Strength of the perception action coupling in human body discrimination tasks.

Perceiving and extracting information from others rely on functional Perception Action Coupling. Because motor experiences influence the strength of the perception action coupling, we explored the duality between vision and proprioceptive information about the self and others in body perception using a sequential same-different visual task from 6 to 7 years old to adults. Using a same-different matching task combined with congruent or incongruent action execution, this study explored in 30 children (M ± SD: 9.2 ± 1.5; 16♀), 33 adolescents (M ± SD: 14.7 ± 1.5; 16♀) and 28 adults (M ± SD: 29.5 ± 6.5; 12♀) how the congruence of the perception action coupling could influence the body representation building in memorizing and discriminating other's postures. The first result revealed better performances to perceive other's body postural changes compared to objects' shapes modifications as early as 6-7 years old. Nevertheless, this ability needs a long time to mature as reflected by the lower performances in children compared to older groups, i.e. adolescents and young adults. In addition, executing a congruent action during the encoding phase increased the RT, reflecting involvement of additional cognitive processes of self-other correspondence, without improving the performance accuracy, due to a slow maturation of multimodal body representations. On the other hand, executing an incongruent action during the encoding phase revealed an interference effect to perceive others' posture, demonstrated by the decrease of performance accuracy. As we initially hypothesized, the strength of perception action coupling appears to be modulated by age. Indeed, the interference effect had a greater impact in adolescents involved in a different judgment of two body postures. Therefore, the assessment of the perception action coupling may predict the body representation maturity in typical development or internal body representation dysfunction in neurodevelopmental disorders.

Subthalamic Deep Brain Stimulation Modulates Proprioceptive Integration in Parkinson's Disease During a Postural Task.

Defective proprioceptive integration may play a role in the pathophysiology of motor symptoms in Parkinson's disease (PD). Dysfunction related to proprioceptively-evoked postural reactions in PD patients is still a controversial issue, with only a limited number of studies to date and mostly discordant results. The aims of the present study were (1) to determine whether or not the proprioceptive defect in PD underlies postural impairment and (2) whether or not deep brain stimulation of the subthalamic nucleus (STN-DBS) affects proprioceptive integration. We examined proprioceptive integration during a postural task in 13 PD patients and 12 age-matched control subjects, using a muscle-tendon vibration paradigm. Analysis of the center of pressure displacement and kinematic data indicates a greater degree of postural destabilization and a reduced ability to maintain a vertical orientation in PD. We found a significant positive effect of STN-DBS on these postural features. Our findings indicate that Parkinson patients, even in the absence of any clinical evidence of instability, falls, or freezing, use proprioceptive information for postural control less efficiently than healthy subjects. Furthermore, STN-DBS was found to improve proprioceptive integration, with positive impacts on postural orientation and balance.

Body schema building during childhood and adolescence: a neurosensory approach.

In order to perceive and act in its environment, the individual's body and its interactions with the sensory and social environment are represented in the brain. This internal representation of the moving body segments is labeled the body schema. Throughout life, body schema develops based on the sensory information used by the moving body and by its interactions with the environment including other people. Internal representations including body schema and representations of the outside world develop with learning and actions throughout ontogenesis and are constantly updated based on different sensory inputs. The aim of this review is to present some concepts and experimental data about body schema, internal representations and updating process during childhood and adolescence, as obtained using a neurosensory approach. From our developmental studies, it was possible to explore the slow maturation of the sensorimotor representations by examining the anticipatory control. By manipulating proprioceptive and visual information, which are at the heart of the construction of body schema, we wished to highlight notable differences between adolescents and young adults on both a postural and perceptual level, which confirms the late maturation of multisensory integration for central motor control.

Updating process of internal models of action as assessed from motor and postural strategies in children.

The objective of this study was to investigate the updating process of internal models of action in children and young adults, through the postural and motor strategies adopted in simple tasks, namely sit-to-stand (STS) and back-to-sit (BTS). To this end, 11 healthy children from 7 to 10years (latest stage of childhood) and 12 healthy adults participated in the experiment. The STS and BTS tasks were performed with horizontal support surface and support surface tilted 10° to the right or forward in order to investigate the immediate adaptation of the internal representations of the movement. Movement variables that included the durations of STS and BTS and the amplitudes of the trunk movement were computed. Postural characteristics were also considered during the transition from STS to BTS, including the trunk orientation and the head stabilization strategies. Despite certain similarities with adults, especially in terms of the asymmetry of the performance times for the two tasks (STS vs. BTS) and the partial movement adaptations, the children were less able than adults to adapt both postural and movement controls to the new support conditions. Thus, it appears that the updating of internal models of action is a process that matures slowly throughout ontogenesis.

A limit-cycle model of leg movements in cross-country skiing and its adjustments with fatigue.

