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    We now compare these limitations in younger and older adults during active or passive limb movements. Participants put their dominant hand on a robot arm and performed movements actively or the relaxed limb was moved passively. Either a distorted visual feedback or no visual feedback at all was provided during the movement. Perception of limb movements was attenuated through visual feedback. This effect was more pronounced in older adults. However, no difference between active and passive movements was found. The results provide evidence for the limited awareness of body effects, even in the absence of voluntary actions. Introduction Intentional actions commonly generate bimodal sensory effects: on the one hand the proximal, body-related action effects like the proprioceptive sensation from the required joints, and on the other hand the distal action effects, for example, the displacement of the cursor on the monitor. These sensory inputs must be monitored and integrated for online action control and error-based learning, especially in case of tool use, as demonstrated in a dual-feedback model Figure 1. The execution of motor commands produces spatial displacements of the body effector e. Sensory feedbacks of proximal and distal movement effects will be used to update the actual spatial configuration of the body effector and the tool. Based on these updates, new motor commands will be generated to continue the action in a modified way.

    In addition, the proprioceptive sensation per se may be not as precise as the visual perception. In the experiment of Van Beers et al. The precision of the visual localization was between 0. Taken together, the proprioceptive sensation of limb movements seems to be highly susceptible and less reliable than the visual sensation.

    Professor Steven Kelly

    Empirical evidence shows that humans are able to integrate multisensory signals in an optimized fashion to maximize the reliability of the perception Ernst and Banks, ; Drewing and Ernst, Considering a motor action as an object of perception, integration of sensory feedback from visual and proprioceptive senses should follow the same principle.

    Therefore, in connection with the aforementioned lack of reliability of proprioception, it makes perfect sense that vision dominates action control, since the variance of the visual estimation is lower than that of the proprioceptive estimation. The major question addressed in the current study is if there are any factors that moderate the bimodal integration, and consequently, affect the predominance of the visual feedback.

    We focused on two potential factors. A process-related factor could be the presence of motor commands.

    These can be understood as neural signals generated as exclusive sources of voluntary actions. Since motor commands build a link between distal and proximal action effects the movement mode should play an important role in information processing. The study by Zwickel et al. Judgments were significantly biased in the direction of the produced movement when movements were performed actively, whereas no such effect was observed for passive movements.

    Professor Steven Kelly

    Accordingly, we assume that the motor commands could enhance sensory integration and consequently strengthen the impact of distal feedback on proximal movement perception.

    A subject-related factor could be age.

    Mounting evidence suggests that declines in proprioceptive function represent a fundamental aspect of the aging process Adamo et al. A variety of age-related neurophysiological changes may account for the declines in proprioception. Changes in the peripheral nervous system as potential cause are for example decreased spindle diameter, decreased sensitivity of muscle spindles, decreased number of intrafusal fibers, and a decline in the number of joint mechanoreceptors for a comprehensive review see Goble et al.

    Declines in proprioceptive functions are also thought to be a result of changes in the central nervous systems, since increased proprioceptive processing demands were found to significantly impact the assessment of proprioceptive acuity in the elderly Stelmach et al. Based on these findings, we assume that the elderly would be more dependent on the visual feedback, which would then unfold its dominance more intensively. Finally, the following hypotheses were proposed: a Distorted visual feedback makes movement perception more difficult.

    To examine these hypotheses, the current study compared the performance in limb movement perception of older and younger adults in various feedback distorted visual feedback vs.

    Materials and Methods Participants In total eight younger participants five male , aged between 22 and 29 years mean: 25 years; SD: 2. All of them were right-handed and had normal or corrected-to-normal vision. Participants were all neurologically intact and had no known history of neuromotor disorders. Prior to the experiments, participants signed an informed consent statement.

    The robot presents redundant kinematics with seven degrees of freedom, allowing more complexity in the execution of the movements. Sensors evaluating the torque in each joint in real-time provide several useful features, for instance the compensation of the gravity and accelerated reaction when the robot is submitted to external forces.

    All triangles were isosceles with a constant horizontal base of 26 cm. The six standardized movement trajectories of the hand solid lines. For visual feedback an equal-sided right-angled triangle with dashed lines was constantly displayed. The participants sat on a chair in front of the robot arm Figure 3. The chair and the robot arm stood immovable through the experiment.

