Telomere length is a crucial factor for both normal chromosomal function and senescence. Mean telomere length in humans shows considerable interindividual variation and strong genetic determination. To see if a locus (or loci) affecting telomere length in humans could be mapped, we performed a quantitative-trait linkage analysis of mean leukocyte telomere-restriction-fragment (TRF) lengths, measured by Southern blotting, in 383 adult subjects comprising 258 sib pairs. Heritability of mean (+/-SE) TRF was 81.9%+/-11.8%. There was significant linkage (LOD score 3.20) of mean TRF length to a locus on chromosome 12, which explained 49% of the overall variability in mean TRF length. We present preliminary analysis of a strong candidate gene in the region, the DNA helicase DDX11. In conclusion, we report mapping of the first locus that determines mean telomere length in humans. Identification of the gene involved and elucidation of its mechanism of action could have important implications for our understanding of chromosomal assembly, telomere biology, and susceptibility to age-related diseases.

The goal of the present study was to investigate how grip forces are applied when transferring stable control of an object from one person to another. We asked how grip forces would be modified by the passer to (1) control for inertial forces as the object was transported toward the receiver and (2) control for the impending perturbation when the receiver made contact with the object. Twelve volunteers worked in pairs during this experiment. One partner, playing the role of passer, transported an object with embedded load cells forward or held the object at an interception location. The second partner, playing the role of receiver, waited at an interception location or reached toward the passed object. Kinematic results indicated that while passers performed a stereotypical movement, receivers were sensitive to the motion of the object as they reached to make contact. Grip force results indicated that passers' grip forces and grip/load force ratios were variable on a trial-to-trial basis, suggesting that a refined internal model of the passing task was not achieved within the timeframe of the experiment. Furthermore, a decoupling of the temporal and magnitude characteristics of the grip and inertial forces was noted in conditions where passers transported the object toward the receiver. During object transfer, it was noted that passers used visual feedback-based anticipatory control to precisely time initial grip force release, while somatosensory control was used by both the passer and receiver to precisely coordinate transfer rate.

Four experiments examined the sensitivity of visual shor t-ter m memory to visual patter n similarity. Experiment 1 showed that immediate serial memory for novel visual patter ns was sensitive to similarity. U sing an item reocgnition task, Experiment 2 showed that subjects lear ned the descriptions of sets of similar and dissimilar patter ns at the same rate. But repeated presentations of patter ns in a serial m emor y task again showed a marked and per sistent similarity effect (Experiment 3). T he ® nal experiment showed the visual similarity effect in serial m emory for patter ns that had been previously lear ned. T he results show that (a) serial m em ory for patter ns is sensitive to visual sim ilarity, (b) the visual similar ity effect is not due to perceptual confusions but originates in memory, (c) there is a clear dissociation between item and order er rors, and (d) the visual similarity effect survives articulatory suppression. Visual serial order memory and verbal serial recall appear to share several of these properties, suggesting that the same constr aints gover n serial memory in each modality. Implications for the understanding of shor t-ter m memory are discussed. Recent work in this laboratory has drawn attention to the fact that studies of shor t-ter m memor y (ST M) for verbal materials, such as letters and words, com mon ly u se method s requiring explicit kn owledge of serial order, wh ereas stu dies of shor t-ter m visual memor y have usually tested m em ory for the con® gu ration of novel item s (Avons, 1998). O ne implication is that the marked ly d ifferent serial position curves, previously claim ed to be characteristic of different m od alities, may be the prod uct of a confound between materials and m eth od s. Phillips and his colleagues (Avons & Phillips, 1987; Ph illips, 1983; Phillips & Christie, 1977a, 1977b) stud ied serial position curves using random ly generated novel visual patter ns. T heir results showed no primacy and a labile recen cy effect that was con® ned to the last item p resented and ap peared on ly if this was also the ® rst item tested. In these stu dies, m emor y was tested by a series of recognition tests in wh ich subjects discriminated

This is the first study to identify a significant relationship between vitamin D levels and severity of head injury. Clinicians should actively screen for and treat VDD in head injured patients to reduce the risk of further morbidity such as osteomalacia and cardiovascular disease. Future research should establish the natural history of vitamin D levels following TBI to identify at which stage VDD develops and whether vitamin D replacement could have a beneficial effect on recovery and quality of life.

The present study examined the effects of a visual-based biofeedback training on improving balance challenges in autism spectrum disorder (ASD). Twenty-nine youth with ASD (7-17 years) completed an intensive 6-week biofeedback-based videogame balance training. Participants exhibited training-related balance improvements that significantly accounted for postural-sway improvements outside of training. Participants perceived the training as beneficial and enjoyable. Significant moderators of training included milder stereotyped and ritualistic behaviors and better starting balance. Neither IQ nor BMI moderated training. These results suggest that biofeedback-based balance training is associated with balance improvements in youth with ASD, most robustly in those with less severe repetitive behaviors and better starting balance. The training was perceived as motivating, further suggesting its efficacy and likelihood of use.

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Background The study aim was to evaluate validity evidence using idle time as a performance measure in open surgical skills assessment. Methods This pilot study tested psychomotor planning skills of surgical attendings (N=6), residents (N=4) and medical students (N=5) during suturing tasks of varying difficulty. Performance data were collected with a motion tracking system. Participants’ hand movements were analyzed for idle time, total operative time and path length. We hypothesized that there will be shorter idle times for more experienced individuals and on the easier tasks. Results A total of 365 idle periods were identified across all participants. Attendings had fewer idle periods during three specific procedure steps (p < .001). All participants had longer idle time on friable tissue (p < .005). Conclusion Using an experimental model, idle time was found to correlate with experience and motor planning when operating on increasingly difficult tissue types. Further work exploring idle time as a valid psychomotor measure is warranted.

The goal of the present study was to understand which characteristics (movement time or velocity) of target motion are important in the control and coordination of the transport and grasp-preshape components of prehensile movements during an interception task. Subjects were required to reach toward, grasp and lift an object as it entered a target area. Targets approached along a track at four velocities (500, 750, 1000 and 1250 mm/s) which were presented in two conditions. In the distance-controlled condition, targets moving at all velocities traveled the same distance. In the viewing-time-controlled condition, combinations of velocity and starting distances were performed such that the moving target was visible for 1000 ms for all trials. Analyses of kinematic data revealed that when, target distance was controlled, velocity affected all transport-dependent measures; however, when viewing time was controlled, these dependent measures were no longer affected by target velocity. Thus, the use of velocity information was limited in the viewing-time-controlled condition, and subjects used other information, such as target movement time, when generating the transport component of the prehensile movement. For the grasp-preshape component, both peak aperture and peak-aperture velocity increased as target velocity increased, regardless of condition, indicating that target velocity was used to control the spatial aspects of aperture formation. However, the timing of peak aperture was affected by target velocity in the distance-controlled condition, but not in the viewing-time-controlled condition. These results provide evidence for the autonomous generation of the spatial and temporal aspects of grasp preshape. Thus, an independence between the transport and grasp-preshape phases was found, whereby the use of target velocity as a source of information for generating the transport component was limited; however, target velocity was an important source of information in the grasp-preshape phase.