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  • 1
    ISSN: 1432-1106
    Keywords: EMG patterns ; Motor programming ; Ballistic movements
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary EMG patterns associated with voluntary wrist flexion movements were studied in normal human subjects. Initially, subjects were trained to produce movements within five specified velocity ranges while the amplitude of the movement and the opposing load remained constant. In a second set of experiments, subjects were required to produce movements at four different amplitudes, moving as rapidly as possible against a constant load. Finally, with movement velocity and amplitude kept constant, the external load was varied so that different forces were required to generate the movements. The slowest movements were associated with a prolonged burst of EMG activity from the agonist muscle with little or no antagonist activity. With increasing movement velocity, there was a gradual evolution to the characteristic “triphasic” pattern associated with rapid voluntary movements. As velocity of movement increased further, the amplitude and area of the EMG bursts increased while burst duration and interburst intervals decreased. Increases in movement amplitude were accomplished mainly by changing the timing of the EMG bursts; with larger amplitude movements the antagonist burst occurred later. With movements against larger loads there was an increase in the size of the agonist burst and a decrease in the antagonist burst, but no change in the relative timing of the EMG bursts. These systematic changes in EMG patterns associated with different types of movement provide an indirect method of obtaining information concerning the motor programs which generate the movements.
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  • 2
    ISSN: 1432-1106
    Keywords: Limb movements ; Visually guided reaching ; Visual motion processing ; Latency ; Human
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary We have evaluated the use of visual information about the movement of a target in two tasks tracking and interceptions — involving multi-joint reaching movements with the arm. Target velocity was either varied in a pseudorandom order (random condition) or was kept constant (predictable condition) across trials. Response latency decreased as target velocity increased in each condition. A simple model that assumes that latency is the sum of two components — the time taken for target motion to be detected, and a fixed processing time — provides a good fit to the data. Results from a step-ramp experiment, in which the target stepped a small distance immediately preceding the onset of the ramp motion, were consistent with this model. The characteristics of the first 100 ms of the response depended on the amount of information about target motion available to the subject. In the tracking task with randomly varied target velocities, the initial changes in hand velocity were largely independent of target velocity. In contrast, when the velocity was predictable the initial hand velocity depended on target velocity. Analogously, the initial changes in the direction of hand motion in the interception task were independent of target velocity in the random condition, but depended on target velocity in the predictable condition. The time course for development of response dependence was estimated by controlling the amount of visual information about target velocity available to the subject before the onset of limb movement. The results suggest that when target velocity was random, hand movement started before visual motion processing was complete. The response was subsequently adjusted after target velocity was computed. Subjects displayed idiosyncratic strategies during the catch-up phase in the tracking task. The peak hand velocity depended on target velocity and was similar for all subjects. The time at which the peak occurred, in contrast, varied substantially among subjects. In the interception task the hand paths were straighter in the predictable than in the random condition. This appeared to be the result of making adjustments in movement direction in the former condition to correct for initially inappropriate responses.
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  • 3
    ISSN: 1432-1106
    Keywords: Long latency reflexes ; Electromyographic activity ; Wrist muscles ; Humans
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary Reflex EMG responses to angular displacements of the wrist joint were recorded from 12 normal human volunteers. A mechanical stop was used to suddenly arrest displacements at varying times following the onset of the stimulus. With unrestricted movement of the handle, the EMG response consisted of an early component (M1) with a latency of 30–35 ms and a long-latency component (M2–3) beginning 55–65 ms after the onset of the displacement. When the displacements were arrested prior to a critical time occurring between 40 and 50 ms after the onset (mean of 44 ms), the M2–3 component of the response was not present. Increasing the duration of the displacement beyond this time resulted in a rapid increase in the size of M2–3. Facilitation provided by volitional intent to oppose the perturbation was not sufficient to generate an M2–3 response to either a brief, low velocity displacement produced by the torque motor or to a phasic, high velocity stretch produced by a tendon tap. The timing relationships between the onset latency of M2 and the minimum duration of displacement required to generate an M2–3 response are not easily reconciled with the notion that the segmentation of the EMG responses into components is mediated by repeated activation of the same central reflex pathway by phasic afferent bursts. Two mechanisms that could account for these results are either inhibition in response to the sudden stop of phasically-active “linking” interneurons which are part of the long latency pathway, or the loss of an essential convergent facilitatory input which serves to monitor the continuation of the movement.
