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PubMed2006

Fine spatiotemporal structure of phase in human intracranial EEG.

OBJECTIVE: To transfer to the clinic for humans the technology and theory for high-resolution EEG analysis that have been developed in the laboratory with animals. METHODS: EEGs were recorded at high spatial resolution from a 1 x 1 cm 8 x 8 electrode array on the right inferior temporal gyrus of a patient undergoing preoperative monitoring for epilepsy surgery. Cosines were fitted to EEG segments to measure frequency and phase and compute location, size, latency, phase velocity, duration, and recurrence rate of radially symmetric spatial patterns called phase cones. The Hilbert transform was also used to get high temporal resolution. RESULTS: In the awake state, the power spectral density (PSD) showed power-law decrease in log power with log frequency at 1/falpha, alpha approximately 2, but with peaks in the standard empirical ranges. The phase in beta and gamma ranges had spatial gradients in conic form. Resetting of these stable spatial patterns of phase cones was spatially coincident at intermittent discontinuities ('phase slip') recurring at theta rates. Cones had half power diameters from 2 to 50+ mm; their durations had power-law distributions with values ranging from 6 to 300+ ms depending on length of the analysis window. In slow wave sleep PSD decreased at 1/falpha, alpha approximately 3,with loss of beta-gamma spectral peaks and diminished or absent oscillations and spatiotemporal phase structure. CONCLUSIONS: Spatiotemporal structures in awake human and rabbit EEG showed striking similarities. The only clear differences were ascribable to differing scales of measurement. These fine spatiotemporal structures of EEG were diminished or lost in slow wave sleep. SIGNIFICANCE: The fine structure indicates that neocortical stability is sustained at self-organized criticality; that synaptic input in the awake state drives neocortex away from criticality causing beta-gamma oscillations in re-stabilizing 'neural avalanches'; and that diminished input in slow wave sleep allows return toward criticality but with some added risk of instability and seizure.

Adult↗
PubMed2002

Effects of stimulus material on the Fröhlich illusion.

In the Fröhlich illusion, judgements of the first position of a moving object are typically displaced in the direction of motion. The illusion has been obtained with linear motion of a small target, and with rotary motion of a spatially extended line. We compared judgements of the initial orientation of a small dot and a line that rotated around the point of fixation. The illusion was absent with the dot, whereas it was reliably obtained with the line. When the density of the line was reduced to two dots, the illusion persisted. However, the illusion was absent when a half-line extending to only one side from fixation was presented. We discuss the results with respect to two attentional accounts of the Fröhlich illusion and an account based on spatiotemporal integration.

Adult↗
PubMed2006

Quantification of cross correlations in complex spatiotemporal systems.

We propose a design of the equal time correlation matrix suitable for the analysis of multivariate time series with ill-defined phases. We present the cross-correlation analysis of model data sets taken from coupled stochastic oscillators and compare the concept with the results obtained from a conventional correlation matrix analysis. We show that the concept provides a higher sensitivity combined with a better statistical significance when quantifying weak cross correlations.

Journal Article↗
PubMed2003

Increasing the efficiency of fuzzy logic-based gene expression data analysis.

DNA microarray technology can accommodate a multifaceted analysis of the expression of genes in an organism. The wealth of spatiotemporal data generated by this technology allows researchers to potentially reverse engineer a particular genetic network. "Fuzzy logic" has been proposed as a method to analyze the relationships between genes and help decipher a genetic network. This method can identify interacting genes that fit a known "fuzzy" model of gene interaction by testing all combinations of gene expression profiles. This paper introduces improvements made over previous fuzzy gene regulatory models in terms of computation time and robustness to noise. Improvement in computation time is achieved by using a cluster analysis as a preprocessing method to reduce the total number of gene combinations analyzed. This approach speeds up the algorithm by a factor of 50% with minimal effect on the results. The model's sensitivity to noise is reduced by implementing appropriate methods of "fuzzy rule aggregation" and "conjunction" that produce reliable results in the face of minor changes in model input.

Animals↗
PubMed2001

The flash-lag effect as a spatiotemporal correlation structure.

