance of these algorithms by successfully separating instantaneous and convolutive mixtures of speech and noise signals.

Algorithms↗
PubMed2003

Characterization of onset mechanism and waveform analysis in patients with atrial fibrillation using a high-resolution noncontact mapping system.

INTRODUCTION: Information on the spatiotemporal organization of atrial activity at the onset of atrial fibrillation (AF) is limited. METHODS AND RESULTS: The study consisted of 26 consecutive patients (22 men and 4 women; mean age 56 +/- 9 years) with AF in whom the left atrium (LA) was mapped using a noncontact mapping system. At the onset of AF, the AF cycle lengths and wavefronts were analyzed at the site of origin of the triggering atrial premature complex (APC) and five predefined sites within the LA (superior, anterior, posterior, lateral, and septal walls). If repetitive activity was observed at the site of origin of APCs, triggered AF episodes were considered as focally driven. APCs that induced AF had shorter coupling intervals than APCs that did not induce AF (300 +/- 41 msec vs 392 +/- 64 msec, P < 0.001). Immediately after AF onset, repetitive firing was crucial for maintenance of arrhythmia in 52 (80%) of 65 AF episodes. In 13 AF onset episodes (20%), AF was maintained by other mechanisms. The number of LA wavefronts after AF onset was lower in focally driven AF episodes compared with episodes in which no focally driven activity was observed (1.9 +/- 0.6 v. 2.3 +/- 2.3 wavefronts, P < 0.05). After the onset of AF, the posterior wall of the LA showed the earliest disorganized activity (after 5.2 +/- 3.1 cycles). CONCLUSION: In the majority of AF episodes (80%), repetitive firing from the triggering foci may play an important role in maintaining AF immediately after arrhythmia onset. In 20% of the episodes, AF at early stages seems to be maintained by other mechanisms. The capability of APCs to induce AF depends on the coupling interval and the focus localization. The posterior wall of the LA shows the earliest disorganization of wavefronts at the onset of AF.

Adult↗
PubMed2004

Spatiotemporal tuning of optic flow inputs to the vestibulocerebellum in pigeons: differences between mossy and climbing fiber pathways.

The pretectum, accessory optic system (AOS), and vestibulocerebellum (VbC) have been implicated in the analysis of optic flow and generation of the optokinetic response. Recently, using drifting sine-wave gratings as stimuli, it has been shown that pretectal and AOS neurons exhibit spatiotemporal tuning. In this respect, there are two groups: fast neurons, which prefer low spatial frequency (SF) and high temporal frequency (TF) gratings, and slow neurons, which prefer high SF-low TF gratings. In pigeons, there are two pathways from the pretectum and AOS to the VbC: a climbing fiber (CF) pathway to Purkinje cells (P cells) via the inferior olive and a direct mossy fiber (MF) pathway to the granular layer (GL). In the present study, we assessed spatiotemporal tuning in the VbC of ketamine-anesthetized pigeons using standard extracellular techniques. Recordings were made from 17 optic-flow-sensitive units in the GL, presumably granule cells or MF rosettes, and the complex spike activity (CSA) of 39 P-cells, which reflects CF input. Based on spatiotemporal tuning to gratings moving in the preferred direction, eight GL units were classified as fast units, with a primary response to low SF-high TF gratings (mean = 0.13 cpd/8.24 Hz), whereas nine were slow units preferring high SF-low TF gratings (mean = 0.68 cpd/0.30 Hz). CSA was almost exclusively tuned to slow gratings (mean = 0.67 cpd/0.35 Hz). We conclude that MF input to the VbC is from both fast and slow cells in the AOS and pretectum, whereas the CF input is primarily tuned to slow gratings.

Action Potentials↗
PubMed2006

Study-level wavelet cluster analysis and data-driven signal models in pharmacological MRI.

In pharmacological MRI (phMRI) studies tracking signal changes following the acute administration of a compound, the spatiotemporal pattern of response is often unknown a priori. Moreover, when analysed within a general linear model (GLM) framework, the experimental paradigm of a single injection point under-informs the construction of an appropriate signal model, and information from pharmacokinetics or ancillary in vivo studies may be unavailable or insufficient to accurately describe the dynamic signal changes observed following injection of the drug. Here, we extend the application of a data-driven clustering algorithm, wavelet cluster analysis (WCA), to phMRI data from one or more groups of subjects in a study. A WCA decomposition of spatially concatenated time series' provides a compact overview of spatiotemporal response patterns across cohorts, highlighting typical temporal signatures, brain regions implicated in the response and inter-subject variability. Further, we demonstrate the use of regressors based on selected temporal components as suitable signal models in GLM-based analyses, resulting in a close fit to dynamic phMRI signal changes. This approach is illustrated with simulated data and two representative in vivo phMRI studies in the rat (nicotine and apomorphine challenges).

