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PubMed1983

Modification of trajectory of a pointing movement in response to a change in target location.

1. Arm movements toward a target involving motion at the shoulder and elbow joints and restricted to the sagittal plane were investigated. During some movements, target location changed suddenly, thus requiring an intentional correction of the trajectory by the human subject. 2. The reaction time to correct the trajectory was comparable to the reaction time to initiate the movement. 3. Coordination of arm and shoulder movements in this task was achieved by means of a reduction of the number of degrees of freedom of the movement. Such a simplification of the task took two forms. 4. Angular acceleration at the elbow and shoulder were linearly related to each other in the deceleratory phase of the movement, when the trajectory had to be corrected as well as when no such correction was required. 5. When the correction required an increase or decrease in flexor torque at the shoulder and elbow, electromyographic (EMG) activity in anterior deltoid and biceps increased or decreased simultaneously. When the correction demanded more activity in triceps and deltoid, these muscles were activated sequentially instead. It is concluded that rapid corrections of a movement involve the production of stereotyped patterns of activity in shoulder and elbow muscles.

Adult↗
PubMed1997

Preferential representation of instructed target location versus limb trajectory in dorsal premotor area.

The dorsal premotor area (PMd) of monkeys has been implicated in processes relating to movement preparation and movement selection. In the present study, we sought to determine whether PMd neurons that are activated during a delayed reaching task have directional responses that reflect either the target (i.e., the goal) of an intended movement or the physical properties of the movement itself. Two macaque monkeys were trained to perform a visually instructed, delayed reaching task with indirect visual feedback. The subjects and methods were identical to those described in the preceding paper. In the behavioral task, each subject moved a two-dimensional joystick with the right forelimb to align a cursor with targets presented on a video display. The paradigm dissociated the direction of forelimb movement from the spatial location of the target. This was accomplished by varying the spatial mappings between joystick and cursor. A variable delay separated the visual stimulus that instructed the target location (IS) from the visual stimulus that triggered the instructed movement (TS). Task-related activity was recorded from a total of 181 PMd neurons. The focus of this study was on directionally tuned neuronal responses that included 1) stimulus-related activity (phasic, following IS); 2) set-related activity (phasic, following IS and TS); and 3) movement-related activity (phasic, following TS). Of the entire sample of PMd neurons with directionally tuned activity, 114 were tested with two joystick/cursor mappings, permitting dissociation of directional responses that depended on limb trajectory from those that depended on target location. Task-related neuronal activity was classified as target-dependent if it covaried exclusively with target location across both conditions, and as limb-dependent if it covaried exclusively with limb trajectory. Directional activity that changed significantly across rotation conditions was classified as complex. Approximately one half of the sample of PMd neurons showed stimulus-related activity that was directionally tuned (56%, 64 of 114). Nearly all of the directionally classifiable stimulus-related activity was target dependent (94%, 44 of 47 responses), and none was limb dependent. A small proportion was classified as complex (6%, 3 of 47 responses). More than two thirds of the PMd neurons showed set-related activity that was directionally tuned (69%, 79 of 114). Among cells with set-related activity that was directionally classifiable, there were approximately 9 times as many target-dependent responses (76%, 48 of 63) as there were limb-dependent responses (8%, 5 of 63), with the remainder being complex (16%, 10 of 63). Approximately three quarters of the sample of PMd neurons showed early movement-related activity (before movement onset) that was directionally tuned (78%, 89 of 114). Among those cells whose early movement-related activity was directionally classifiable, there were > 3 times as many target-dependent responses ((51%, 34 of 66) as limb-dependent responses (14%, 9 of 66), with the remainder being complex (35%, 23 of 66). Approximately two thirds of the sample showed late movement-related responses (after movement onset) that were directionally tuned (68%, 78 of 114). Among those cells whose late movement-related activity was directionally classifiable, there were comparable numbers of target-dependent (25%, 15 of 61) and limb-dependent responses (28%, 17 of 61), with the remainder being complex (47%, 29 of 61). These results indicate a preferential representation of target location rather than limb trajectory among PMd neurons. Over the extended interval from IS to motor response, there was a gradual decline in the frequency of target-dependent activity and corresponding increases in the frequencies of both limb-dependent and complex activity. These findings suggest that PMd neurons may participate in mediating the sensory-to-motor transformation required by the delayed reaching

Animals↗
PubMed1993

Trajectory angle in stereotactic thalamotomy.

