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PubMed2005

Quantitative reassessment of speed tuning in the accessory optic system and pretectum of pigeons.

The correlation model of motion detection has been used to describe visual motion processing in the pretectum and accessory optic system (AOS). One feature of correlation detectors is that they are tuned to a particular temporal frequency (TF) independent of the spatial frequency (SF) but not to a particular stimulus speed (speed = TF/SF). Previous work has suggested that a subset of neurons in the AOS and pretectum of pigeons show apparent speed tuning. However, this study used relatively liberal between-groups statistics to assess speed tuning. From studies of the motion-sensitive neurons in primate cortex, a rigorous within-groups test of speed tuning has been offered. A meta-analysis of the spatiotemporal tuning of units in the AOS and pretectum of pigeons using this within-groups analysis of speed tuning has been performed. We conclude that speed tuning in the AOS and pretectum is rarer than previously estimated, and there is remarkable diversity in the impact of SF on tuning for speed. In total, 18.6% of the units showed significant speed tuning whereas 39.8% showed significant SF/TF independence. However, many cells (41.5%) fell along a continuum between speed tuning and SF/TF independence. This diversity has also been noted in primate cortex and may reflect a general property of motion-sensitive systems.

Algorithms↗
PubMed2004

The spatiotemporal precision of ganglion cell signals: a comparison of physiological and psychophysical performance with moving gratings.

Comparison of the spatiotemporal information delivered by ganglion cells with human psychophysical performance may give insight to how retinal information is utilized by cortical mechanisms, and constrain models of spatiotemporal processing. Ganglion cells' responses were measured with drifting gratings of various spatial and temporal frequencies and contrasts. The spatiotemporal precision of cell responses was estimated in terms of a noise measure and phase variation, and compared to human vernier performance. Noise and phase variation of magnocellular (MC) cells was least at low temporal frequencies, despite their transient responses. The patterns of spatiotemporal precision of MC cells resembled the patterns of human vernier thresholds while those of parvocellular cells did not, implying use of MC cells' signals in these tasks. The analysis further implied that cortical mechanisms must perform a sophisticated spatiotemporal analysis over local ganglion cell arrays.

Animals↗
PubMed1997

Development of spatiotemporal receptive fields of simple cells: II. Simulation and analysis.

In part I of this article a correlation based model for the developmental process of spatiotemporal receptive fields has been introduced. In this model the development is described as an activity-dependent competition between four types of input from the lateral geniculate nucleus onto a cortical cell, viz. non-lagged ON and OFF and lagged ON and OFF inputs. In the present paper simulation results and a first analysis are presented for this model. We study the developmental process both before and after eye-opening and compare the results with experimental data from reverse correlation measurements. The outcome of the developmental process is determined mainly by the spatial and the temporal correlations between the different inputs. In particular, if the mean correlation between non-lagged and lagged inputs is weak, receptive fields with a widely varying degree of direction selectivity emerge. However, spatiotemporal receptive fields may show rotation of their preferred orientation as a function of response delay. Even if the mean correlation between two types of temporal input is not weak, direction-selective receptive fields may emerge because of an intracortical interaction between different cortical maps. In an environment of moving lines or gratings, direction-selective receptive fields develop only if the distribution of the directions of motion presented during development shows some anisotropy. In this case, a continuous map of preferred direction is also shown to develop.

Algorithms↗
PubMed2002

Spatiotemporal dynamics of contact activation factors of blood coagulation.

A new in vitro model is proposed for studying the spatiotemporal distributions of activated clotting factors, in which clotting is activated in a thin layer of non-stirred plasma supplemented with a fluorogenic substrate and is monitored by fluorescence from its cleavage product. Analysis of the spatiotemporal dynamics of factor XIa and kallikrein in glass-activated human plasma provides evidence that both contact factors remain restricted to the glass surface and possibly a narrow boundary zone (<0.1 mm). The kinetics of factor XIa and kallikrein studied by a new method (in non-stirred plasma) coincided with those studied fluorimetrically with full stirring: their concentrations rapidly rose for the first few minutes after activation and then slowly declined. Factor XI and prekallikrein activation is likely to be restricted by the limited number of sites available for binding to the surface. The maximum concentration of the active factors was estimated at 2 x 10(8) molecules per mm(2) at the glass surface (irrespective of stirring). At the plastic surface, this value was 15--30 times lower.

