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[Spatial-temporal patterns of the cell cycles in embryos of the clawed toad during gastrulation and neurulation].

The dynamics of DNA synthesis and duration of G2-phases in different dorso-ventral zones and cell layers were studied using 3H-thymidine in the X. laevis embryos during gastrulation and neurulation. Gradients of the index of labelled nuclei and of the rate of 3H-thymidine incorporation decreasing in the ventro-dorsal direction were observed during the whole period of gastrulation. In the end of gastrulation a wave of increase of the index of labelled nuclei and of the rate of 3H-thymidine incorporation proceeds in the same direction and, as a result, both the gradients are inverted. A high positive correlation was found between the simultaneously registered indices of labelled nuclei in different cell layers of the same dorso-ventral zones. The data were obtained suggesting the ventro-dorsal migration of cells in G2-phase. A conclusion is drawn that the regulation of cell cycles during gastrulation--neurulation obeys integral laws among which the waves of cell entrance in S-phase play an important role.

Animals↗
PubMed1983

Shadows of thought: shifting lateralization of human brain electrical patterns during brief visuomotor task.

Dynamic spatial patterns of correlation of electrical potentials recorded from the human brain were shown in diagrams generated by mathematical pattern recognition. The patterns for "move" and "no-move" variants of a brief visuospatial task were compared. In the interval spanning the P300 peak of the evoked potential, higher correlations of the right parietal electrode with occipital and central electrodes distinguished the no-move task from the move task. In the next interval, spanning the readiness potential in the move task, higher correlations of the left central electrode with occipital and frontal electrodes characterized the move task. These results conform to neuropsychological expectations of localized processing and their temporal sequence. The rapid change in the side and site of localized processes may account for conflicting reports of lateralization in studies which lacked adequate spatial and temporal resolution.

Adult↗
PubMed1990

The effects of temporal modulation and spatial location on the perceived spatial frequency of visual patterns.

The perceived spatial frequency of a visual pattern can increase when a pattern drifts or is presented at a peripheral visual field location, as compared with a foveally viewed, stationary pattern. We confirmed previously reported effects of motion on foveally viewed patterns and of location on stationary patterns and extended this analysis to the effect of motion on peripherally viewed patterns and the effect of location on drifting patterns. Most central to our investigation was the combined effect of temporal modulation and spatial location on perceived spatial frequency. The group data, as well as the individual sets of data for most observers, are consistent with the mathematical concept of separability for the effects of temporal modulation and spatial location on perceived spatial frequency. Two qualitative psychophysical models suggest explanations for the effects. Both models assume that the receptive-field sizes of a set of underlying psychophysical mechanisms monotonically change as a function of temporal modulation or visual field location, whereas the perceptual labels attached to a set of channels remain invariant. These models predict that drifting or peripheral viewing of a pattern will cause a shift in the perceived spatial frequency of the pattern to a higher apparent spatial frequency.

Adult↗
PubMed1991

Cocaine: on-line analysis of an accumbens amine neural basis for psychomotor behavior.

Dose-response studies on subcutaneous cocaine were done to ascertain its effects in nucleus accumbens in dopaminergic and serotonergic neuronal circuitry in the behaving rat with in vivo voltammetry. Simultaneously, and at each dose of cocaine, unconditioned psychomotor stimulant behavior induced by cocaine was studied in terms of multiple concurrent measures of spontaneous behavior and by activity pattern analysis, a study of spatial patterns of locomotion. Time course studies showed that the neurochemical effects of cocaine (10, 20, and 40 mg/kg SC) significantly (p less than 0.0001) increased accumbens synaptic concentrations of dopamine (DA) and concurrently and significantly (p less than 0.0001) decreased accumbens synaptic concentrations of serotonin (5-HT) in a dose response manner. Simultaneous behavioral time course studies showed that cocaine (10, 20, and 40 mg/kg SC) significantly (p less than 0.0001) increased ambulations (locomotor activity), fine movements (stereotypic movements of sniffing and grooming) and rearing behavior, while significantly decreasing agoraphobic behavior, as measured by a statistically significant increase in central ambulations (p less than 0.0001). The high dose of cocaine (40 mg/kg SC) significantly increased fine movements over those produced by the lower doses of cocaine (p less than 0.0002). One import of the findings is that the DA and 5-HT biogenic amine response occurs in a behavioral paradigm of psychomotor stimulation, which is a known measure of reinforcement. Another is that the biogenic amines DA and 5-HT are affected by cocaine in this reinforcement paradigm with exactly opposite directionality. Finally, acute cocaine administration is shown to produce a dose response inhibition of agoraphobia (fear), which is highly correlated (p = .983, p less than 0.01) with the opposing effects of cocaine on the accumbens biogenic amines, DA and 5-HT.