The flash-lag effect refers to the phenomenon in which a flash adjacent to a continuously moving object is perceived to lag behind it. Phenomenally, the flash appears to be spatially shifted relative to the moving stimulus, and the amount of lag has often been quantified as the flash's nulling position, which is the physical spatial offset needed to establish perceptual alignment. The present study offers a better way to summarize flash-lag data. Instead of plotting data in terms of space, the psychometric function of the observer's relative-position judgment is drawn on spatiotemporal plot. The psychological process underlying illusory lag is formulated as spatiotemporal bias and uncertainty and their estimate as a spatiotemporal convolution kernel that best explains the spatiotemporal psychometric function. Two empirical procedures of kernel estimation are described. One procedure is to fit the free parameters of the kernel to experimental data for continuous motion trajectory. The second is to give an analytical solution to the kernel using experimental data for random motion trajectory. The two procedures yield similar kernels, with negligible spatial bias and uncertainty and substantial temporal bias and uncertainty. In addition, it is demonstrated that an experimental manipulation of temporal predictability of the flash can change the temporal bias in the estimated kernel. The results of this novel analysis reveal that the flash-lag effect is viewed as a spatiotemporal correlation structure, which is largely characterized by the tendency to compare the position of the flash in the past with the position of the moving item in the present.

Humans↗
PubMed1994

Spatiotemporal response properties of direction-selective neurons in the nucleus of the optic tract and dorsal terminal nucleus of the wallaby, Macropus eugenii.

1. The spatial and temporal response characteristics of direction-selective neurons in the nucleus of the optic tract and dorsal terminal nucleus of the accessory optic system (NOT-DTN) of the wallaby were established using moving sinusoidal gratings. This is the first comprehensive investigation of the spatiotemporal response characteristics of NOT-DTN neurons in any species. 2. The analysis revealed two main classes of cells. The first class, referred to as slow neurons, are maximally sensitive to motion at low temporal frequencies (< 1 Hz) and high spatial frequencies (0.5-1.0 cpd). The second class, referred to as fast neurons, are most sensitive to motion at high temporal frequencies (> 10 Hz) and moderate to low spatial frequencies (0.1-0.5 cpd). The fast neurons also have a domain of high sensitivity at low temporal frequencies and high spatial frequencies. As the neurons are tuned to specific temporal frequencies of motion, rather than image velocities, it is suggested that the motion detectors are of the delay-and-compare type and code local motion-related changes in contrast or luminance. 3. Both classes of neuron are highly direction-selective in the midranges of their spatiotemporal tuning curves, i.e., the firing rates increase during motion in the preferred direction (temporonasal movement through the visual field of the contralateral eye) and decrease during motion in the opposite direction. At high temporal and low spatial frequencies, however, the slow neurons are inhibited by motion in both directions along their preferred axis. It is argued that this bidirectional inhibition at high speeds may act to inhibit ocular following during saccades and may act as a gain control mechanism preventing excessive overshoot in eye velocity at motion onset, when retinal-slip velocities are high. 4. The fast neurons probably have two functions. First, they are suited to initiating ocular following responses when image motion is quite fast. Second, their spatiotemporal tuning makes them candidates for supplying a velocity error signal into the velocity storage mechanism, which is most prominent at high stimulus speeds. 5. Fourier analysis of the peristimulus time histograms derived from the response of both the slow and fast neurons revealed that the main frequency components of the responses occurred at the fundamental and second harmonic frequencies of the input signal at low stimulus temporal frequencies (< 3.04 Hz). At higher stimulus frequencies, the responses contained significant frequency components at higher odd-harmonics of the input signal.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1998

A novel method for studying population health impacts of spatiotemporal ozone distribution.

This work is concerned with the development of a method to study the impact of ozone exposure on human health. The analysis is based on random field representations of exposure variation and health damage uncertainty in a composite space/time continuum, which previous studies did not allow. Ozone exposure-health damage is considered as a spatiotemporal holistic system, by looking at the whole picture, not just certain isolated parts. Ozone maps over the eastern United States provide the basic Framework for studying exposure-health relationships, that focus on a community wise basis. Composite space/time maps of health damage indicators associated with the ozone exposure levels are obtained. These maps constitute an important part of many health studies, offering a valuable description of the data and an important basis for further analysis. Health damage maps can identify, for example, regions over the eastern United States that will respond in certain ways to variation of ozone levels or the application of health management practices. Application areas are identified for future study.

Air Pollution↗
PubMed2006

Alternative approach to modal gait analysis through the Karhunen-Loève decomposition: An application in the sagittal plane.

This article uses the Karhunen-Loève decomposition (KL) technique, also known as proper orthogonal decomposition (POD) or principal component analysis (PCA), to introduce the concept of gait mode, which can be used as a tool to identify gait differences among subjects or groups and to approximate gait curves. The KL is a statistical pattern analysis technique for finding dominant structures in an ensemble of data. This technique can be used to decompose a spatiotemporal signal into time-independent, orthogonal, spatial components and time-dependent amplitudes. This study demonstrates the existence of a common gait mode through the analysis of the kinematics of 57 young, healthy subjects, and how they can be used to identify different walking patterns, for instance differentiating male and female subjects.

Biomechanical Phenomena↗
PubMed1994

Stage- and region-dependent chondrogenesis and growth of chick wing-bud mesenchyme in serum-containing and defined tissue culture media.