Algorithms↗
PubMed2004

Gender differences in three dimensional gait analysis data from 98 healthy Korean adults.

OBJECTIVES: The research hypothesis was that healthy adults would walk differently according to their gender when walked barefoot at their comfortable speed. The aim of this study was to prove the hypothesis in healthy Korean adults. DESIGN: Between-gender statistical comparisons of the gait analysis data including spatiotemporal, three-dimensional joint kinematic and kinetic data. BACKGROUND: There have been few attempts to identify the significant gender differences in gait pattern and to explore their possible causes. METHODS: Healthy 98 Korean adults (47 females and 51 males) volunteered. Gait analysis data was obtained with opto-electric system and force plates. Normalization was used to avoid the body size effect. Gender difference was tested with independent t-test, ancova, and two-way repeated anova. RESULTS: Females were shorter, both in height and leg length ( P < 0.05 ). The cadence and pelvic width were as great as in males. They walked slower than males due to shorter stride length ( P < 0.05 ). The females had still shorter stride length and narrower step width ( P < 0.05 ), and they walked as fast as the males. Females walked with their pelvis tilted more anteriorly and more up and down oblique motion, hip joints more flexed-adducted-internally rotated, knee joint in more valgus angles ( P = 0.05 ). CONCLUSIONS: The gait analysis data had significant gender differences. We assume that the difference is due to gender features of the gait-related anatomy and habits. Comparison with other research shows some evidence for racial differences.

Adult↗
PubMed2005

Spatiotemporal pattern of the extracranial component of the rheoencephalographic signal.

The use of rheoencephalography (REG) in the clinical practice to evaluate cerebral blood flow is conditional on the finding of a method for removing the extracranial interference caused by the scalp blood flow. To remove this undesirable influence, digital processing based on statistics could be an effective technique if the appropriate data model were applied. This paper focuses on the analysis of the spatiotemporal features of the extracranial REG component, by comparing its morphology and phase shift at several scalp sites. For this purpose, a numerical model of the scalp was employed to assess tissue impedance changes caused by the inflow of a stepwise blood pulse wave. These results were compared with the experimental impedance waveforms recorded on six pairs of adjacent electrodes. The correlation coefficients between each pair of impedance recordings of each subject were always greater than 0.942, showing a mean value of 0.986. This result suggests that the extracranial REG component can be considered as morphologically invariant. On the other hand, negligible phase shifts were observed when mean electrode distances, measured in the blood flow direction, were relatively small, although temporal corrections in the data model would be advisable for longer distances.

Adult↗
PubMed2004

Isometric graphing and multidimensional scaling for reaction-diffusion modeling on regular and fractal surfaces with spatiotemporal pattern recognition.

Heterogeneous surface reactions exhibiting complex spatiotemporal dynamics and patterns can be studied as processes involving reaction-diffusion mechanisms. In many realistic situations, the surface has fractal characteristics. This situation is studied by isometric graphing and multidimensional scaling (IGMDS) of fractal surfaces for extracting geodesic distances (i.e., shortest scaled distances that obtain edges of neighboring surface nodes and their interconnections) and the results obtained used to model effects of surface diffusion with nonlinear reactions. Further analysis of evolved spatiotemporal patterns may be carried out by IGMDS because high-dimensional snapshot data can be efficiently projected to a transformed subspace with reduced dimensions. Validation of the IGMDS methodology is carried out by comparing results with reduction capabilities of conventional principal component analysis for simple situations of reaction and diffusion on surfaces. The usefulness of the IGMDS methodology is shown for analysis of complex patterns formed on both regular and fractal surfaces, and using generic nonlinear reaction-diffusion systems following FitzHugh Nagumo and cubic reaction kinetics. The studies of these systems with nonlinear kinetics and noise show that effects of surface disorder due to fractality can become very relevant. The relevance is shown by studying properties of dynamical invariants in IGMDS component space, viz., the Lyapunov exponents and the KS entropy for interesting situations of spiral formation and turbulent patterns.

Diffusion↗
PubMed1982

Visual processing deficits in acute and chronic schizophrenics.