Animals↗
PubMed1992

Assessing short-term recognition memory with forced-choice psychophysical methods.

The rationale and methodology for using computer-controlled forced-choice psychophysical methods to assess short-term recognition memory in human subjects are presented. Here, we use non-verbal computer-synthesized auditory and visual stimuli with an adaptive psychophysical procedure. Sequence-length thresholds (SLTs, span lengths) for randomly generated binary auditory and visual-sequential patterns and simultaneous visual-spatial patterns are determined to assess short-term memory capacity. The SLTs can also be used to equate for initial retention level for delayed matching-to-sample (DMS) or delayed matching-to-non-sample (DMNS) tasks which assess memory decay. The DMS/DMNS tasks have also been modified for use with the forced-choice paradigm. In contrast to many verbal paradigms requiring immediate ordered recall, non-verbal stimuli in a forced-choice paradigm provide a more direct measure of sensory memory because long-term memory, complex encoding/decoding processes, and motor-sequencing factors are minimized or avoided. Furthermore, the forced-choice recognition memory tasks are applicable over a broad age range, are less sensitive to socio-economic factors and educational level, and avoid complex instructions. Taken together, these factors enhance the applicability of these tasks in children and adults with CNS lesions, particularly where cognitive status may be compromised.

Acoustic Stimulation↗
PubMed1983

Vibrotactile identification of vowels.

The ability of subjects to identify vowels in vibrotactile transformations of consonant-vowel syllables was measured for two types of displays: a spectral display (frequency by intensity), and a vocal tract area function display (vocal tract location by cross-sectional area). Both displays were presented to the fingertip via the tactile display of the Optacon transducer. In the first experiments the spectral display was effective for identifying vowels in /b/V/ context when as many as 24 or as few as eight spectral channels were presented to the skin. However, performance fell when the 12- and 8-channel displays were reduced in size to occupy 1/2 or 1/3 of the 24-row tactile matrix. The effect of reducing the size of the display was greater when the spectrum was represented as a solid histogram ("filled" patterns) than when it was represented as a simple spectral contour ("unfilled" patterns). Spatial masking within the filled pattern was postulated as the cause for this decline in performance. Another experiment measured the utility of the spectral display when the syllables were produced by multiple speakers. The resulting increase in response confusions was primarily attributable to variations in the tactile patterns caused by differences in vocal tract resonances among the speakers. The final experiment found an area function display to be inferior to the spectral display for identification of vowels. The results demonstrate that a two-dimensional spectral display is worthy of further development as a basic vibrotactile display for speech.

Communication Devices for People with Disabilities↗
PubMed1991

Morphogenesis and territorial coverage by isolated mammalian retinal ganglion cells.

