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At least 667 records · Page 37Linked to original sources

PubMed1998

Event-related magnetic fields in the auditory cortex of man during unilateral movements: a discriminant function analysis.

It is often assumed that sensorimotor coordination is a feature of the sensorimotor areas of the neocortex only. The purpose of the present study was to examine how this phenomenon is reflected in the auditory cortex of man. Ten subjects were engaged in a stimulus-reaction paradigm, in which each of two acoustical tones was associated to either of two motor reactions. Magnetic fields recorded with a 122-channel magnetometer were modelled by current dipoles. The spatial coordinates as well as the amplitudes of the dipoles were analyzed from 90 to 110 ms after stimulus onset using discriminant analysis. The results suggest that the dipole trajectory in the auditory cortex of the right hemisphere and amplitudes of the dipoles in the auditory cortex of the left hemisphere already 90-110 ms after the beginning of the stimulus could be affected not only by physical features of the stimulus, but also by the motor task required as a reaction.

Acoustic Stimulation↗

PubMed1992

Racial and social correlates of age-related changes in functioning.

Six waves of observations spanning a decade on a panel of 566 Black and 5,196 non-Black survivors were utilized to examine social and racial differences in age-related changes in functioning. An index consisting of three dimensions was used to assess functioning: physical functioning, self-care capacity, and self-rated well-being. Growth curve analysis was used to assess variations in trajectories of functional impairment across Black/non-Black, poor/nonpoor, male/female, and high-school/non-high-school graduate subpanels. Trajectories vary across social groups in the expected manner. However, we note that the trajectories are not linear and that substantial variability exists within both the Black and non-Black subpanels. Moreover, we note that Blacks report poorer functional status than non-Blacks even with income and education controlled. However, age changes do not differ across Black and non-Black subpanels, as predicted by the multiple-jeopardy hypothesis.

Activities of Daily Living↗

PubMed2006

The effect of the loading condition corresponding to functional shoulder activities on trabecular architecture of glenoid.

There is little information on bone morphology as it relates to shoulder activities. This study investigated how loads corresponding to functional shoulder activities affect the trabecular architecture of the glenoid. Two different protocols were used. Protocol 1 investigated the material and morphological characteristics of the glenoid by analyzing digitized trabecular bone images obtained from 12 cadaver scapula specimens. Protocol 2 used a finite element analysis (FEA) to compute the principal stress trajectories acting within the glenoid. The principal stresses were derived for five loading conditions, which represent typical functional shoulder activities. The study showed that shoulder activity involved in carrying a light load makes the greatest contribution to the trabecular architecture compared with other shoulder activities considered in this study (p<0.05). With all of the activities considered in this study, the lateral region, particularly in the anterior and posterior portions, showed greater deviation and greater sensitivity to variation under loading conditions than did the other regions (p<0.05). These results suggest that owing to the extra sensitivity of the anterior and posterior parts of the lateral region, these regions may be more informative in the analysis of the trabecular architecture following shoulder musculoskeletal injuries. These results may provide essential design information for shoulder prostheses and contribute to an understanding of morphological changes resulting from injury.

Activities of Daily Living↗

PubMed2004

A model-based approach for automated in vitro cell tracking and chemotaxis analyses.

BACKGROUND: Chemotaxis may be studied in two main ways: 1) counting cells passing through an insert (e.g., using Boyden chambers), and 2) directly observing cell cultures (e.g., using Dunn chambers), both in response to stationary concentration gradients. This article promotes the use of Dunn chambers and in vitro cell-tracking, achieved by video microscopy coupled with automatic image analysis software, in order to extract quantitative and qualitative measurements characterizing the response of cells to a diffusible chemical agent. METHODS: Previously, we set up a videomicroscopy system coupled with image analysis software that was able to compute cell trajectories from in vitro cell cultures. In the present study, we are introducing a new software increasing the application field of this system to chemotaxis studies. This software is based on an adapted version of the active contour methodology, enabling each cell to be efficiently tracked for hours and resulting in detailed descriptions of individual cell trajectories. The major advantages of this method come from an improved robustness with respect to variability in cell morphologies between different cell lines and dynamical changes in cell shape during cell migration. Moreover, the software includes a very small number of parameters which do not require overly sensitive tuning. Finally, the running time of the software is very short, allowing improved possibilities in acquisition frequency and, consequently, improved descriptions of complex cell trajectories, i.e. trajectories including cell division and cell crossing. RESULTS: We validated this software on several artificial and real cell culture experiments in Dunn chambers also including comparisons with manual (human-controlled) analyses. CONCLUSIONS: We developed new software and data analysis tools for automated cell tracking which enable cell chemotaxis to be efficiently analyzed.