Using dynamical modeling tools, the aim of the study was to establish a minimal model reproducing leg movements in cross-country skiing, and to evaluate the eventual adjustments of this model with fatigue. The participants (N=8) skied on a treadmill at 90% of their maximal oxygen consumption, up to exhaustion, using the diagonal stride technique. Qualitative analysis of leg kinematics portrayed in phase planes, Hooke planes, and velocity profiles suggested the inclusion in the model of a linear stiffness and an asymmetric van der Pol-type nonlinear damping. Quantitative analysis revealed that this model reproduced the observed kinematics patterns of the leg with adequacy, accounting for 87% of the variance. A rising influence of the stiffness term and a dropping influence of the damping terms were also evidenced with fatigue. The meaning of these changes was discussed in the framework of motor control.

Effects of fatigue on inter-cycle variability in cross-country skiing.

The aim of the study was to examine the inter-cycle variability in cross-country skiing gait and its evolution with fatigue. Both issues were investigated to understand the flexibility capabilities of the neuromuscular system. Four women and four men skied on a treadmill, up to exhaustion. The angular displacements of the arms and legs movements were obtained for 40s period at the beginning and end of the skiing test. Mean inter-cycle standard deviation (SD(c)), largest Lyapunov exponent (lambda(1)) and correlation dimension (D(c)) were computed for each time series and surrogate counterpart to evaluate the magnitude and nature of the variability. For any experimental time series, lambda(1) was positive, D(c) greater than 1 and both were found to be different from their surrogate counterparts, confirming that the temporal variations of the data had a deterministic origin. More, larger SD(c), D(c) and lambda(1) values were observed at the end of the test, indicating more variability, noise and local dynamic instability in the data with fatigue. Hence, the fluctuations of limb angular displacements displayed a chaotic behavior, which reflected flexibility of the neuromuscular system to adapt to possible perturbations during skiing. However, such chaotic behavior degraded with fatigue, making the neuromuscular system less adaptable and more unstable.

Dynamics of coordination in cross-country skiing.

The aim of the present study was to identify modes of coordination in cross-country skiing from a dynamical systems perspective. Participants (N=8) skied on a treadmill using classical techniques with varying steepness (i.e., 0 degrees-7 degrees). Coordination was evaluated in terms of the relative frequency and relative phase between upper arms and thighs. Results revealed that the limb movements were systematically attracted towards low integer frequency ratios (i.e., 1:1 and 2:1) and in-phase (phi approximately 0 degrees ) and anti-phase relationships (phi approximately 180 degrees). The increase in steepness produced shifts between the attractive modes of limb movements and a loss of stability was observed during transitions. These results suggest that principles of coordination between limbs in cross-country skiing are akin to those of non-linear coupled oscillators, as documented for a broad range of motor activities. Yet, differences with such classical findings are discussed reflecting the specific biomechanical constraints of cross-country skiing.

Sjögren's syndrome in progressive systemic sclerosis.

Thirty-five consecutive patients with progressive systemic sclerosis were prospectively evaluated for evidence of Sjögren's syndrome. Six of the 35 (17%) were judged to have the disorder. This is a higher prevalence than in most reports, but much lower than that recently reportedly by Alarcón-Segovia and associates (7). An additional 17 of the 35 patients (48%) had significant fibrosis in the absence of sufficient mononuclear cell infiltrates to confirm the diagnosis of Sjögren's syndrome. This group had particularly aggressive scleroderma with serious visceral features, and five died after a short duration of illness. No significant abnormalities were found in biopsies from six patients with the mixed connective tissue disease syndrome, five with Raynaud's phenomenon alone, or in 29 autopsy control subjects who had no evidence of connective tissue disease. Fibrosis in the absence of mononuclear infiltration in minor salivary glands of patients with progressive systemic sclerosis indicates a poor prognosis.

Corneal perforation in Wegener's granulomatosis treated with corneal transplantation: case report.

A 46-year-old man with Wegener's granulomatosis developed corneal ulceration and descemetocele. He was treated with a penetrating keratoplasty which has remained clear for 22 months. With the increased life expectancy of this disease corneal rehabilitation is increasingly important and possible.

Penetrating keratoplasty in herpes simplex keratitis. Recurrence in grafts.

A review of 231 penetrating keratoplasties performed for corneal disease due to herpes simplex keratitis shows that clear grafts may be obtained in 75% and satisfactory visual results in about 70% during a long-term follow-up. Over a three-year follow-up period, recurrence of the herpetic disease in the graft was observed in 12%. Over a longer period of follow-up, up to 15 years, the rate of recurrence increased to 47%. About half of the corneas with recurrence achieved clear grafts with treatment. Recurrence did not appear to be less frequent in those cases which circumscribed scars as compared with those in which there was diffuse scarring. The state of activity of the disease preoperatively could not be demonstrated to influence greatly the results of the keratoplasty.