Identified retinal ganglion cells were isolated from postnatal cat retinas and their dendrites were removed by trituration and centrifugation. The denuded cells were placed in a cell culture system and allowed to reexpress dendritic arbors in the absence of afferent input, target tissue, and interactions with neighboring ganglion cells. The retinal ganglion cells were grown above a feeder layer of astrocytes on glass coverslips equipped with paraffin pedestals. The spatial patterns of the reexpressed neurites were quantitatively analyzed using a number of measures, including an estimate of the Hausdorff dimension, H, which was used as a scale-independent metric for how well the neurite patterns filled in a restricted spatial domain. As assessed by the estimation of the Hausdorff dimensions, the neurites from a single cell achieve uniform coverage of a restricted territory independent of the total neurite length or the total number of inter-branch-point segments. A comparison with H values of ganglion cells from the intact retina revealed a similar trend. These results suggest that these cultured ganglion cells can express an intrinsic growth strategy for the uniform coverage of a restricted territory. The arbors expressed in the culture system displayed a limited range of diameters and exhibited morphology similar to the alpha-, beta-, and gamma-ganglion cells of the intact retina in the absence of afferent input or the influences of neighboring cells and target tissue. Time-lapse video data revealed that individual cultured cells showed extensive dendritic remodeling during their growth; however, after about 3 d in culture, this remodeling did not appreciably affect the territorial coverage of a cell. In the intact retina, the existence of dendritic sheets that independently and uniformly sample visual space may result from this intrinsic ability to elaborate dendrites that uniformly cover or fill in a restricted territory.

Animals↗
PubMed1976

Nature and origin of patterns of changes in cell shape in embryos.

Spatial patterns of the future elongation of cells exist in the early embryo. In the newt, such a pattern of changes of cell shape contributes to the formation of the neural plate. Regardless of where neural plate cells are transplanted, they change shape as prescribed by the pattern. Embryonic induction has a role in establishing this pattern.

Animals↗
PubMed1978

Spatial-frequency masking with briefly pulsed patterns.

Spatial-frequency masking was studied with briefly pulsed (25 ms) vertical gratings. The mask was a noise grating, and the test pattern was a sinusoidal grating. A low-frequency band of noise masked a low- but not high-spatial-frequency test grating when the patterns were presented simultaneously. A high-frequency band of noise did not mask a low-frequency test grating when the patterns were presented simultaneously or when the mask was presented after the test pattern (backward masking). Masking was, however, observed when the mask or test pattern was of sufficiently high contrast so that the stimuli had nonlinear distortion and thus produced DC shifts of the field luminance.

Humans↗
PubMed2026

Spatial clustering and transmission networks of multidrug-resistant tuberculosis in Rwanda: a national retrospective genomic and spatial epidemiological study.

BACKGROUND: Approximately 96% of rifampicin resistance/multidrug-resistant tuberculosis (RR/MDR-TB) cases in Rwanda result from direct transmission rather than acquired resistance. However, the nationwide spatial distribution and transmission dynamics of RR/MDR-TB remain poorly characterised. This study aims to analyse spatial patterns of RR/MDR-TB in Rwanda and explore relationships between spatial proximity and RR/MDR-TB strains' genetic relatedness. METHODS: We conducted a retrospective analysis of 249 confirmed RR-TB cases across Rwanda from 2017 to 2024, using the known geolocations of patients' residences. Spatial and space-time clustering was assessed using Kulldorff's scan statistics. Demographic and socioeconomic determinants were evaluated using multivariable regression. For 201 cases with whole-genome sequencing data, we performed transmission analysis using a 5-SNP threshold to define recent transmission clusters and investigated spatial relationships within genetically related strains. RESULTS: Significant spatial clustering of RR/MDR-TB was identified in 21 sectors, mainly in Nyarugenge, southern Gasabo and western Kicukiro (relative risk: 10.06; p<0.001). Our multivariable analysis showed that population density is positively associated with case notification rates. Molecular analysis revealed 88.5% of cases belonged to genotype clusters defined using a 12-SNP threshold, with 73.6% forming clusters at a strict 5-SNP threshold. Spatial K-function analysis of the six major clusters revealed heterogeneous transmission patterns, characterised by both tightly clustered outbreaks and regional transmission networks that spanned administrative boundaries. Most clusters (5/6) extended beyond Kigali, indicating that transmission networks operate across administrative divides. CONCLUSION: RR/MDR-TB in Rwanda shows significant spatial clustering with transmission occurring through both localised and regional networks. Integrating genomic and spatial data reveals transmission patterns that extend beyond household contacts and administrative boundaries. These findings underscore the need to implement geographically targeted interventions that address community-level transmission to control RR/MDR-TB in Rwanda effectively.