Cell Culture Techniques↗

PubMed1999

Computational analysis of chain flexibility and fluctuations in Rhizomucor miehei lipase.

We have performed molecular dynamics simulation of Rhizomucor miehei lipase (Rml) with explicit water molecules present. The simulation was carried out in periodic boundary conditions and conducted for 1. 2 ns in order to determine the concerted protein dynamics and to examine how well the essential motions are preserved along the trajectory. Protein motions are extracted by means of the essential dynamics analysis method for different lengths of the trajectory. Motions described by eigenvector 1 converge after approximately 200 ps and only small changes are observed with increasing simulation time. Protein dynamics along eigenvectors with larger indices, however, change with simulation time and generally, with increasing eigenvector index, longer simulation times are required for observing similar protein motions (along a particular eigenvector). Several regions in the protein show relatively large fluctuations and in particular motions in the active site lid and the segments Thr57-Asn63 and the active site hinge region Pro101-Gly104 are seen along several eigenvectors. These motions are generally associated with glycine residues, while no direct correlations are observed between these fluctuations and the positioning of prolines in the protein structure. The partial opening/closing of the lid is an example of induced fit mechanisms seen in other enzymes and could be a general mechanism for the activation of Rml.

Amino Acid Sequence↗

PubMed1998

Locally accessible conformations of proteins: multiple molecular dynamics simulations of crambin.

Multiple molecular dynamics (MD) simulations of crambin with different initial atomic velocities are used to sample conformations in the vicinity of the native structure. Individual trajectories of length up to 5 ns sample only a fraction of the conformational distribution generated by ten independent 120 ps trajectories at 300 K. The backbone atom conformational space distribution is analyzed using principal components analysis (PCA). Four different major conformational regions are found. In general, a trajectory samples only one region and few transitions between the regions are observed. Consequently, the averages of structural and dynamic properties over the ten trajectories differ significantly from those obtained from individual trajectories. The nature of the conformational sampling has important consequences for the utilization of MD simulations for a wide range of problems, such as comparisons with X-ray or NMR data. The overall average structure is significantly closer to the X-ray structure than any of the individual trajectory average structures. The high frequency (less than 10 ps) atomic fluctuations from the ten trajectories tend to be similar, but the lower frequency (100 ps) motions are different. To improve conformational sampling in molecular dynamics simulations of proteins, as in nucleic acids, multiple trajectories with different initial conditions should be used rather than a single long trajectory.

Computer Simulation↗

PubMed1998

Molecular dynamics and continuum solvent studies of the stability of polyG-polyC and polyA-polyT DNA duplexes in solution.

Molecular dynamics simulation in explicit solvent and continuum solvent models are applied to investigate the relative stability of A- and B-form helices for two DNA sequences, dA10-dT10 and dG10-dC10 in three structural forms. One structural form is based on an unrestrained molecular dynamics (MD) trajectory starting from a canonical B-DNA structure, the second is based on a MD trajectory starting in a canonical B-DNA structure with the sugars constrained to be C2'-endo and the third simulation started from a canonical A-DNA structure with the sugars constrained to C3'-endo puckers. For the energetic analysis, structures were taken as snapshots from nanosecond length molecular dynamics simulations computed in a consistent fashion in explicit solvent, applying the particle mesh Ewald method and the Cornell et al. force field. The electrostatic contributions to solvation free energies are computed using both a finite-difference Poisson-Boltzmann model and a pairwise Generalized Born model. The non-electrostatic contributions to the solvation free energies are estimated with a solvent accessible surface area dependent term. To estimate the gas phase component of the relative free energy between the various structures, the mean solute internal energies (determined with the Cornell et al. molecular mechanics potential including all pairwise interactions within the solute) and estimates of the solute entropy (using a harmonic approximation) were used. Consistent with experiment, the polyG-polyC (GC) structures are found to be much more A-phillic than the polyA-polyT (AT) structures, the latter being quite A-phobic. The dominant energy components responsible for this difference comes from the internal and van der Waal energies. A perhaps less appreciated difference between the GC and AT rich sequences is suggested by the calculated salt dependence which demonstrates a significantly enhanced ability to drive GC rich sequences towards an A-form structure compared to AT rich sequences. In addition to being A-phobic, the AT structure also has a noticably larger helical repeat than GC and other mixed sequence duplexes, consistent with experiment. Analysis of the average solvent density from the trajectories shows hydration patterns in qualitative agreement with experiment and previous theoretical treatments.