Psychophysical techniques have been used to assess the duration that brief visual stimuli remain in visual memory. At the earliest "iconic" stage the duration depends on several parameters, one of which is spatial frequency. In the present experiment, a two-pulse temporal resolution task was used to evaluate the duration of iconic persistence in schizophrenics as a function of spatial frequency. Normal controls, acute, and chronic schizophrenics viewed achromatic gratings of different spatial frequencies. Their objective was to discriminate between a single or double flash of these gratings. Signal detection analysis was used to control for psychological factors. Repeated measures analyses of variance revealed that schizophrenics (i) do not conform to the typical relationship between iconic persistence and spatial frequency of the grating and (ii) have longer iconic persistence than normals on all spatial frequencies. The results are discussed in terms of the different sensitivities of transient and sustained neurophysiological mechanisms involved in spatiotemporal frequency visual analysis.

Adolescent↗
PubMed2001

Spatiotemporal expression of otogelin in the developing and adult mouse inner ear.

Using a PCR-based subtractive method on cDNA from 2-day-old mouse cochlea, we identified a gene encoding otogelin, Otog, an inner ear specific glycoprotein expressed in all acellular structures. Here, we provide evidence that otogelin is detected as early as embryonic day 10 in the otic vesicle. At this stage, otogelin is detected in the epithelial cells which do not overlap with the myosin VIIA-expressing cells, namely the precursors of the hair cells, thus arguing for an early commitment of the two cell populations. Analysis of otogelin spatiotemporal cell distribution allows a molecular tracing for the contribution of the cochlear and vestibular inner ear supporting cells to the formation of the acellular structures. Throughout embryonic and adult life, the expression of the otogelin gene as monitored by LacZ inserted into Otog, and the abundance of the protein are greater in the vestibule than in the cochlea. In adult, otogelin is still produced by the vestibular supporting cells, which argues for a continuous process of otogelin renewal in the otoconial membranes and cupulae. In contrast, in the tectorial membrane, otogelin should be a long-lasting protein since both the otogelin gene and protein were almost undetectable in adult cochlear cells. The data are consistent with the requirement for otogelin in the attachment of the otoconial membranes and cupulae to their corresponding sensory epithelia as revealed in Otog -/- mice.

Aging↗
PubMed1996

Dipole source analysis suggests selective modulation of the supplementary motor area contribution to the readiness potential.

The readiness potential preceding voluntary movement is modulated by the mode of movement selection, i.e. it has a higher amplitude preceding freely selected than before prescribed movements (Praamstra, P., Stegeman, D.F., Horstink, M.W.I.M., Brunia, C.H.M. and Cools, A.R. Movement-related potentials preceding voluntary movement are modulated by the mode of movement selection. Exp. Brain Res., 1995, 103: 429-439). One cortical area that is likely to be involved in this modulation is the supplementary motor area (SMA). Recent attempts to elucidate the neural generators of the readiness potential using spatiotemporal dipole source analysis, however, failed to establish a significant SMA contribution to the readiness potential. This might be explained by a failure of the proposed analyses to discriminate between SMA and motor cortex contributions to the readiness potential. We applied a dipole source analysis approach that better separates these overlapping source activities. The resulting source model includes an SMA source generating pre-movement activity consistent with evidence from intracranial recordings in humans. The SMA source accounts almost completely for the modulation of the readiness potential by different modes of movement selection. On the basis of these results, the relation between scalp-recorded movement-related activity, intracranially recorded potentials, and findings from functional imaging studies of voluntary movement, appears more transparent than suggested by previous dipole source analyses of premovement potentials.

Adult↗
PubMed2004

Intersubject synchronization of cortical activity during natural vision.

To what extent do all brains work alike during natural conditions? We explored this question by letting five subjects freely view half an hour of a popular movie while undergoing functional brain imaging. Applying an unbiased analysis in which spatiotemporal activity patterns in one brain were used to "model" activity in another brain, we found a striking level of voxel-by-voxel synchronization between individuals, not only in primary and secondary visual and auditory areas but also in association cortices. The results reveal a surprising tendency of individual brains to "tick collectively" during natural vision. The intersubject synchronization consisted of a widespread cortical activation pattern correlated with emotionally arousing scenes and regionally selective components. The characteristics of these activations were revealed with the use of an open-ended "reverse-correlation" approach, which inverts the conventional analysis by letting the brain signals themselves "pick up" the optimal stimuli for each specialized cortical area.