Animals↗
PubMed2000

Asynchronous updating of coupled maps leads to synchronization.

We investigate the spatiotemporal dynamics of two dimensional coupled map lattices, in the strong coupling phase, evolving under updating rules incorporating varying degrees of asynchronicity. Interestingly, we observe that parallel updates never allow synchronization among the sites, while asynchroncity has the effect of opening up windows in parameter space where the synchronized dynamics gains stability. As asynchronicity increases, the parameter range supporting synchronization gets rapidly wider. Detailed numerics, including bifurcation diagrams and patterns formed en route to synchronization, are reported. We also attempt a mean-field analysis of the system in order to try and account for the stability of the spatiotemporal fixed point under asynchronous updates. (c) 2000 American Institute of Physics.

Journal Article↗
PubMed2005

Oscillations in dc driven barrier discharges: numerical solutions, stability analysis, and phase diagram.

A short gas-discharge layer sandwiched with a semiconductor layer between planar electrodes shows a variety of spatiotemporal patterns. We focus on the spontaneous temporal oscillations that occur while a dc voltage is applied and while the system stays spatially homogeneous; the results for these oscillations apply equally to a planar discharge in series with any resistor with capacitance. We define the minimal model, identify its independent dimensionless parameters, and then present the results of the full time-dependent numerical solutions of the model as well as of a linear stability analysis of the stationary state. Full numerical solutions and the results of the stability analysis agree very well. The stability analysis is then used for calculating bifurcation diagrams. We find semiquantitative agreement with experiment for the diagram of bifurcations from stationary to oscillating solutions as well as for amplitude and frequency of the developing limit cycle oscillations.

Journal Article↗
PubMed2001

Geometrical analysis of chaotic mixing in a low Reynolds number magnetohydrodynamic quadripolar flow.

A mixing device for highly viscous fluids with finite electrical conductivity is investigated theoretically. Stirring is performed by means of electromagnetic forces provided by inductor wires located outside the flow domain. The flow shows hyperbolic and elliptic singular points. Inductors are displaced in a periodic manner, leading to an efficient stretching and folding mechanism. The goodness of mixing is quantified by means of a geometrical analysis based on box-counting techniques. This analysis gives valuable information about advection of a spot of dye injected in the flow, in the limit of infinite Peclet numbers. A spatiotemporal criterion for mixing efficiency is derived, and characteristic scales are analyzed. The influence of various parameters on mixing efficiency is discussed by making use of both the geometrical analysis and Poincaré sections.

Journal Article↗
PubMed2001

Site- and time-specific gene targeting in the mouse.

The efficient introduction of somatic mutations in a given gene, at a given time, in a specific cell type, will facilitate studies of gene function and the generation of animal models for human diseases. We have established a conditional site-specific recombination system in mice using a new version of the Cre/lox system. The Cre recombinase has been fused to a mutated ligand binding domain of the human estrogen receptor (ER), resulting in a tamoxifen-dependent Cre recombinase, Cre-ER(T), that is activated by tamoxifen, but not by estradiol. Transgenic mice were generated expressing Cre-ER(T) under the control of a cytomegalovirus promoter. Administration of tamoxifen to these transgenic mice induced excision of a chromosomally integrated gene flanked by loxP sites in a number of tissues, whereas no excision could be detected in untreated animals. However, the efficiency of excision varied between tissues, and the highest level (approximately 40%) was obtained in the skin. To determine the efficiency of excision mediated by Cre-ER(T) in a given cell type, Cre-ER(T)-expressing mice were crossed with reporter mice in which expression of Escherichia coli beta-galactosidase can be induced through Cre-mediated recombination. The efficiency and kinetics of this recombination were analyzed at the cellular level in the epidermis of 6- to 8-week-old double transgenic mice. Site-specific excision occurred within a few days of tamoxifen treatment in essentially all epidermis cells expressing Cre-ER(T). These results indicate that cell-specific expression of Cre-ER(T) in transgenic mice can be used for efficient tamoxifen-dependent Cre-mediated recombination at loci containing loxP sites, to generate site-specific somatic mutations in a spatiotemporally controlled manner. This conditional site-specific recombination system should allow the analysis of knockout phenotypes that cannot be addressed by conventional gene targeting.