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  • 4
    ISSN: 1432-1106
    Keywords: Key words Cerebellar patients ; Double-step paradigm ; Pointing movement ; Kinematic analysis ; Human
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract  Three patients with cerebellar limb ataxia and three age-matched controls performed arm-pointing movements towards a visual stimulus during an experimental procedure using a double-step paradigm in a three-dimensional space. Four types of trajectories were defined: P1, single-step pointing movement towards the visual stimulus in the initial position S1; P2, double-step pointing movement towards S1; P3, double-step straight pointing movement towards the second position S2; and P4, double-step pointing movement towards S2 with an initial direction towards S1. We found that the cerebellar patients, as well as the controls, were able to modify their motor programs, but with impaired timing, severe anomalies in the direction and amplitude of the changed movement trajectories and alteration of the precision of the pointing movements.
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  • 5
    ISSN: 1432-1106
    Keywords: Limb movements ; Visually guided reaching ; Retinal Extraretinal ; Human
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract We have assessed the contribution made by retinal and extraretinal signals when subjects used their hand to track targets moving at constant velocities. Comparisons were made between responses produced under the following conditions: (1) with full vision of the hand and unrestricted movement of the eyes, (2) without vision of the hand or (3) while visually fixating a stationary LED. Target velocity was varied in a pseudo-random order across trials. In each condition response latency decreased as target velocity was increased. There was a ∼24 ms increase in latency when vision of the hand was removed or eye movements were restricted. Under normal conditions, subjects were able to accurately catch up to and match target velocity with their hand. When vision of the hand was removed, subjects lagged behind the target but were able to match target velocity. This deficit was eliminated when vision of the hand was made available for the beginning of the response. When subjects were required to visually fixate they could catch up to the target with their hand, but subsequently produced a steady state hand velocity that was greater than target velocity. When the LED was positioned such that the target started in the peripheral visual field, the overestimation of target velocity was evident from the beginning of the response: subjects produced initial accelerations with their hand that were significantly greater than in normal conditions. Finally, normal responses were produced when subjects were required to visually pursue a second target that moved at the same speed and in the same direction as the main target. When the velocities of these two targets differed, subjects produced hand movements that were initially more appropriate for the target being visually pursued. Together these results suggest that vision of the hand and how it is initially positioned relative to the target is necessary to catch up to the target; whereas the extraretinal signal concerned with eye velocity is required to produce an accurate steady state hand velocity.
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  • 6
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    Clinical rheumatology 4 (1985), S. 212-217 
    ISSN: 1434-9949
    Keywords: Amyloidosis ; Amyloid Arthropathy ; Multiple Myeloma ; Erosive Arthropathy
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary Amyloid arthropathy is said to be distinguished roentgenographically from rheumatoid arthritis by the absence of joint space narrowing and the absence of articular erosions. We present a patient with multiple myeloma with swelling, stiffness and firm synovial thickening of the wrists, metacarpophalangeal joints and proximal interphalangeal joints whose hand radiographs showed articular erosions of the carpal joints and ulnar styloid and joint space narrowing of the proximal interphalangeal joints and metacarpophalangeal joints. Synovial biopsy of the left wrist showed amyloid deposits with no inflammation. Previous reports of X-ray changes in amyloid arthropathy note preservation of joint spaces or widening. Erosions when noted are of non-articular bone rather than of the articular surface. This is the first case report of erosive articular disease in amyloid arthropathy.