Adult↗
PubMed1994

Dipole source analysis. Linking scalp potentials to their generating neuronal structures.

The spatiotemporal approach of dipole source analysis is a crucial methodological advance in event-related potential research, as overlapping subcomponents of cortical evoked potentials can be separated and related to their generating structures. This enhances the reliability and validity of event-related potential parameters and facilitates the link to underlying neurochemical processes. The present paper presents methodological aspects of the dipole source analysis of auditory-evoked potentials to different stimulus intensities.

Adult↗
PubMed2005

Secretion of type III effectors into host cells in real time.

Type III secretion (T3S) systems are key features of many gram-negative bacteria that translocate T3S effector proteins directly into eukaryotic cells. There, T3S effectors exert many effects, such as cellular invasion or modulation of host immune responses. Studying spatiotemporal orchestrated secretion of various effectors has been difficult without disrupting their functions. Here we developed a new approach using Shigella flexneri T3S as a model to investigate bacterial translocation of individual effectors via multidimensional time-lapse microscopy. We demonstrate that direct fluorescent labeling of tetracysteine motif-tagged effectors IpaB and IpaC is possible in situ without loss of function. Studying the T3S kinetics of IpaB and IpaC ejection from individual bacteria, we found that the entire pools of IpaB and IpaC were released concurrently upon host cell contact, and that 50% of each effector was secreted in 240 s. This method allows an unprecedented analysis of the spatiotemporal events during T3S.

Antigens, Bacterial↗
PubMedDate not supplied

Physical genome analysis of bacteria.

Pulsed-field gel electrophoresis (PFGE) is a general analytical tool to separate large DNA molecules and may therefore be applied to problems from all areas of bacteriology. The genome size of bacteria covers the range of 0.6 to 10 megabase pairs. For genome fingerprinting, the bacterial chromosome is cleaved with a restriction endonuclease that gives a resolvable and informative number of five to one hundred fragments on the PFGE gel. Restriction enzymes are chosen according to GC content, degree of methylation, and codon usage of the respective bacterial genus. Macrorestriction fingerprinting allows the identification of bacterial strains and the distinction between related and unrelated strains. If fragment patterns of several restriction digestions are quantitatively evaluated, strains can be classified according to genetic relatedness at the level of genus, species, and biovar. In particular, members of a clonal lineage can be uncovered. Hence, any problem from applied, environmental, and clinical microbiology may be addressed by PFGE restriction analysis where the spatiotemporal spread of a bacterial clone is of interest. In bacterial genomics, PFGE is employed for the top-down construction of macrorestriction maps of the chromosome which yields data about genome organization, mobile genetic elements, and the arrangement of gene loci and gene families. The genomic diversity of a bacterial species is elucidated by comparative chromosome mapping. Map positions of restriction sites and gene loci of interest serve as landmarks to assess the extent of gross chromosomal modification, namely insertions, deletions and inversions. Intra- and interspecies comparisons of genome organization provide insights into the structure and diversity of bacterial populations and the phylogeny of bacterial taxa.

Bacteria↗
PubMed1996

Avian olfactory receptors: differentiation of olfactory neurons under normal and experimental conditions.

The bird olfactory system has a simple structure and affords an attractive developmental model for the study of olfactory morphogenesis and differentiation. We have cloned and characterized several chick olfactory receptor (COR) genes belonging to the superfamily of seven-transmembrane domain proteins. In situ hybridization analysis of their spatiotemporal patterns of expression during development reveals several important characteristics. COR expression starts early in placodal cells (Embryonic Day 5, E5). Changes in their expression pattern then correlate with the onset of synaptogenesis (E8). The adult pattern, achieved before hatching, shows that cells expressing a particular COR are not regionalized within the epithelium. By double-label in situ hybridization, we clearly demonstrate that a single cell does not coexpress different COR genes (or subsets of CORs) at any stage of development. Following bulbar deafferentation, COR expression ceases more rapidly than expected from previous axotomy experiments. Concomitantly, a reactivation of the Cash-1 gene, which is involved in early neuronal specification, could be an early sign of olfactory neuronal regeneration. Modulation of COR and Cash-1 expression points to a simultaneous process of neuronal degeneration and regeneration in the olfactory epithelium after axotomy. COR expression is restricted to the olfactory epithelium except during early stages (before synaptogenesis). At that time, cells distributed along the olfactory nerve, from the placode to the anterior telencephalon, also express CORs. This cell population is different from the luteinizing hormone releasing hormone neurons migrating from the placode. Our results show that the olfactory neurons or neuroblasts choose to express one COR before establishing functional connections with the bulb. Later on, bulboepithelial connections seem important not only for olfactory neuron survival but also for stimulation of COR expression. In addition, beyond their implication in functional odor detection, CORs could be involved, at early stages, in processes of olfactory morphogenesis, including the establishment of a bulbar chemotopy.