Alleles↗
PubMed2006

Gene expression study in the juvenile mouse testis: identification of stage-specific molecular pathways during spermatogenesis.

A gene expression time course in the juvenile mouse testis was established using cDNA microarrays derived from a variety of isolated testis cell types. In conjunction with the use of four germ cell-deficient mouse models, a stage and cell-type classification over nine time points has been obtained and analyzed for differential expression of genes. The expression profiles have been clustered into nine groups and subjected to detailed analysis of associated gene ontology. This has allowed the correlation of particular cellular processes and functions with different expression clusters. Focused analysis of transcripts involved in cell number regulation (apoptosis and proliferation) and their spatiotemporal expression patterns are presented. The findings indicate that for genes involved in both apoptosis and proliferation, several distinct pathways regulating these processes are active in somatic and germ cell lineages.

Animals↗
PubMed1995

Carbamylcholine- and catecholamine-induced intracellular calcium dynamics of epithelial cells in mouse ileal crypts.

BACKGROUND/AIMS: The intestinal epithelium is composed of various cells, and the enteric nervous system, which controls the epithelial functions, has different neurotransmitters and/or modulators. The aim of this study was to show whether the responses of intestinal epithelial cells to different neurotransmitters are elicited throughout the entire epithelium or are restricted to a certain cell. METHODS: The spatiotemporal dynamics of cytosolic calcium ion ([Ca2+]c) were measured by digital imaging analysis in isolated crypts of mouse ileum loaded with [1-[2-(5'-carboxyoxazol-2'-yl)-6-amino-benzofuran-5- oxy]-2-(2'-amino-5'-methylphenoxy)-ethane-N,N,N',N'-tetraacetic acid] pentakis (acetoxylmethyl) ester. Thereafter, the crypt cells were identified morphologically. RESULTS: Carbamylcholine elicited [Ca2+]c dynamics in Paneth cells, showing a biphasic increase, but neither cholecystokinin octapeptide nor nicotine had any effect on the [Ca2+]c of the crypt cells including the Paneth cells. Adrenaline and noradrenaline, but not isoproterenol, induced a transient elevation of [Ca2+]c of some enterochromaffin cells. Increases in the [Ca2+]c of most crypt cells were elicited by thapsigargin. Propagation of a [Ca2+]c wave in the crypts was not evident. CONCLUSIONS: Increases in [Ca2+]c can be induced by carbamylcholine in Paneth cells and catecholamines in some enterochromaffin cells. The digital imaging analysis showed the heterogeneity of the responses of intestinal crypt cells to different transmitters.

Animals↗
PubMed2005

No effect of spatial phase randomisation on direction discrimination in dense random element patterns.

Two computational strategies have been proposed for motion analysis in the human visual system. Energy-based schemes involve detection of spatiotemporal Fourier energy in the frequency components comprising a moving pattern. Edge-based schemes track shifts in the position of local edges in the pattern over time. This paper describes a stimulus manipulation, spatial phase randomisation, that acts as a diagnostic test for the involvement of energy-based processes, and describes the results of two experiments which apply the manipulation to random element patterns. Both experiments compared direction discrimination performance in patterns before and after the spatial phase of their components was randomised in the Fourier domain. For dense patterns, there was no effect of phase randomisation on the maximum displacement supporting reliable direction discrimination, indicating that energy-based responses were dominant. For sparse patterns, a significant effect of phase randomisation was obtained, indicating a greater role for edge-based responses.

Discrimination, Psychological↗
PubMed1997

Miz1, a novel zinc finger transcription factor that interacts with Msx2 and enhances its affinity for DNA.