Rwanda↗
PubMed1992

Effect of pattern adaptation on spatial frequency discrimination.

The effect of pattern adaptation on spatial frequency discrimination was examined in two experiments. In the first experiment delta f/f was measured (with and without adaptation) as a function of stimulus contrast; in the second experiment the contrast required to discriminate a fixed delta f/f was measured (with and without adaptation) as a function of the value of delta f/f. Maximum precision, as measured by the asymptotic value that delta f/f approaches at medium and high contrasts, was not altered by adaptation. Rather, the effect of adaptation was to translate the functions relating delta f/f and contrast along the log-contrast axis, i.e., to increase by a constant factor the contrast required to achieve a given precision of discrimination. This factor agreed closely with the factor by which adaptation raised the contrast threshold for detection of the test stimuli. The largest effects were observed when the reference and the adapting stimuli had the same spatial frequency (5 cycles/deg). Smaller or negligible effects were observed when reference and adapting frequencies differed by an octave.

Adaptation, Ocular↗
PubMed1989

Component analysis of spatial and spectral patterns in multispectral images. II. Entropy minimization.

In Part I [J. Opt. Soc. Am. A 4, 2101 (1987)] of this series, we developed a method for estimating both spatial patterns and spectral curves of components in a multispectral scene. This method does not need spatial and spectral information about the components but only multispread imagery data. The estimation is given as a feasible solution set satisfying the nonnegativity constraint for density and spectral response for all components at all pixels. In this paper, we estimate unique solutions for both the component patterns and the spectra from the feasible solution set. The solution is given by optimizing an entropy minimization criterion. This criterion enhances the spectral or spatial features of individual components. Two experimental results are shown to demonstrate the effectiveness of this method with biological and cytochemical specimens. The limitations of this method for unique pattern estimation are also discussed.

Algorithms↗
PubMed1991

Spatial interactions in apparent contrast: inhibitory effects among grating patterns of different spatial frequencies, spatial positions and orientations.

Suppression of the apparent contrast of a small 4 cycle wide suprathreshold sine wave grating patch by a high contrast sine wave grating surround pattern was studied as a function of the spatial frequency, orientation and spatial extent of the surround. The data are consistent with the existence of a complex network of inhibitory interconnections among mechanisms that mediate contrast perception. These connections must extend over spatial distances equivalent to more than 12 cycles of the central grating patch.

Adaptation, Physiological↗
PubMed1988

Electrosensory maps form a substrate for the distributed and parallel control of behavioral responses in weakly electric fish.

Electroreceptors, distributed over the body surface of weakly electric fish, code the local amplitude and phase, or timing of zerocrossing, of the animal's electric signals. These signals are generated by rhythmic discharges of the electric organ and form a dipole-like field around the animal. This field is perturbed by interference with electric fields of other fish as well as by the appearance of objects electrically different from water. The spatial and temporal structure of such perturbations can be interpreted as the electric image of interfering fields and moving objects. This strategy of assessing the environment is called 'electrolocation', a form of 'seeing' with the body surface. Electric images are analyzed in somatotopically ordered strata of neurons within the central nervous system. Primary electrosensory afferents project to somatotopically ordered layers of higher-order neurons in the electrosensory lateral line lobe (ELL) of the hindbrain. Phase and amplitude information are processed in separate layers of the ELL. The phase of the signal in a given region of the body surface is coded by the timing of spikes of spherical cells marking the zerocrossings of the electric signal. This phase information is relayed to lamina 6 of the torus semicircularis of the midbrain. Rises and falls in local amplitude are coded by the activity of different pyramidal cell types, E- and I-units, which project to various laminae of the torus above and below lamina 6. The somatotopic organization of the torus allows for computations of spatial patterns in electrosensory information. Within lamina 6, differences in the phase of signals from different parts of the body surface are computed. Differential-phase information is then relayed to deeper laminae of the torus and remains in topographic register with amplitude information. This organization allows for joint evaluation of spatially related patterns of amplitude and phase modulations on the animal's body surface within local neuronal circuits of the torus. A topographic projection of the torus relays amplitude and differential-phase information to the optic tectum where a further joint evaluation of amplitude and phase serves to control behavioral responses. The control of a particular behavioral performance, the 'jamming avoidance response', is of a distributed nature in that the representations of individual sites on the body surface contribute cumulatively to shift the electric organ pacemaker frequency.(ABSTRACT TRUNCATED AT 400 WORDS)

Action Potentials↗
PubMed1987

Distribution of GABAergic neurons and axon terminals in the macaque striate cortex.