Most neurosurgeons use a frontal burr hole in stereotactic thalamotomy for movement disorders. However, the reports on this operation show a variation in trajectory with reference to the angles to the intercommissural line and the midsagittal plane. We studied the effect of the trajectory angles on operative results in 22 patients who underwent stereotactic thalamotomy for tremor control. The angle varied between 28 and 71 degrees (mean 44 +/- 10) in the sagittal plane, and between 0 and 25 (mean 11 +/- 7) in the coronal plane. There was linear correlation between the angles and the distances of a burr hole from the coronal suture and the midline. However, the angles did not show any correlation with the number of target corrections required, the size of the lesions made, tremor control and the incidence of complications. These findings indicate that the trajectory angle does not play an important role in stereotactic thalamotomy.

Adolescent↗
PubMed1984

Independence of myocardial oxygen consumption from pressure-volume trajectory during diastole in canine left ventricle.

We have found that myocardial oxygen consumption is linearly correlated with the systolic pressure-volume area in the canine left ventricle. This pressure-volume area is a specific area in the pressure-volume diagram that is circumscribed by the end-systolic pressure-volume relation line, the end-diastolic pressure-volume relation curve, and the systolic segment of the pressure-volume trajectory. This area is equivalent to the total mechanical energy generated by ventricular contraction, consisting of the external mechanical work and the mechanical potential energy. In the present study, we specifically changed the course of the diastolic segment of the pressure-volume trajectory without changing the systolic segment of the pressure-volume trajectory and the systolic pressure-volume area. Although the fractions of external mechanical work and mechanical potential energy in the pressure-volume area were markedly changed, the simultaneously measured left ventricular oxygen consumption remained unchanged. This result indicates that the myocardial oxygen consumption is predominantly determined by the total mechanical energy generated during systole, or the systolic pressure-volume area, independent of how the total mechanical energy is converted effectively to external mechanical work during the cardiac cycle.

Animals↗
PubMed2002

Socioeconomic trajectories and incident hypertension in a biracial cohort of young adults.

We assessed the impact of initial socioeconomic status and change in socioeconomic status across 10 years, ie, status trajectories, on the development of essential hypertension among black and white young men and women. Three thousand eight hundred twenty-seven normotensive individuals ages 18 to 30 years at study entry were followed for 10 years, with blood pressure, body mass index, and socioeconomic status characteristics measured at years 0, 2, 5, 7, and 10. Socioeconomic status trajectory measures were a new educational degree earned by year 10; difficulties paying for basics during years 2 to 10; and change in income category from year 5 to 10, defined in relation to year 0 status. Hypertension was defined as systolic blood pressure > or =140, diastolic blood pressure > or =90, or antihypertensive medication use at year 10. Reporting difficulties paying for basics at study entry (odds ratio=1.45, 95% confidence interval, 1.05 to 2.02) and continued difficulties during year 2 to 10 follow-up (odds ratio=1.62, 95% confidence interval, 1.04 to 2.53) were independently associated with incident hypertension, adjusted for race-gender group, body mass index, site, age, and initial systolic blood pressure. Decline in income from year 5 to 10 tended to be associated with hypertension, P=0.07, but a new educational degree after study onset was not. Socioeconomic trajectories are independently associated with incidence of hypertension. A dynamic index of socioeconomic status may be a useful concept in understanding the effects of socioeconomic status on the natural history of hypertension.

Adolescent↗
PubMed2006

Stereomotion suppression and the perception of speed: accuracy and precision as a function of 3D trajectory.

The precision and accuracy of speed discrimination performance for stereomotion stimuli were assessed for several receding 3D trajectories confined to the horizontal meridian. It has previously been demonstrated in a variety of tasks that detection thresholds are substantially higher when subjects observe a stereomotion stimulus than when simply viewing one of its component monocular half-images--a phenomenon known as stereomotion suppression (C. W. Tyler, 1971). Using monocularly visible motion in depth targets, we found mean speed discrimination thresholds to be higher for stereomotion, compared with monocular lateral speed discrimination thresholds for equivalent stimuli, demonstrating a disadvantage for binocular viewing in the case of speed discrimination as well. Furthermore, speed discrimination thresholds for motion in depth were not systematically affected by trajectory angle; hence, the disadvantage of binocular viewing persists even when there are concurrent changes in binocular visual direction. Lastly, there was a tendency for oblique trajectories of stereomotion to be perceived as faster than equally rapid motion receding directly away from the subject along the midline. Our data, in addition to earlier stereomotion suppression observations, are consistent with a stereomotion system that takes a noisy, weighted difference of the stimulus velocities in the two eyes to compute motion in depth.

