Biomedical subjects
Publications and source records attributed to S A Wallace.
Scrutiny of the family pedigrees of a population-based series of 176 children diagnosed with Wilms' tumor between 1954 and 1990, along with a review of the literature on the Li-Fraumeni cancer family syndrome, indicate that Wilms' tumor may be an uncommon component of the syndrome and that a small proportion of children with Wilms' tumor may be members of Li-Fraumeni syndrome (LFS) families.
Alcohol has become a major public health problem in the UK. In order to coordinate the work of both statutory and non-statutory agencies more efficiently and effectively, a government circular HN(89)4 has emphasized the need for development of local multi-agency alcohol misuse prevention strategies. Despite expressed enthusiasm for alcohol strategies, information about their development, effectiveness and overall national progress is scarce and needs to be improved. This national survey reports the most recent and accurate information about the development of district and regional alcohol strategies in England and Wales. Although only 51 (27%) districts stated they had a strategy, it was encouraging to find 90 (47%) other districts that were in the process of, or planning to develop such a document. Of the 51 districts with a strategy, the following key findings were noted: (1) Forty-three (84%) districts stated that they had started to implement their strategy, but none claimed to have fully implemented it. (2) Thirty-six (71%) districts stated that their strategy had an action plan. (3) Thirty-four (67%) districts stated that their strategy had been officially endorsed by the district health authority. (4) Thirty-eight (76%) districts stated that they had identified an individual or group to monitor the strategies' implementation. The results of the survey could be of interest to the Department of Health, the Faculty of Public Health Medicine, the Health Education Authority and the regional alcohol coordinators.(ABSTRACT TRUNCATED AT 250 WORDS)
Seven breast cancer families are examined for evidence of linkage to a site in the region of 17q12-q21, by using five markers. The families constitute a subset of a larger series of familial breast cancer; the seven families were selected because constitutional DNA was available on informative members, either from clinical samples or extracted from paraffin blocks. Two-point lod scores are reported. The maximum lod score, 0.8824, is obtained with marker NM23 at theta = 0. This is clearly not significant in itself; however, when taken in context with evidence from existing reports, it provides support for linkage to this region.
Subjects performed two patterns of coordination between the elbow and wrist joints of the right arm: 1) wrist flexion synchronized with elbow flexion and wrist extension with elbow extension (homologous muscle groups); and 2) wrist extension synchronized with elbow flexion and wrist flexion with elbow extension (nonhomologous muscle groups). As a parameter, cycling frequency, was increased, an abrupt switch in the phase relation between the elbow and wrist joints occurred. Similar effects were observed in underlying neuromuscular (EMG) timing patterns. Observed transitions depended on whether the forearm was prone or supine, not simply on the muscle pairing across the joints. With the forearm supine, transitions were from pattern (2) to pattern (1) above, and with the forearm prone the transitions were from pattern (1) to pattern (2). When subjects were initially prepared in pattern (1) with the forearm supine or in pattern (2) with the forearm prone, switching did not occur. En route to transitions, enhanced fluctuations in the phase relation occurred, indicating that loss of stability is at the origin of pattern change. Accompanying such changes in coordination were characteristic effects on end effector trajectories and velocity profiles. Possible neurophysiological mechanisms for context dependence in multijoint coordination are discussed.
The clinical syndrome of pure motor hemiparesis occurs with lacunar lesions in the internal capsule or in the basis pontis in hypertensive adults. It has been described in three patients with brain stem tumors of which two were children. A 3 1/2 years old boy with a brain stem tumor which presented as pure motor hemiparesis is described.
Three experiments were conducted to investigate the control of the manipulation (i.e., finger-thumb aperture) and transportation (i.e., wrist velocity) components in prehensile movement (Jeannerod, 1981, 1984). In all experiments, subjects were seated and instructed to grasp a dowel mounted on a joystick following a discrete movement over a set distance. Thus, the amount of dowel movement following the grasp could be determined. In Experiment 1, the tolerance (i.e., the amount of allowable dowel movement) was manipulated using a computer-generated boundary around the dowel. The results indicated that the transportation component changed dependent on the tolerance condition, and there were trends that maximum aperture was also affected. Experiment 2 manipulated both tolerance and dowel size (i.e., diameter) factorially in a within-subject design. Dowel size affected only the manipulation component, supporting Jeannerod's (1981) earlier work, but tolerance clearly influenced both components. Experiment 3 investigated Wing, Turton, and Fraser's (1986) proposition that speed of movement influences aperture size. Distance and movement time were combined factorially to produce conditions with different average velocities. Maximum aperture was dependent on the movement time rather than the speed of movement. The relation between the control of the components was examined by using a new method of calculating within-trial correlations between aperture size and wrist velocity in Experiments 2 and 3. The correlations were related to the temporal aspects of the movement with higher correlations in the rapid movement time conditions. Also, the temporal occurrence of maximum aperture remained invariant across the different movement conditions. In general, the results suggest a strong functional linkage between the two components, which may be dependent on the temporal characteristics of the movement.