During development, limb-bud mesenchymal cells carry out complex spatiotemporal-patterns of growth and differentiation. Tissue and organ culture facilitate analysis of environmental influences on these cell behaviors, allowing their partial dissection into exogenous and endogenous components. Two factors that complicate such in vitro analyses are the heterogeneity of the cultured cells and imprecise knowledge of culture medium composition. Limb mesenchyme comprises a heterogenous cell population with important regional differences in cell type. Dividing the limb into subregions helps limit the cellular heterogeneity and using chemically defined, serum-free medium alloys concerns about medium composition. In the present study, mesenchyme from different regions along the anteroposterior and proximodistal axes of stage 21-22 and stage 23-24 chick wing buds was grown in high-density microtiter cultures in chemically defined and in serum-containing medium. Four-day cultures of the various regions were compared in terms of culture morphology and the accumulation of Alcian blue-positive cartilage matrix and DNA. The results demonstrate stage- and region-dependent differences in the in vitro growth, differentiation, and responsiveness of these cells. For example, mesenchyme from the distal anterior region of the wing bud exhibited lower intrinsic chondrogenic capacity and greater responsiveness to serum than other regions. Patterns of in vitro chondrogenesis also suggest that, at the stages examined, distal wing-bud mesenchyme may be less homogeneous than has been believed. A case is made for the suitability of serum-free medium for future in vitro studies of chick limb-bud mesenchyme. The results are considered in relation to the process of limb development and regional expression of pattern-related genes.

Animals↗
PubMed2006

DiGeorge syndrome and pharyngeal apparatus development.

DiGeorge syndrome is the most frequent microdeletion syndrome in humans, and is characterized by cardiovascular, thymic and parathyroid, and craniofacial anomalies. The underlying cause is disturbed formation of the pharyngeal apparatus, a transient structure present during vertebrate development that gives rise to endocrine glands, craniofacial tissue, and the cardiac outflow tract. The pharyngeal apparatus is composed of derivatives of ectoderm, endoderm, mesoderm and the neural crest. Thus, complex interactions between cell types from different origins have to be orchestrated in the correct spatiotemporal manner to establish proper formation of the pharyngeal system. The analysis of engineered mouse mutants developing a phenotype resembling DiGeorge syndrome has revealed genes and signalling pathways crucial for this process. Intriguingly, these mouse models reveal that interference with either of two distinct phases of pharyngeal apparatus development can contribute to the aetiology of DiGeorge syndrome.

Animals↗
PubMed1993

Fading time of retinally-stabilized images as a function of background luminance and target width.

Fading time of a retinally-stabilized difference-of-Gaussian (DOG) stimulus depends on the background luminance, contrast and spatial frequency content of the stimulus. A model of the visual system including a nonlinear multiplicative, non-local and fast process followed by a linear subtractive, local and slower process accounts for these effects. Analysis of the fading time data allows us to estimate the spatiotemporal characteristics of the proposed adaptation processes. The model is consistent with recent models of normal light adaptation from the probe-flash paradigm.

Adaptation, Ocular↗
PubMed1999

Instabilities of cavity solitons in optical parametric oscillators.

Using an example of cavity solitons in optical parametric oscillators it is demonstrated that Hopf instability of these dissipative structures can be directly associated with internal modes of their conservative counterparts. The latter ones are free propagating quadratic solitons in this case. Linear stability analysis and numerical simulation also reveal multistability and complex instability induced spatiotemporal dynamics of single and multihump cavity solitons.

Journal Article↗
PubMed2000

Detection of fixed points in spatiotemporal signals by a clustering method.

We present a method to determine fixed points in spatiotemporal signals. The method combines a clustering algorithm and a nonlinear analysis method fitting temporal dynamics. A 144-dimensional simulated signal, similar to a Kueppers-Lortz instability, is analyzed and its fixed points are reconstructed.

Algorithms↗
PubMed2005

Role of Fabp7, a downstream gene of Pax6, in the maintenance of neuroepithelial cells during early embryonic development of the rat cortex.