Antisera to glutamic acid decarboxylase (GAD) and gamma-aminobutyric acid (GABA) have been used to characterize the morphology and distribution of presumed GABAergic neurons and axon terminals within the macaque striate cortex. Despite some differences in the relative sensitivity of these antisera for detecting cell bodies and terminals, the overall patterns of labeling appear quite similar. GABAergic axon terminals are particularly prominent in zones known to receive the bulk of the projections from the lateral geniculate nucleus; laminae 4C, 4A, and the cytochrome-rich patches of lamina 3. In lamina 4A, GABAergic terminals are distributed in a honeycomb pattern which appears to match closely the spatial pattern of geniculate terminations in this region. Quantitative analysis of axon terminals that contain flat vesicles and form symmetric synaptic contacts (FS terminals) in lamina 4C beta and in lamina 5 suggest that the prominence of GAD and GABA axon terminal labeling in the geniculate recipient zones is due, at least in part, to the presence of larger GABAergic axon terminals in these regions. GABAergic cell bodies and their initial dendritic segments display morphological features characteristic of nonpyramidal neurons and are found in all layers of striate cortex. The density of GAD and GABA immunoreactive neurons is greatest in laminae 2-3A, 4A, and 4C beta. The distribution of GABAergic neurons within lamina 3 does not appear to be correlated with the patchy distribution of cytochrome oxidase in this region; i.e., there is no significant difference in the density of GAD and GABA immunoreactive neurons in cytochrome-rich and cytochrome-poor regions of lamina 3. Counts of labeled and unlabeled neurons indicate that GABA immunoreactive neurons make up at least 15% of the neurons in striate cortex. Layer 1 is distinct from the other cortical layers by virtue of its high percentage (77-81%) of GABAergic neurons. Among the other layers, the proportion of GABAergic neurons varies from roughly 20% in laminae 2-3A to 12% in laminae 5 and 6. Finally, there are conspicuous laminar differences in the size and dendritic arrangement of GAD and GABA immunoreactive neurons. Lamina 4C alpha and lamina 6 are distinguished from the other layers by the presence of populations of large GABAergic neurons, some of which have horizontally spreading dendritic processes. GABAergic neurons within the superficial layers are significantly smaller and the majority appear to have vertically oriented dendritic processes.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1983

Spatial and temporal patterns of deoxyribonucleic acid synthesis and mitosis in the endometrial stroma during decidualization in the pseudopregnant rat.

A quantitative study was made of the spatial patterns of stromal cell mitosis and DNA synthesis in the endometrium of the pseudopregnant rat before and during decidualization. A colchicine block was used for mitotic counts, and DNA synthesis was studied by [3H] thymidine autoradiography. Observations were also made on the subsequent fates of [3H] thymidine-labeled stromal cells. Before the onset of decidualization, on Days 3 and 4 (vaginal cornification = Day 0), mitosis was largely confined to the subepithelial stroma along the sides and around the antimesometrial pole of the lumen. [3H] thymidine labeling and stromal mitosis following a decidualizing stimulus at noon on Day 4 of pseudopregnancy were first seen close to the uterine lumen, with subsequent spread to deeper layers of the endometrium. At noon on Day 5, mitotic figures were numerous on all sides of the lumen and at all depths in the endometrium. At later stages, mitosis and the development of polyploidy continued in the decidual tissue, but little DNA synthesis or mitosis occurred in the basal zone of the stroma adjacent to the myometrium. In this zone, many cells in animals given [3H] thymidine 18 to 24 h after induction of decidualization remained heavily labeled throughout the growth and regression of deciduomata. Labeled cells derived from the basal zone and outer edge of the decidual capsule were present in the stroma of the regenerated endometrium following the regression of deciduomata. It was concluded that although cells at all depths in the endometrial stroma undergo DNA synthesis and mitosis in the early stages of response to a decidualizing stimulus, their subsequent behavior and fate depend upon their position in the endometrium.

