BackgroundThis study investigated the effects of obesity on attentional resources allocated to postural control in seating and unipedal standing.MethodsTen non obese adults (BMI = 22.4±1.3, age = 42.4±15.1) and 10 obese adult patients (BMI = 35.2±2.8, age = 46.2±19.6) maintained postural stability on a force platform in two postural tasks (seated and unipedal). The two postural tasks were performed (1) alone and (2) in a dual-task paradigm in combination with an auditory reaction time task (RT). Performing the RT task together with the postural one was supposed to require some attentional resources that allowed estimating the attentional cost of postural control. 4 trials were performed in each condition for a total of 16 trials.Findings(1) Whereas seated non obese and obese patients exhibited similar centre of foot pressure oscillations (CoP), in the unipedal stance only obese patients strongly increased their CoP sway in comparison to controls. (2) Whatever the postural task, the additional RT task did not affect postural stability. (3) Seated, RT did not differ between the two groups. (4) RT strongly increased between the two postural conditions in the obese patients only, suggesting that body schema and the use of internal models was altered with obesity.InterpretationObese patients needed more attentional resources to control postural stability during unipedal stance than non obese participants. This was not the case in a more simple posture such as seating. To reduce the risk of fall as indicated by the critical values of CoP displacement, obese patients must dedicate a strong large part of their attentional resources to postural control, to the detriment of non-postural events. Obese patients were not able to easily perform multitasking as healthy adults do, reflecting weakened psycho-motor abilities.

The brain deformation that occurs during neurosurgery is a serious issue impacting the patient "safety" as well as the invasiveness of the brain surgery. Model-driven compensation is a realistic and efficient solution to solve this problem. However, a vital issue is the lack of reliable and easily obtainable patient-specific mechanical characteristics of the brain which, according to clinicians' experience, can vary considerably. We designed an aspiration device that is able to meet the very rigorous sterilization and handling process imposed during surgery, and especially neurosurgery. The device, which has no electronic component, is simple, light and can be considered as an ancillary instrument. The deformation of the aspirated tissue is imaged via a mirror using an external camera. This paper describes the experimental setup as well as its use during a specific neurosurgery. The experimental data was used to calibrate a continuous model. We show that we were able to extract an in vivo constitutive law of the brain elasticity: thus for the first time, measurements are carried out per-operatively on the patient, just before the resection of the brain parenchyma. This paper discloses the results of a difficult experiment and provide for the first time in vivo data on human brain elasticity. The results point out the softness as well as the highly non-linear behavior of the brain tissue.

Obese people suffer from postural deficits and are more subject to falls than their lean counterpart. To improve prevention and post-fall rehabilitation programs, it seems important to better understand the posturo-kinetic disorders in daily life situations by determining the contribution of some key factors, mainly morphological characteristics and physical activity level, in the apparition of these disorders.Twelve severe android obese and eight healthy non obese adults performed a reaching task mobilizing the whole body. To further determine the origin of the postural and motor behavior differences, non obese individuals also performed an experimental session with additional constraints which simulated some of the obese morphological characteristics. Impact of the sedentary lifestyle was also studied by dissociation of the obese in two subgroups: physically « active » and physically « inactive ». Movement kinetics and kinematics were characterized with an optoelectronic system synchronized to a force platform. The mechanical equilibrium pattern was evaluated through the displacements of the Centre of Mass (CoM) and the centre of foot pressure within the Base of Support (BoS).Results showed that obesity decreased movement speed (≈−23%, p<0.01), strongly increased CoM displacement (≈+30%, p<0.05) and induced an important spatio-temporal desynchronization (≈+40%, p<0.05) of the focal and postural components of the movement during the transition between the descending and ascending movements.The role of some morphological characteristics and of physical activity on obese patients' postural control disorder is discussed and set back in the more general context of overall factors contributing to postural deficits with obesity.