Pax6 is a transcription factor with key functional roles in the developing brain. Pax6 promotes neuronal differentiation via transcriptional regulation of the Neurogenin2 (Ngn2) gene, although Pax6 expression appears in proliferating neuroepithelial cells before the onset of neurogenesis. Here, we identified Fabp7 (BLBP/B-FABP), a member of the fatty acid-binding protein (FABP) family, as a downregulated gene in the embryonic brain of Pax6 mutant rat (rSey2/rSey2) by microarray analysis. Marked reduction of Fabp7 expression was confirmed by quantitative PCR. Spatiotemporal expression patterns of Fabp7 in the wild-type rat embryos from embryonic day 10.5 (E10.5) to E14.5 were similar to those of Pax6, and expression of Fabp7 was undetectable in the rSey2/rSey2 cortex. The expression pattern of Fabp7 in the wild-type mouse embryo at E10.5 (corresponding to E12.5 rat) was different from that in the rat embryo, and no change of expression was observed in the Sey/Sey mouse embryo. Overexpression of exogenous Pax6 mainly induced ectopic expression of Fabp7, rather than of Ngn2, in the early cortical primordium. Interestingly, knocking-down FABP7 function by electroporation of Fabp7 small interfering RNA severely curtailed cell proliferation but promoted neuronal differentiation. We conclude that Fabp7 is a downstream gene of Pax6 transcription factor in the developing rat cortex and essential for maintenance of neuroepithelial cells during early cortical development.

Animals↗
PubMed2000

[Field potential recording for investigation of synaptic plasticity in vitro].

The in vitro brain slice preparations have been widely employed for investigation of the cellular mechanisms underlying long-term potentiation and long-term depression of synaptic transmission in the rodent hippocampus. The determination of spatiotemporal patterns of activation by means of current source-density analysis of evoked field potentials allows for the use of field potential recording in the research on neocortical synaptic plasticity, in particular in horizontal connections of the motor cortex.

Animals↗
PubMed2003

Optical analysis of acute spontaneous epileptiform discharges in the in vivo rat cerebral cortex.

We examined the spatiotemporal patterns of spontaneous epileptiform activity observed in the in vivo rat cerebral cortex using an optical recording technique of detecting transmembrane voltage changes. The surface of the cerebral cortex was exposed under anesthesia and stained with a fluorescent voltage-sensitive dye, RH414. Acute spontaneous epileptiform discharges were induced by application of a GABA(A) receptor antagonist, bicuculline. Changes in the intensity of fluorescence were recorded from the cerebral cortex using a 464-channel optic fiber photodiode system. We succeeded in recording spontaneous epileptiform discharges, and constructed their initiation-site maps. We found that the initiation site was neither unique nor randomly located, but exhibited a multimodal distribution pattern. The incidence of epileptiform discharges was different between the initiation sites, and some sites showed dominance in the induction of spontaneous epileptiform discharges.

Animals↗
PubMed2000

Analysis of arm trajectories of everyday tasks for the development of an upper-limb orthosis.

Spatiotemporal arm and body movements of able-bodied subjects performing nine everyday tasks were recorded for the purpose of guiding the development of an upper-limb orthosis. To provide a user the opportunity to carry out these tasks with natural movements, the orthosis should allow replication of the measured trajectories. We outline the orthosis architecture, which supports the user's upper arm and forearm, and analyze the movement data to obtain orthosis design specifications. Trajectories were obtained using six-degree-of-freedom magnetic position sensors affixed to the wrist, elbow, shoulder, trunk and head. Elbow trajectory data were decomposed into ranges along the principle Cartesian axes to provide a generally useful envelope measure. The smallest Cartesian parallel-piped that contained the elbow trajectories for most tasks was approximately 30 cm front/back, 15 cm side/side, and 17 cm up/down. A rough lower bound estimate obtained by asking subjects to repeat the tasks while minimizing elbow movement substantially reduced movement in the up/down and side/side dimensions. Elbow angles were generally in the range 50 degrees-150 degrees, and the angle of the forearm with respect to vertical was 10 degrees-110 degrees. Raw trajectory data may be downloaded from www://asel.udel.edu/robotics/orthosis/range.h tml.

Activities of Daily Living↗
PubMed1995

Current source density analysis of the electroretinographic d wave of frog retina.

1. Dark flashes were used to evoke spatiotemporal profiles of the d wave of the electroretinogram in frog retina. The current source density technique was used to compute the extracellular current sinks and sources underlying the d wave. 2. The largest d wave current was a sink at the outer plexiform layer (OPL sink) and a source at the inner plexiform layer (IPL source). Several properties of this sink/source, including its relative insensitivity to Ba2+, suggest that it arises from hyperpolarizing bipolar cells. 3. There was a slower IPL sink, along with a source at the inner limiting membrane (ILM source). Its properties, along with its sensitivity to Ba2+ and enhancement by picrotoxin, suggest it arises from the K+ spatial buffer currents of Müller cells. This IPL sink/ILM source underlies the M wave. 4. A small photoreceptor sink/source also contributes to the d wave. This is most significant during the very beginning of the d wave. 5. Our results indicate that in frog retina and at the stimulus conditions used in this paper, the d wave originates primarily and directly from the hyperpolarizing bipolar cells. Photoreceptors likely contribute a small amount, especially during the initial portion of the d wave. There is possibly a small Müller cell contribution.

Animals↗