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  • 7
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
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  • 8
    ISSN: 1432-1939
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary The numbers, dispersal behavior, aging and residence, and Wrightian neighborhood configurations of three species of Colias butterflies have been studied in central Colorado, using mark-release-recapture techniques as major tools. All populations studied have nonoverlapping generations and mature one brood each year. A brief general review of these species' autecology is given. A system for measuring degree of physical damage to the adults is introduced. This “wear rating” varies with temporal position of any given sample in the course of a brood's flight season, the insects becoming progressively more damaged with time. The sex ratio also changes with brood aging: males eclose before females, and are in the majority early in the flight season, while females may predominate at the end of flight. Local population numbers for the montane grassland species C. alexandra may reach peak levels of 700–900 insects in favorable years, but be much lower in other years as a result of, e.g., drought. Peak densities are no more than 2/ha. The montane bog species, C. scudderi, maintains comparable low density but has much smaller local populations. The subalpine/alpine grassland species C. meadii displays peak local numbers as high as 3000, with peak density as high as 120/hectare. Dispersal varies both among and within species. Those C. alexandra who disperse show an average dispersal radius of about 1.3 km, with a radius for the whole population of about 0.6 km; maximum distance moved was 8 km. Dispersal proportions among recaptures are sharply curtailed by adverse weather, but the dispersal radius of those moving is unaffected by weather. C. scudderi's dispersal is strongly influenced by the geometry of its bog and streamside habitats. Some C. meadii populations approach isolated “island” status, but others show much dispersal. Dispersal radius of those dispersing ranges from 0.3 to 0.7 km in different populations, but the proportion of dispersals varies greatly. The longest observed movement by this species is 1.3 km, although up to 2.6 km could have been detected. Colias normally display constant loss (death plus emigration) rates with average residence expectations of 4–6 days; few insects reach their maximum physiological lifespan of approximately 1 month. Bad weather can increase the loss rate drastically. Females show shorter residence than males, appearently as a result of greater mortality. Total-numbers-per-brood estimates are given for our better studied populations. The reproductive strategy of Colias is such that Wright's models for neighborhood size apply. Neighborhood size for C. alexandra varied sixfold in numbers, and from 3 to 1.3 km in physical extent, between a favorable year and a drought year. One localized C. scudderi habitat is only 200 m in diameter, but a streamside population has a neighborhood length of 4.8 km. In C. meadii, one population of 2000–2500 insects is an 8-ha “island”, while another of similar numbers extends a single neighborhood across 1.9 km distance, 450 m altitude, and a major ecological boundary (timberline). Factors such as weather, individuals' visual cueing, and thermoregulatory behavior can influence population structure. For some Colias populations, selection may be very uniform within neighborhoods, while for others, single neighborhoods cross sharp discontinuities in selective forces. These patterns may differ for different selective forces, and may also vary with stages of the insects' life cycle. these populations will now prove a valuable resource for studying evolutionary population genetics.
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  • 9
    ISSN: 1573-4927
    Keywords: homologous linkage groups ; hemoglobin ; Peromyscus ; Mus ; Rattus ; glucosephosphate isomerase
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Abstract In Mus musculus, family Muridae, the glucosephosphate isomerase (Gpi-1), pink-eyed dilution (p), albinism (c), and β-type globin (Hbb) loci are known to be linked in the order Gpi-1-p-c-Hbb. In Rattus norvegicus, another murid rodent, the p, c, and Hbb loci are known to be linked in the same order and with similar recombination frequencies. In Peromyscus maniculatus, family Cricetidae, it was previously known that p and c are linked and by analogy to Mus musculus that linkage group should be bounded by Gpi-1 near p and by a β-globin locus near c. Linkage has now been established between Gpi-1 and the Hbe globin locus in Peromyscus. However, the observed recombination frequency in Peromyscus (16.3%) is significantly lower than in Mus, suggesting that perhaps a chromosomal inversion has occurred during the evolutionary divergence of the two rodent families. Linkage relationships were also tested between the Hbc 1, Hbd 1, and Hbe 1 globin variants. Hbc 1 (presumably an α-type globin) segregated independently from Hbd 1 and Hbe 1 (presumably β-type globins). No recombination was observed between Hbd 1 and Hbe 1. Those two globin genes may be alleles at a single locus, although circumstantial evidence suggests that they represent tightly linked duplicate loci.
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  • 10
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The electronic structure of the low-temperature phosphorescencent probe 6-thioguanine was investigated. Structural transitions in some alcohols (ethanol, glycerol, propanediol) were obtained using this probe in the range 4.2-273 K. Aqueous solutions of native and denatured DNA and those of native DNA with propanediol and DMSO added were studied in the range of 4.2-273 K. The analysis of the luminescence spectra of DNA solutions permits the assumption of the energy transfer to the probe on UV radiation of DNA. © 1994 John Wiley & Sons, Inc.
    Additional Material: 5 Ill.
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