Depth Perception↗
PubMed2002

Developmental trajectories, transitions, and nonlinear dynamical systems: a model of crime deceleration and desistance.

Research on crime-related developmental trajectories is reviewed with outcomes revealing the existence of several trajectories rather than a single general pattern. Each trajectory is marked by transitions that define the pattern's path and direction over time. These anticipated transitions differ from the unanticipated transitions known to precipitate crime deceleration and desistance. Borrowing principles from nonlinear dynamical systems theory--sensitive dependence on initial conditions, chaotic attractors, and self-organization in particular--this article offers a model of crime deceleration and desistance in which belief systems congruent with crime are altered in phases--initiation, transition, maintenance--to create belief systems incongruent with crime. The practical implications of this model are discussed and suggestions for future research are outlined.

Adolescent↗
PubMed2004

Density-independent population projection trajectories of chromosome-substituted lines resistant and susceptible to organophosphate insecticides in Drosophila melanogaster.

BACKGROUND: Seasonal fluctuations in susceptibility to organophosphate insecticides were observed in the Katsunuma population of Drosophila melanogaster for two consecutive years; susceptibility to three organophosphates tended to increase in the fall. To examine the hypothesis that variation in fitness among resistant and susceptible genotypes could trigger the change of genetic constitution within the fall population, we investigated density-independent population projection trajectories starting from single adult females with characteristics of chromosome-substituted lines resistant and susceptible to the three organophosphates. RESULTS: Density-independent population projection trajectories, expressed as the ratios of the number of each chromosome-substituted line to that of line SSS, for which all chromosomes were derived from the susceptible line, showed significant declines in numbers with time for all the resistant chromosome-substituted lines. CONCLUSION: The declining tendency in the density-independent population projection trajectories of the resistant chromosome-substituted lines could explain the simultaneous decline in the levels of resistance to the three organophosphates, observed in the Katsunuma population in the fall.

Age Factors↗
PubMed2004

Growth trajectory evident at birth affects age of first delivery in female monkeys.

Growth trajectories established early in life have proven to be important determinants of metabolism, health in adulthood, and ultimate mortality. The age of sexual maturation may also be set early in development, perhaps etched in utero. The following study used growth curve modeling to investigate the degree to which birth weight and weight gain before sexual maturation constrained the timing of reproduction in 147 female rhesus monkeys living under standardized social and nutritional conditions. Although size at birth by itself did not determine age of reproductive maturation, it was strongly associated with the subsequent developmental growth trajectory, which in turn predicted age at first offspring. In contrast to human studies indicating that small birth size is followed by a postnatal "catch-up" growth phase that accelerates menarche, growth trajectories remained distinctive in small and large infant monkeys. Thus, it was the sustained and stable disparity in size already evident at birth and amplified through development that accounted for variation in the age of adult sexual maturity.

Age Factors↗
PubMed2001

Effects of cumulative prenatal substance exposure and environmental risks on children's developmental trajectories.

Examined the effects of cumulative prenatal substance exposure and cumulative environmental risk on the developmental trajectories of 278 infants, toddlers, and preschool children. Results indicated that both cumulative risk indexes were significantly correlated. Results also indicated that both indexes were related to decrements in developmental trajectories (intercept and slope) from 3 to 57 months of age. Both prenatal exposure and environmental risk added unique variance to the prediction of developmental level and rate of growth when entered after covariates (i.e., birth weight and sex). However, across a number of models with and without covariates, environmental risk accounted for more variance in developmental trajectories than did prenatal exposure. Implications are discussed.

Age Factors↗
PubMed1997

The effects of length trajectory on the mechanical power output of mouse skeletal muscles.