Amino Acid Sequence↗
PubMed1999

Colinear and segmental expression of amphioxus Hox genes.

The cephalochordate amphioxus has a single Hox gene cluster. Here we describe the genomic organization of four adjacent amphioxus genes, AmphiHox-1 to AmphiHox-4, together with analysis of their spatiotemporal expression patterns. We demonstrate that these genes obey temporal colinearity and that three of the genes also obey spatial colinearity in the developing neural tube. AmphiHox-1, AmphiHox-3, and AmphiHox-4 show segmental modulation of their expression levels, a two-segment phasing of spatial colinearity, and, at least for AmphiHox-4, asymmetrical expression. AmphiHox-2 is unlike other amphioxus Hox genes: it does not obey spatial colinearity and it has no positional expression in the neural tube. AmphiHox-2 is expressed in the preoral pit of larvae, from which the homologue of the anterior pituitary develops. We suggest that the ancestral role of chordate Hox genes was primarily in the neural tube and that chordate Hox genes can functionally diverge in a manner analogous to that of Drosophila ftz or zen.

Amino Acid Sequence↗
PubMed2001

Zebrafish genes rx1 and rx2 help define the region of forebrain that gives rise to retina.

Zebrafish retinal homeobox genes rx1 and rx2 are expressed exclusively in the optic primordia and then in cone photoreceptors of the differentiated neural retina. In this study, we show that the rx expression domain is coextensive with the region identified as the retinal field in published fate maps of the neural plate in zebrafish embryos. Analysis of the spatiotemporal relationships between retinal and forebrain precursors suggests that lateral movement of retinal precursors is responsible for evagination of the optic primordia. Overexpression of either rx1 or rx2 results in the loss of forebrain tissue and the ectopic formation of retinal tissue. We asked whether the deletion of forebrain and expansion of retinal tissue could be explained by the death of telencephalic precursors and enhanced proliferation of retinal precursors, and we found that it could not. Instead, our data are consistent with a change in cell fate of forebrain precursors associated with reduced expression of telencephalic markers (emx1 and BF-1) and ectopic expression of retinal markers (rx1/2/3, pax6, six6, and vsx2) at the neural keel stage. The rx homeodomain alone is sufficient to induce ectopic retinal tissue, although weakly so, and this observation, together with results from deletion constructs, suggests that interactions with unidentified transcriptional regulators are important for rx1 and rx2 function during early eye development. We conclude that regulated expression of zebrafish rx1 and rx2 helps to define the region of the forebrain fated to give rise to retinal tissue and may be involved in the cellular migrations that lead to splitting of the retinal field and formation of the optic primordia.

Animals↗
PubMed2005

A field-theoretic approach to understanding scale-free neocortical dynamics.

A mesoscopic field-theoretic approach is compared with neural network and brain imaging approaches to understanding brain dynamics. Analysis of high spatiotemporal resolution rabbit electroencephalogram (EEG) reveals neural fields in the form of spatial patterns in amplitude (AM) and phase (PM) modulation of gamma and beta carrier waves that serve to classify EEGs from trials with differing conditioned stimuli (CS+/-). Paleocortex exemplified by olfactory EEG has one AM-PM pattern at a time that forms by an input-dependent phase transition. Neocortex shows multiple overlapping AM-PM patterns before and during presentation of CSs. Modeling suggests that neocortex is stabilized in a scale-free state of self-organized criticality, enabling cooperative domains to form virtually instantaneously by phase transitions ranging in size from a few hypercolumns to an entire hemisphere. Self-organized local domains precede formation of global domains that supervene and contribute global modulations to local domains. This mechanism is proposed to explain Gestalt formation in perception.

Animals↗