Can one's limb be accurately positioned to a spatial location without a veridical estimate of the initial conditions of movement? The experiment reported here examined this question by distorting perception of a limb's starting position via muscle vibration. Subjects executed rapid flexion movements under no-vibration, contralateral arm vibration, and ipsilateral arm vibration conditions. Vibration was applied to the biceps for 10 sec prior to the start of a reproduction movement. The results showed that vibration on the ipsilateral arm caused a significant increase in reproduction error, relative to the no-vibration and contralateral-vibration conditions. This finding provides additional evidence that accurate knowledge about the initial conditions of movement is a necessary component in positioning a limb.
Explore the source record for details and available documents.
The experiment examined the effects of movement time (MT) and distance on the timing at electromyographic (EMG) activity from an agonist and antagonist muscle during rapid, discrete elbow movements in the horizontal plane. According to impulse-timing theory (Wallace, 1981) MT, not distance moved, should have a pronounced effect on the timing of EMG activity (duration of initial agonist and antagonist burst and time to onset of initial antagonist burst). The levels of MT were 100 and 160 msec and the levels of distance were 27 degrees and 45 degrees of elbow flexion. In general support of impulse-timing theory, the results of the three EMG timing measures showed that MT had a more pronounced effect on these measures than distance. In addition, the timing of EMG activity in relation to total MT remained fairly consistent across the four MT-distance conditions.
Much remains to be learned about how agonist and antagonist muscles are controlled during the production of rapid, voluntary movements. In an effort to summarize a wide body of existing knowledge and stimulate future research on this subject, an impulse-timing theory is presented which attempts to predict the activity of reciprocal muscles based on certain characteristics of a movement. The basic tenet of the theory is that variables of movement time, movement distance and inertial load have fairly predictable effects on the underlying muscular activity of the agonist and antagonist muscles during the production of rapid and discrete, voluntary movements. The theory is derived from the kinematic work of Schmidt, Zelaznik, Hawkins, Frank and Quinn (1979) and supporting evidence from studies which have used electromyographic (EMG) recordings of agonist and antagonist muscles during rapid movements. Issues related to synergistic muscle control, central and peripheral control of reciprocal muscle activity, muscle control, and neurological disorder and the relationship between impulse-timing and mass-spring control are discussed in the final section.
A basic tenet of both current closed-loop theories of motor learning (Adams, 1971; Schmidt, 1975) is that the generation of response specifications during learning is required for the development of recall memory. Two experiments were performed to test this tenet by attempting to demonstrate the development of recall memory in the absence of response specification production. The task in both experiments required blindfolded subjects to learn to produce a rapid, novel criterion movement on a linear positioning device. Control subjects in both experiments actively produced movements during learning with knowledge of results (KR) while experimental subjects in Experiment 1 experienced only the endpoint locations and in Experiment 2 were passively moved to the endpoint locations. Following initial KR trials, both experimental and control groups attempted to actively produce the criterion movement in the absence of KR. The results of both experiments support closed-loop theory that active practice is required to develop recall memory. There was some suggestion, however, that passive experience with sensory feedback may also aid recall memory development, contrary to the two closed-loop theories.
Explore the source record for details and available documents.
The decision time (reaction time [RT]) and movement time of retarded persons as a function of the amplitude and precision of a discrete movement in both simple and choice RT paradigms was examined. The results showed that RT for retarded persons was considerably longer and more variable than for nonretarded persons. Movement difficulty only elevated RT with both populations in the choice RT paradigm, and the RT regression coefficient for the retarded subjects was considerably greater than that for the the nonretarded group. Retarded subjects' movement time was significantly slower than that of the nonretarded subjects. Movement difficulty elevated movement time for both populations, as defined by Fitts's (1954) law. The slope of the movement-time regression coefficients was significantly higher for retarded persons and did not change across 5 days of practice. These findings suggest that information-processing differences in motor skills between populations can be attributed to response parameters.
Explore the source record for details and available documents.
Explore the source record for details and available documents.
Recent studies by Jones (1974) have posited that accurate movements in short-term motor memory (STMM) are mediated by the subject's ability to preset effector mechanisms and monitor their efferent output. Three experiments were conducted to examine this hypothesis. Experiment 1 involved comparisons between the reproduction of the end-location and the reproduction of the distance of a preselected movement. The results revealed that preselected location was superior to preselected distance, indicating that the efference attached to movement extent was not primary. Experiment 2 examined whether location cues were primarily encoded independent of the movement presentation mode. The subjects recalled target locations under preselected, constrained, and passive movement conditions. Recall in the preselected condition was superior to that in the constrained and passive conditions, which showed no difference, suggesting that afferent location information per se was not totally responsible for recall accuracy. Experiment 3 examined the processing requirements of preselected, constrained, and passive location information by filling the retention interval with interpolated processing activity. While preselected location was clearly superior, the three conditions were not differentially affected by processing activity. These overall findings were interpreted as contrary to Jones (1974) and pointed to the importance of preselection in short-term motor memory.
Explore the source record for details and available documents.
Explore the source record for details and available documents.