Computer Simulation↗

PubMed2005

Static and dynamic descriptions of bond breaking/formation: a complementary view?

Ab initio molecular-dynamic simulations using density-functional theory and the recent atom-centered density-matrix propagation (ADMP) method were used to study the bond breaking and formation for a case-study substitution nucleophilic bimolecular reaction, namely, the Walden inversion. Using the atoms-in-molecule approach, we have performed a detailed analysis to investigate intra- and intermolecular charge transfer along the ADMP trajectory. These results were compared to those obtained considering a static approach, such as the intrinsic reaction path. In particular, the topological properties computed along the dynamic trajectory well evidence a stronger electron exchange tending to spontaneously maximize the rising covalent interaction. Furthermore, their analysis suggests that the bond formation mechanism involves a reactive intermediate with a bonding interaction stronger than in the final product.

Journal Article↗

PubMed2000

Shock wave profiles in the burnett approximation

This paper is devoted to a discussion of the profiles of shock waves using the full nonlinear Burnett equations of hydrodynamics as they appear from the Chapman-Enskog solution to the Boltzmann equation. The system considered is a dilute gas composed of rigid spheres. The numerical analysis is carried out by transforming the hydrodynamic equations into a set of four first-order equations in four dimensions. We compare the numerical solutions of the Burnett equations, obtained using Adam's method, with the well known direct simulation Monte Carlo method for different Mach numbers. An exhaustive mathematical analysis of the results offered here has been done mainly in connection with the existence of heteroclinic trajectories between the two stationary points located upflow and downflow. The main result of this study is that such a trajectory exists for the Burnett equations for Mach numbers greater than 1. Our numerical calculations suggest that heteroclinic trajectories exist up to a critical Mach number ( approximately 2.69) where local mathematical analysis and numerical computations reveal a saddle-node-Hopf bifurcation. This upper limit for the existence of heteroclinic trajectories deserves further clarification.

Journal Article↗

PubMedDate not supplied

Cigarette smoking from adolescence to young adulthood: women's developmental trajectories and associates outcomes.

OBJECTIVES: This study aimed to compare 1,442 women with distinct developmental trajectories of smoking from ages 13-23 on important young adult outcomes at age 29 (e.g., education, income, mental and physical health, arrest history, drug and alcohol abuse), as well as early transitions to sexual intercourse, parenthood, and marriage. METHODS: Women were classified as Abstainers or into 1 of 5 trajectory classes for which they had the highest probability of membership: Stable Highs, Early Increasers, Late Increasers, Triers, and Decreasers. Regression analysis was used to model outcomes as a function of trajectory class membership. RESULTS: Abstainers and Triers generally had more favorable outcomes than Stable Highs and Early Increasers. Decreasers were more likely to graduate from college than Stable Highs and Early Increasers and had a lower arrest rate than Stable Highs. Women who increased their smoking from initial low levels (Late Increasers) generally had poorer young adult outcomes compared to Triers and Abstainers, but lower risk for early sex and early parenthood compared to Stable Highs and Early Increasers. CONCLUSIONS: Women with certain patterns of smoking from age 13-23 are at heightened risk for early transitions to sexual activity and parenthood, as well as health, behavioral, and socioeconomic problems during young adulthood.

Adolescent↗

PubMed1995

Harmonicity and anharmonicity in protein dynamics: a normal mode analysis and principal component analysis.