The effects of length trajectory on the mechanical power output of mouse soleus and extensor digitorum longus (EDL) muscles were investigated using the work loop technique in vitro at 37 degrees C. Muscles were subjected to sinusoidal and sawtooth cycles of lengthening and shortening; for the sawtooth cycles, the proportion of the cycle spent shortening was varied. For each cycle frequency examined, the timing and duration of stimulation and the strain amplitude were optimized to yield the maximum power output. During sawtooth length trajectories, power increased as the proportion of the cycle spent shortening increased. The increase in power was attributable to more complete activation of the muscle due to the longer stimulation duration, to a more rapid rise in force resulting from increased stretch velocity and to an increase in the optimal strain amplitude. The power produced during symmetrical sawtooth cycles was 5-10 % higher than during sinusoidal work loops. Maximum power outputs of 92 W kg-1 (soleus) and 247 W kg-1 (EDL) were obtained by manipulating the length trajectory. For each muscle, this was approximately 70 % of the maximum power output estimated from the isotonic force-velocity relationship. We have found a number of examples suggesting that animals exploit prolonging the shortening phase during activities requiring a high power output, such as flying, jet-propulsion swimming and vocalization. In an evolutionary context, increasing the relative shortening duration provides an alternative to increasing the maximum shortening velocity (Vmax) as a way to increase power output.

Animals↗
PubMed1999

How muscles deal with real-world loads: the influence of length trajectory on muscle performance.

The performance of skeletal muscles in vivo is determined by the feedback received when the muscle interacts with the external environment via various morphological structures. This interaction between the muscle and the 'real-world load' forces us to reconsider how muscles are adapted to suit their in vivo function. We must consider the co-evolution of the muscles and the morphological structures that 'create' the load in concert with the properties of the external environment. This complex set of interactions may limit muscle performance acutely and may also constrain the evolution of morphology and physiology. The performance of skeletal muscle is determined by the length trajectory during movement and the pattern of stimulation. Important features of the length trajectory include its amplitude, frequency, starting length and shape (velocity profile). Many of these parameters interact. For example, changing the velocity profile during shortening may change the optimum values of the other parameters. The length trajectory that maximizes performance depends on the task to be performed. During cyclical work, muscles benefit from using asymmetric cycles with longer shortening than lengthening phases. Modifying this 'sawtooth' cycle by increasing the velocity during shortening may further increase power by augmenting force output and speeding deactivation. In contrast, when accelerating an inertial load, as in jumping, the predicted 'optimal' velocity profile has two peak values, one early and one late in shortening. During level running at constant speed, muscles perform tasks other than producing work and power. Producing force to support the body weight is performed with nearly isometric contractions in some of the limb muscles of vertebrates. Muscles also play a key role in producing stability during running, and the intrinsic properties of the musculoskeletal system may be particularly important in stabilizing rapid running. Recently, muscles in running invertebrates and vertebrates have been described that routinely absorb large amounts of work during running. These muscles are hypothesized to play a key role in stability.

Animals↗
PubMed2006

Differential geometry of normalized Stokes vector trajectories in anisotropic media.

Trajectory of the normalized Stokes vector on the Poincaré sphere corresponding to light propagation in anisotropic tissues with birefringence and biattenuance is derived. Analytic expressions are determined from the Serret-Frenet formulas and derivatives of arc length for five quantities including the tangent, normal, and binormal vectors with curvature and torsion. Depth variation of curvature and torsion of normalized Stokes vector trajectories corresponding to light propagating in rodent tail tendon are given. Use of analytic expressions for depth variation of curvature and torsion of the normalized Stokes vector trajectories on the Poincaré sphere is discussed for analysis of polarization-sensitive optical coherence tomography data recorded from anisotropic biological tissues with birefringence and biattenuance.

Algorithms↗
PubMed2006

Ensemble-based convergence analysis of biomolecular trajectories.

Assessing the convergence of a biomolecular simulation is an essential part of any careful computational investigation, because many fundamental aspects of molecular behavior depend on the relative populations of different conformers. Here we present a physically intuitive method to self-consistently assess the convergence of trajectories generated by molecular dynamics and related methods. Our approach reports directly and systematically on the structural diversity of a simulation trajectory. Straightforward clustering and classification steps are the key ingredients, allowing the approach to be trivially applied to systems of any size. Our initial study on met-enkephalin strongly suggests that even fairly long trajectories (approximately 50 ns) may not be converged for this small--but highly flexible--system.

Biopolymers↗
PubMed2002

Religious trajectories and transitions over the life course.

This study examined patterns of change and stability in religiosity over the life course. Open-ended interviews with 129 adults aged 65 and older provided a rich source of data for applying a life course perspective to the study of religion. Two theoretical constructs from the life course perspective (i.e., trajectories and transitions) were used as a framework for understanding religion and aging. The interviews were content analyzed to identify: 1) dimensions of religiosity that exhibit change; 2) patterns of religious trajectories; and 3) social forces that promote changes in religiosity. These analyses revealed four distinct patterns: stable, increasing, decreasing, and curvilinear trajectories. Several forces were involved with either increasing religiosity (e.g., child rearing, adverse life experiences) or decreasing religiosity (e.g., disillusionment with church members, adverse life experiences). Directions for future research are discussed.