Animals↗
PubMed1987

The dynamics of the cat retinal X cell centre.

1. The dynamics of the centre mechanism of individual cat X retinal ganglion cells is investigated. The visual stimuli consist of temporal contrast modulation of stationary patterns. In order to study the response of the centre mechanism, patterns were either sine gratings of high spatial frequency or small circular spots positioned over the receptive-field centre. 2. Responses to contrast reversal are approximately linear. However, as the modulation depth of the stimulus increases, responses become more transient. Ganglion cell responses show this phenomenon at moderate contrasts (e.g. 0.1), which do not elicit discharges that approach the maximum firing rate of the ganglion cell. 3. A sequence of dynamical models are constructed from responses elicited by sum-of-sinusoids modulation of the spatial pattern. The first model is strictly linear. It consists of a series of low-pass filters and a single high-pass filter. The linear model predicts the approximate shape of the step response, but does not account for the change in shape of the response as a function of modulation depth. 4. The second model, a quasi-linear model, allows the 'linear' dynamics to vary slowly with a neural measure of contrast. The main effect of high contrast is a shorter time constant in the high-pass filter. This model accounts qualitatively for the increased transience of the response, but fails to predict the magnitude of the effect at higher modulation depths. 5. In the third model, the transfer characteristics of the centre response adjust rapidly as contrast changes. This intrinsically non-linear model provides excellent agreement with observed response to steps and more complex modulation patterns. 6. The non-linearity necessitated by a voltage-to-spikes transduction is analysed quantitatively. In most ganglion cells, a simple truncation at 0 impulses/s (and no saturation) explains the changes in apparent gain and mean firing rate that occur as modulation depth is increased. A non-linear voltage-to-spike transduction per se cannot account for the observed effect of contrast on dynamics. 7. The parameters of the dynamical model are measured for a population of twenty-seven X ganglion cells (nineteen on-centre and eight off-centre). The low-pass stage and the strength of the high-pass stage are relatively uniform across the population. The over-all gain and the dynamics of the high-pass stage vary substantially across the population, but show no consistent dependence on the on-off distinction or on retinal location. Some implications of this variability for retinal function are discussed.

Action Potentials↗
PubMed2026

Pattern Formation in a Spatial Public Goods Dilemma due to Diffusive or Directed Motion.

The costly provision of public goods serves as a model problem for the evolution of cooperative behavior, presenting a social dilemma between the collective benefits of shared resources and the individual incentive to free-ride in resource production. The spatial structure of populations can also impact cooperation over public goods, as diffusion of public goods and intentional motion of individuals towards regions with greater resources can interact with population and public goods dynamics to produce heterogeneous patterns in the spatial distribution of strategies and resources. In this paper, we build off a model introduced by Young and Belmonte for the reaction dynamics of interacting individuals and an explicit public good, deriving a system of PDEs that describes the spatial profiles of strategies and the public good in the presence of both diffusive motion of individuals and resources and chemotaxis-like directed motion of individuals in response to gradients in the concentration of public goods. Through linear stability analysis, we show that spatial patterns in strategic and public goods profiles can emerge due to either Turing instability with high defector diffusivity or a directed-motion instability through strong sensitivity of cooperators towards increasing resource concentration. We further explore the emergent spatial patterns with a mix of weakly nonlinear stability analysis and numerical simulation, showing that, for a wide range of reaction parameters, diffusion-driven instability appears to increase cooperation and public goods across the spatial domain, while directed motion of cooperators towards public goods tends to decrease cooperation and environmental quality across the environment.

Models, Biological↗