A comparison of a normal mode analysis and principal component analysis of a 200-ps molecular dynamics trajectory of bovine pancreatic trypsin inhibitor in vacuum has been made in order to further elucidate the harmonic and anharmonic aspects in the dynamics of proteins. An anharmonicity factor is defined which measures the degree of anharmonicity in the modes, be they principal modes or normal modes, and it is shown that the principal mode system naturally divides into anharmonic modes with peak frequencies below 80 cm-1, and harmonic modes with frequencies above this value. In general the larger the mean-square fluctuation of a principal mode, the greater the degree of anharmonicity in its motion. The anharmonic modes represent only 12% of the total number of variables, but account for 98% of the total mean-square fluctuation. The transitional nature of the anharmonic motion is demonstrated. The results strongly suggest that in a large subspace, the free energy surface, as probed by the simulation, is approximated by a multi-dimensional parabola which is just a rescaled version of the parabola corresponding to the harmonic approximation to the conformational energy surface at a single minimum. After 200 ps, the rescaling factor, termed the "normal mode rescaling factor," has apparently converged to a value whereby the mean-square fluctuation within the subspace is about twice that predicted by the normal mode analysis.

Animals↗

PubMed2004

Autonomously oscillating biochemical systems: parametric sensitivity of extrema and period.

This work addresses sensitivity analysis of autonomously oscillating biochemical systems. Building on results from the engineering literature, a general analysis is presented which addresses key features of oscillatory trajectories, namely the period and local maximum or minimum values of species concentrations and reaction rates. A discussion of sensitivity invariants generalises results from steady-state sensitivity analysis to this context. The results are illustrated by the application to a model of a circadian oscillator.

Biochemistry↗

PubMed1988

Structure-function relationships in the primate superior colliculus. I. Morphological classification of efferent neurons.

1. Neurons in the superior colliculus (SC) of anesthetized paralyzed squirrel monkeys were injected intracellularly with horseradish peroxidase (HRP) to establish a morphological classification of tectal efferent neurons in this species. These neurons were physiologically identified by their antidromic responses following stimulation of the contralateral predorsal bundle or SC. These cells also responded with postsynaptic potentials to stimulation of the ipsilateral substantia nigra and cerebral peduncle and the contralateral tectum. 2. Quantitative light microscopic analysis of the somatodendritic profiles and axonal trajectories of 27 recovered cells revealed the existence of three major groups of tectal efferent neurons: L (n = 7), X (n = 8), and T (n = 12). 3. L neurons are small or medium size cells with relatively elaborate dendritic trees and are located mainly in the superficial layers of the SC. They participate in the ipsilateral descending and dorsal ascending tectofugal bundles. Intrinsic collaterals of L axons deploy a large number of boutons both near the parent cell body and more ventrally within the deeper tectal layers. 4. X neurons are mostly large in size and multipolar in shape with relatively complex dendritic trees. Their cell bodies are situated mainly in the stratum griseum intermedium and occasionally in the stratum opticum. Axons of X neurons participate in the crossed descending and ipsilateral ventral ascending projections of the SC. In addition, the axonal system of about half of the X neurons includes recurrent collaterals. 5. T neurons are located mainly in the ventral stratum opticum and the dorsal stratum griseum intermedium. They have small or medium-sized, trapezoid or ovoid cell bodies and relatively simple radiating or vertical dendritic trees. Their axons usually participate in two of the major tectofugal bundles besides providing a commissural component and recurrent collaterals. 6. Morphological details revealed in the present study support the notion that distinct tectofugal axonal systems originate from efferent neurons of the primate SC that differ both as to their location in the tectum as well as the appearance of their somata and dendritic trees. The resulting morphological classification of tectal efferent cells provides a framework for the analysis of tectal function in terms of populations of identified neurons.

Animals↗

PubMed2005

Kinematical measure for spastic reaching in children with cerebral palsy.

BACKGROUND: Practitioners need more sensitive measure to quantify reaching movement for judgment of the treatment effects and reflecting the degrees of motor impairment in upper extremities. The purposes of this study were to identify the specific kinematic characteristics between normal and spastic reaching under different levels of accuracy, and to determine the most sensitive kinematic variable for quantifying the interference of spasticity on reaching. METHODS: Ten normal subjects as control group and ten subjects with spastic cerebral palsy as experimental group were studied. Participants were asked to reach, at a self-selected pace, toward two different sizes of buttons (one with accuracy constraint and the other with non-accuracy constraint) away from normalized distance. Motion analysis system was used to record the trajectory of reaching performance. Kinematic variables of reaching movement were computed and analyzed. FINDINGS: Measure for movement smoothness presented larger effect size (0.24-0.43) than other kinematic variables adopted in this study. Under high-accuracy reaching, children with spastic cerebral palsy had a prolonged movement time than normal children (P<0.05). Modified Ashworth score was significantly correlated to normalized jerk score, number of movement unit and movement time (r=0.56-0.75). Number of movement unit was the most sensitive kinematic variable to discriminate between normal and spastic reaching. INTERPRETATION: Development of reliable, valid, and sensitive multi-joint biomechanical evaluation is required, particularly for natural and goal-oriented reaching movement. It is concluded that measure of movement smoothness may be applied as valid and sensitive index to quantify the level of coordinative motor performance for subjects with spastic movement disorder.