Age Factors↗
PubMed2006

Outcomes in patients undergoing single-trajectory endoscopic third ventriculostomy and endoscopic biopsy for midline tumors presenting with obstructive hydrocephalus.

OBJECT: The primary aim of this study was to evaluate the success of endoscopic third ventriculostomy (ETV) as a treatment for obstructive hydrocephalus secondary to midline tumors (midbrain, pontine, pineal, tectal plate, thalamic, and third ventricular regions). In addition, the study examined the role and value of endoscopic tumor biopsy (ETB) in the management of such cases. All surgical procedures were performed through a single-trajectory approach. METHODS: A retrospective analysis of clinical notes, operation records, and pre- and postventriculostomy neuroimaging data was performed to determine the success or failure and complications of ETV and ETB in 42 patients presenting with tumor-induced obstructive hydrocephalus. Patient data were derived from an endoscopy database initiated in 1998. The study population included 21 female and 21 male patients (mean age 37 years, range 5-77 years). All 42 patients underwent an ETV; 33 of the 42 underwent an ETV and an ETB (single-trajectory). One patient was excluded from the follow-up analysis due to rapid deterioration of his condition from tumor progression. The duration of follow up ranged from 3 to 84 months (mean 32 months). At the last follow up, 11 patients with ETVs had undergone shunt placement and two patients had undergone repeated ETVs, giving a long-term success rate of 68% (28 of 41 cases) for single ETV as a treatment for hydrocephalus at presentation. Statistical analysis revealed no significant relationship (p > 0.92) between tumor location and ETV success or failure. The mean time to ETV failure was 32 weeks. Histological examination of biopsy specimens was non-diagnostic in eight (24%) of the 33 cases in which ETB was performed. Seven of these cases involved pineal region tumors and one involved a tectal plate tumor. There was no death or major morbidity associated with ETV and ETB in this series. CONCLUSIONS: Endoscopic third ventriculostomy is a safe and durable means of controlling hydrocephalus in tumor cases. Its success rate is high--comparable to that reported in aqueduct stenosis cases. Although ETB is probably not as accurate for diagnosis as biopsy with frame-based stereotactic guidance, it is associated with a lower mortality rate and, in the correct clinical setting, may be justifiably attempted as an initial biopsy procedure at the same time as ETV via a single-trajectory approach.

Adolescent↗
PubMed2001

Time-to-passage judgments on circular trajectories are based on relative optical acceleration.

Current theories of arrival time have difficulty explaining performance in the common but neglected case of nonlinear approach. Global tau, a variable supposed to guide time-to-passage (TTP) judgments of objects approaching on linear trajectories, does not apply to circular movement. However, TTP judgments are surprisingly accurate in such cases. We simulated movement through a three-dimensional cloud of point-lights on various circular trajectories. Arrival-time judgments were found to be above chance when observers had to determine which of two expansionless targets would pass them first. Similar to the inside bias observed in heading studies on circular trajectories, observers showed a strong bias to select the target on the inside of their own curved motion path as passing by first. Analysis of the projected target motion revealed that targets on the inside had lower optical velocities and relatively high optical acceleration rates. Empirical TTP judgments agreed best with a strategy based on relative optical velocity changes.

Adult↗
PubMed2004

Dynamical trajectories in category learning.

Category learning has traditionally been studied by examining how percentage correct changes with experience (i.e., in the form of learning curves). An alternative and more powerful approach is to examine dynamical learning trajectories--that is, to examine how the parameters that describe the current state of the model change with experience. We describe results from a new experimental paradigm in which empirical-learning trajectories are directly observable. In these experiments, participants learned two categories of spatial position, and they were constrained to identify and use a linear decision bound on every trial. The dependent variables of principal interest were the slope and the intercept of the bound used on each trial. Data from two experiments supported the following conclusions. (1) Gradient descent provided a poor description of the empirical trajectories. (2) The magnitude of changes in decision strategy decreased with experience at a rate that was faster than that predicted by gradient descent. (3) Learning curves suffered from substantial identifiability problems.

Cues↗