Msx2 is a homeobox gene with a regulatory role in inductive tissue interactions, including those that pattern the skull. We demonstrated previously that individuals affected with an autosomal dominant disorder of skull morphogenesis (craniosynostosis, Boston type) bear a mutated form of Msx2 in which a histidine is substituted for a highly conserved proline in position 7 of the N-terminal arm of the homeodomain (p148h). The mutation behaves as a dominant positive in transgenic mice. The location of the mutation in the N-terminal arm of the homeodomain, a region which in other homeodomain proteins plays a key part in protein-protein interactions, prompted us to undertake a yeast two hybrid screen for Msx2-interacting proteins. Here we present a functional analysis of one such protein, designated Miz1 (Msx-interacting-zinc finger). Miz1 is a zinc finger-containing protein whose amino acid sequence closely resembles that of the yeast protein, Nfi-1. Together these proteins define a new, highly conserved protein family. Analysis of Miz1 expression by Northern blot and in situ hybridization revealed a spatiotemporal pattern that overlaps that of Msx2. Further, Miz1 is a sequence specific DNA binding protein, and it can function as a positive-acting transcription factor. Miz1 interacts directly with Msx2 in vitro and enhances the DNA binding affinity of Msx2 for a functionally important element in the rat osteocalcin promoter. The p148h mutation in Msx2 augments the Miz1 effect on Msx2 DNA binding, suggesting a reason why this mutation behaves in vivo as a dominant positive, and providing a potential explanation of the craniosynostosis phenotype.

Amino Acid Sequence↗
PubMed2001

Quantitative electroencephalography spectral analysis and topographic mapping in a rat model of middle cerebral artery occlusion.

Electroencephalography (EEG) has a long history in clinical evaluations of cerebrovascular disease. Distinct EEG abnormalities, such as increased slow delta activity, voltage depression and epileptiform discharge, have been identified in stroke patients. However, preclinical use of EEG analysis of cerebral ischaemia is less documented. We report a new rat model of EEG topographic mapping during permanent and transient middle cerebral artery occlusion. Ten EEG electrodes were implanted on the rat skull, symmetrically covering the cortical regions of two hemispheres. Monopolar EEG recordings were acquired from each animal at multiple time points during the initial 24 h, and again once daily for 7 days. Traditional EEG examinations, quantitative EEG (qEEG) spectral analysis and topographic EEG mapping were employed for comprehensive data analyses. Several distinct spatiotemporal EEG abnormalities were identified in the ischaemic rat brain. In the ipsilateral hemisphere, pronounced increase in delta activity was observed in each recorded area within 24 h of injury. While sharp waves and spike complexes dominated the parietal region, a nearly isoelectric EEG state was seen in the temporal region. After 48 h, spontaneous, albeit incomplete, recovery of EEG activities developed in all rats. Reperfusion appeared to promote delta and alpha recovery more efficiently. The contralateral EEG changes were also recorded in two phases: an acute moderate increase in delta activities with intermittent rhythmic activities, followed by a delayed and significant increase in beta activities across the hemisphere. The similarities of rat qEEG profiles identified in this study to that of stroke patients and the application of topographic mapping broaden our research technology for preclinical experimental studies of brain injury.

Animals↗
PubMed2006

Evidence for indirect nosocomial transmission of Neisseria meningitidis resulting in two cases of invasive meningococcal disease.

Nosocomial transmission of Neisseria meningitidis has only rarely been reported. Here, we present a significant spatiotemporal association of two cases of invasive meningococcal disease identified by retrospective cluster analysis with the program SaTScan. The most likely epidemiological link was simultaneous hospitalization, resulting in indirect nosocomial transmission.

Adolescent↗
PubMed2004

Left atrial dilatation resulting from chronic mitral regurgitation decreases spatiotemporal organization of atrial fibrillation in left atrium.

Atrial conduction properties have been shown to differ among animal atrial fibrillation (AF) models of rapid atrial pacing (RAP), chronic mitral regurgitation (MR), and control. We hypothesized that these conduction differences would continue with the onset of AF, which would affect AF spatiotemporal organization, resulting in model-specific characteristics of AF. With frequency domain analysis of electrograms acquired from high-density optical mapping, AF from the right (RA) and left (LA) atrium in animals with RAP and MR were compared with control animals. At follow-up, the hearts were excised and perfused, and optical action potentials were recorded from a 2 x 2-cm area each of the RA and LA free wall with a 16 x 16 photodiode array. AF was induced with extra stimuli, several 2.4-s AF episodes were recorded in each dog, and a fast Fourier transform was calculated. The dominant frequency (DF) was determined, and the organization (organization index, OI) was calculated as the ratio of the area under the dominant peak and its harmonics to the total area of the spectrum. All possible pairs of electrograms for each episode were cross-correlated. LA AF in the chronic MR model showed an increase in the highest DF, the number of DF domains, and in frequency gradient compared with AF in control or RAP models. In addition, there was a decrease in OI and in the correlation coefficients in the LA of the MR model. These results suggest that the AF substrate in the MR model may be different from that of control or RAP models.

Animals↗