Adolescent↗

PubMed1999

Automatic synthesis of synergies for control of reaching--hierarchical clustering.

In this paper we describe a novel method for determining synergies between joint motions in reaching movements by hierarchical clustering. A set of recorded elbow and shoulder trajectories is used in a learning algorithm to determine the relationships between angular velocities at elbow and shoulder joints. The learning algorithm is based on optimal criteria for obtaining the hierarchy of descriptions of movement trajectories. We show that this method finds complex synergism between optimal joint trajectories for a given set of data and angular velocities at the shoulder and elbow joints. Three other machine learning techniques (ML) are used for comparison with our method of hierarchical clustering of trajectories. These MLs are: (1) radial basis functions (RBF), (2) inductive learning (IL), and (3) adaptive-network-based fuzzy inference system (ANFIS). Better error characteristics were obtained using the method of hierarchical clustering in comparison with the other techniques. The advantage of the method of hierarchical clustering with respect to the other MLs is in integrating the spatial and temporal elements of reaching movements. Determination and analysis of spatio-temporal events of movement trajectories is a useful tool in designing control systems for functional electrical stimulation (FES) assisted manipulation.

Algorithms↗

PubMed1993

Measuring the similarity between trajectories using clustering techniques.

A clustering method has been developed to group signals that display similar dynamic behavior. The procedure involves using the method of time delay embedding to construct a trajectory in state space from a time series. Certain features that characterize the geometry of the trajectory have been defined. These features were subjected to a series of statistical tests to determine their usefulness in a hierarchical clustering analysis. The latter is aimed at finding groups of similar trajectories. The trajectory-based clustering algorithm has been applied to simulated data, which included both stochastic data generated by a linear AR model, and nonlinear data generated by a Duffing oscillator. The results show that the algorithm works reliably in both cases.

Journal Article↗

PubMedDate not supplied

Comparison of head- and body-velocity trajectories during locomotion among healthy and vestibulopathic subjects.

The optimal strategies for improving locomotor stability in people with vestibulopathy remain unclear. To help identify likely targets for intervention, we sought to determine whether vestibulopathic postural control impairment during locomotor activity was more localized to either the head or the whole body. We used high curvature analysis (HCA) to quantify the smoothness of head- and body-velocity trajectories during repeated stepping in 18 vestibulopathic and 17 healthy subjects. We employed a mixed-model repeated measures analysis of variance to compare differences in head- and body-trajectory HCA scores. Pearson coefficients were used to describe relationships between head- and body-trajectory HCA scores within each group. The results revealed that neither head- nor body-velocity trajectories were relatively more impaired in subjects with vestibulopathy. Importantly, however, the smoothness of head and body trajectories was more strongly related in subjects with vestibulopathy compared with healthy subjects, suggesting that the fundamental motor control impairment produced by vestibulopathy may be related to an abnormal coupling of head and body motion. We discuss implications for locomotor training in patients with vestibulopathy.

Adult↗

PubMed2005

The relationship between seriously considering, planning, and attempting suicide in the youth risk behavior survey.

The assumed ordinal relationship between seriously considering, planning, and attempting suicide in the 1999 Youth Risk Behavior Survey was examined by constructing a trajectory that identified all possible response patterns among the four questions measuring suicidal activity. Statistical analysis tested for differences in frequency of risk behaviors across levels of the trajectory. Overall, the trajectory provided insight to the progression of adolescent suicidal activity and demonstrated usefulness as a measure of suicidal intent. Significant differences between means of dependent variables at each level of the normative trajectory supported the hypothesis that frequency of risk behaviors increases monotonically with successive suicidal thought and behavior.

Adolescent↗