    The right shoulder of the participant and the resting robot arm on its start location were on the same sagittal plane. The distance between the shoulder of the participant and the robot arm was approximately 70 cm. Participants put their dominant hand on the robot arm and either performed the movement actively or the relaxed limb was moved passively. Every movement was constrained within one of the six pre-defined trajectories.

    Short audio signals pure tone with Hz for ms were provided to mark the beginning and the end of each movement.

    The audio signals were clearly audible to the participants, despite the ear protection they were wearing throughout the experiment. The distorted visual feedback consisted of a cursor a blue dot with a diameter of 3 mm moving along the sides of a static equilateral right-angled triangle with a base of 26 cm Figure 2 , dashed lines , which was presented centrally on the display.

    Schematic view of the set-up. With help of the robot, limb movements could be carried out passively or actively. A distorted visual feedback about the limb movement could be presented on a LCD monitor, left alongside the robot in front of the participant. Communication between the robot arm and the feedback monitor was facilitated by a MatLab Ra program on a Windows computer.

    The movement of the robot arm was proportionally transferred into cursor movement, depending on the ratio between the total length of the actual limb trajectory and the feedback triangle, so that the cursor appeared to be completely synchronized with the robot arm. The passive movements have pre-defined acceleration profiles and a constant duration of approximately 6 s.

    In catch trials the blue cursor indicating the movement brightened shortly yellow , which should be detected and reported by the participants as a secondary task. The experimenter registered the responses manually. Procedure The experiment was carried out in two consecutive sessions.

    In Session I, a trial started with an audio signal, after which the robot arm began to move. Starting from the vertex down left, the robot led the relaxed right hand of the participant to complete one of the six standardized trajectories. After another audio signal indicated the end of the movement, participants instantaneously estimated the shape of their unseen hand trajectory. Session I contained two blocks differing in feedback conditions: one block contained only trials with distorted visual feedback, while the other block contained only trials without visual feedback.

    The sequence of the blocks was counterbalanced across all participants. Every pre-defined trajectory was presented 15 times resulting in 90 trials per block.

    Prior to experimental trials 15 practice trials were provided to familiarize the participants with the task and its requirements. The whole session took about 60—70 min. At the end of the session participants were given a short questionnaire, in which they were asked about the strategy for making their estimations.

    Arthritis Rheum. Epub Oct Intercellular adhesion molecule-1 mediates the inhibitory effects of hyaluronan on interleukin-1beta-induced matrix metalloproteinase production in rheumatoid synovial fibroblasts via down-regulation of NF-kappaB and p Rheumatology Oxford.

    Epub Jan Expression of cannabinoid receptor 2 and its inhibitory effects on synovial fibroblasts in rheumatoid arthritis. Expression, regulation, and signaling of the pattern-recognition receptor nucleotide-binding oligomerization domain 2 in rheumatoid arthritis synovial fibroblasts. The effects of 1 alpha,dihydroxyvitamin D 3 on matrix metalloproteinase and prostaglandin E 2 production by cells of the rheumatoid lesion. Arthritis Res. Int J Mol Med. Epub Aug 9. CTGF promotes articular damage by increased proliferation of fibroblast-like synoviocytes in rheumatoid arthritis.

    Epub Mar Mol Med Rep. Epub Jun Early and stable upregulation of collagen type II, collagen type I and YKL40 expression levels in cartilage during early experimental osteoarthritis occurs independent of joint location and histological grading.

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    Arthritis Res Ther. Epub Dec 7. Apoptotic cell death is not a widespread phenomenon in normal aging and osteoarthritis human articular knee cartilage: a study of proliferation, programmed cell death apoptosis , and viability of chondrocytes in normal and osteoarthritic human knee cartilage. Arthritis Rheum. Correlation between interleukin-6 expression in articular cartilage bone and osteoarthritis. Genet Mol Res. Cartilage collagen damage in hip osteoarthritis similar to that seen in knee osteoarthritis; a case-control study of relationship between collagen, glycosaminoglycan and cartilage swelling.

    BMC Musculoskelet Disord. Epub Apr 6. Subchondral cyst development and MMP-1 expression during progression of osteoarthritis: an immunohistochemical study. Orthop Traumatol Surg Res.

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