Luc Maynard

Hemispheric specificity for proprioception: Postural control of standing following right or left hemisphere damage during ankle tendon vibration.

Right brain damage (RBD) following stroke often causes significant postural instability. In standing (without vision), patients with RBD are more unstable than those with left brain damage (LBD). We hypothesised that this postural instability would relate to the cortical integration of proprioceptive afferents. The aim of this study was to use tendon vibration to investigate whether these changes were specific to the paretic or non-paretic limbs. 14 LBD, 12 RBD patients and 20 healthy subjects were included. Displacement of the Centre of Pressure (CoP) was recorded during quiet standing, then during 3 vibration conditions (80 Hz - 20s): paretic limb, non-paretic limb (left and right limbs for control subjects) and bilateral. Vibration was applied separately to the peroneal and Achilles tendons. Mean antero-posterior position of the CoP, variability and velocity were calculated before (4s), during and after (24s) vibration. For all parameters, the strongest perturbation was during Achilles vibrations. The Achilles non-paretic condition induced a larger backward displacement than the Achilles paretic condition. This condition caused specific behaviour on the velocity: the LBD group was perturbed at the onset of the vibrations, but gradually recovered their stability; the RBD group was significantly perturbed thereafter. After bilateral Achilles vibration, RBD patients required the most time to restore initial posture. The reduction in use of information from the paretic limb may be a central strategy to deal with risk-of-fall situations such as during Achilles vibration. The postural behaviour is profoundly altered by lesions of the right hemisphere when proprioception is perturbed.

Neglect following stroke: The role of sensory sensitivity in visuo-spatial performance

Both proprioceptive and visual manipulations have led to some improvement of the spatial neglect syndrome. Until now, their effects on visuo-spatial behaviour have never been compared simultaneously. The objective of this study was to determine their influence, as a function of the presence of neglect and the side of the brain damage. 19 stroke patients with right and 14 with left brain damage, without or with neglect; realized the Bells test in 5 conditions: a reference condition and 4 sensory conditions, defined according to the side of application (contralesional vs ipsilesional) and the type of perturbation (visual vs proprioceptive). The visuo-spatial behaviour was analyzed for global and spatial aspects and for individual extreme performances. For the neglect group, the restriction of the visual field to the ipsilesional hemi-field significantly diverted the centre of exploration towards the ipsilesional side compared to all other conditions. The weighting of visual cues from the ipsilesional hemi-field seems to be increased in sensory-motor integration processes in neglect patients. In all the groups, although some improvements in performance did occur with sensory manipulation, they were dependent on the individual, particularly for neglect patients. A same performance can be achieved through the use of different sensory-motor strategies, which are individual-related. It is thus important to consider the sensory sensitivity and the responsiveness of each patient before beginning any sensory therapies.

Effects of aging in postural strategies during a seated auto-stabilization task

Impaired sensory, motor and central processing systems combining with biomechanical changes are risk of fall factors in the elderly population. The aim of this study was to assess the auto-adaptation and the regulation of the dynamic control of equilibrium in age-related adaptive strategies, by using a seated position on a seesaw. 15 young adults and 12 healthy middle-aged adults were asked to actively maintain a sitting posture as stable as possible during 12.8s, on a 1-degree of freedom seesaw (auto-stabilization paradigm), with and without vision. The seesaw was placed in order to allow roll or pitch oscillations. We determine length and surfaces CoP shifts, mean positions and variability, a Postural Performance Index (PI) and a Strategy Organization Ratio (SOR). Our results shows that adopted strategies are plane-dependant during auto-stabilization (parallel and perpendicular axes control is impacted) and age-dependant. PIx during roll seated auto-stabilization tasks appears as the most relevant parameter of aged-related instability. The visual effect, during pitch auto-stabilization, characterizes the postural sensory-motor human behavior. The quantitative and qualitative postural assessment, thanks to seated auto-stabilization task, need to be promoted for long-term health care and probably for the rehabilitation of various disorders.