Giulia Zanelli

Vestibular and proprioceptive estimation of imposed rotation and spatial updating in standing subjects

The aim of the study was to evaluate in standing subjects their perception of whole-body rotation and spatial updating, and to determine whether the brain uses mainly angular velocity or rotational duration to re-orient the body. Ten healthy blindfolded adults stood barefoot on a horizontal rotating platform. Participants had to maintain their balance while being passively rotated by a platform through 45°, 90°, 135°, 180° and 360°, clockwise (CW) and counter-clockwise (CCW). At the end of platform rotation, participants had to give their estimation of the angle. They then had to actively reproduce it in the opposite direction. Three different conditions were applied: one which involved different peak cosinusoidal angular velocity profiles (18°/s, 35°/s, 53°/s, 71°/s and 141°/s) at constant duration of stimulus (4 s); one which involved different stimulus durations (1.25 s, 2.5 s, 3.75 s, 5 s and 10 s) at constant peak velocity (57°/s); and one where subjects had to reproduce a specific angle without prior stimulus imposed by the platform. In the reproduction phase, results show overestimation of stimulus from -180° to 180° in all three conditions; however, ±360° rotations were underestimated only in the first two conditions. Comparing stimulus perception and reproduction, the perceived angle corresponded to that reproduced in the range from -180° to 180°; however, ±360° angles were correctly perceived but inaccurately reproduced. Thus, the interconnection between movement and information via the vestibular/proprioceptive systems is essential to evaluate the body position in space; however, the spatial errors show the key importance of sight in correcting the errors caused by the cue integration.

Reach-to-grasp interjoint coordination for moving objects in children with hemiplegia

OBJECTIVE To evaluate interjoint coordination in children with hemiplegia as they reach to grasp objects, in both static and dynamic conditions. An ad hoc robotic device was used to study the dynamic condition. DESIGN Observational study. PATIENTS Six children with hemiplegia and 6 young adults. METHODS Kinematics of the trunk and arm were studied using an optoelectronic system. In the dynamic condition the target object, a cup, was moved by the robotic device along clockwise and counterclockwise circular trajectories. RESULTS Two main strategies were used to study the onset and offset of shoulder and elbow movements and their maximum velocities. The hand velocity profile was bell-shaped in the static condition and compatible with ramp movements for the more affected side in the dynamic condition. The time to object contact was higher for the more affected side in the dynamic condition. The temporal coordination index illustrated an immature and less flexible behaviour in childrens reaching in all the examined conditions. CONCLUSION Study of the hand velocity profiles, the time to object contact and the temporal coordination index highlighted, first, the dependence of upper limb interjoint coordination on task, context, residual resources and individual solution, and secondly, the sensory-motor deficit characteristics of the childrens more affected side during dynamic reaching, raising the prospect of a promising training context in children with hemiplegia.

Reorientation ability of adults and healthy children submitted to whole body horizontal rotations.

Many studies analysed the ability of blindfolded adults to perceive passive rotation and to orient themselves using the vestibular system. Ivanenko et al. (1997) imposed to sitting blindfolded subjects CCW rotations (45 , 90 , 135 , and 180 ) using a motorised chair (Robuter). They had to reproduce angles and the results showed angle overestimation, even if the same authors recognised a possible bias that could affect the results, caused by the imposing rotation always in the same direction. Siegler et al. (2000) used the same device to impose CW and CCW rotations to healthy blindfolded subjects; they compared the rotation directions and obtained no significant differences. Marlinsky (1999) rotated healthy blindfolded subjects by means of a manual turnable chair, at constant angular velocity and amplitude from 30 to 360 , both CW and CCW directions. The subjects still overestimated the passive turns; in reproduction, they overestimated small angles and underestimated the higher ones. Thus, a heterometric space was drawn, depending on the turn magnitude and direction. However, no statistically significant differences were determined between rotation directions both in perception and reproduction. Also in the paper by Okada et al. (1999), sitting subjects were rotated CW and CCW and the results were normalised for direction, because no asymmetries were observed. In other researches, a motorised turnable platform was used to impose CW and CCW rotations to blindfolded standing subjects (Jürgens et al. 1999; Becker et al. 2000); no significant difference between directions was noted. Finally, Metcalfe and Gresty (1992) compared perception of CW/CCW passive rotations, imposed by the Barany chair, in normal and vestibular subjects. Comparing directions, it was found that healthy subjects had the same ability in both hemispaces, while vestibular patients showed more difficulties towards the affected side. On the basis of the previously indicated findings we designed a horizontal rotating platform totally controlled via software, described in a previous paper (Cappa et al. 2008), to analyse, for the first time, orientation ability in standing subjects. The aim of our study was the evaluation of horizontal rotation by multisensory integration of vestibular plus proprioceptive information, in healthy children during perception and reproduction tasks. This method provides an interesting paradigm for testing both postural behaviour and memory of self-rotation.

Spatial rotational orientation ability in standing children with cerebral palsy

This study quantified perception and reorientation ability after passive horizontal rotations in thirteen children with cerebral palsy (CP). They stood barefoot on a platform in front of a fixed reference point (static posture task, SPT) and were then blindfolded and passively rotated with six velocity profiles (maximum angular velocity: 57°/s; rotation amplitudes: ±90°, ±180° and ±360°). After the perturbation, the blindfolded children were asked to point to the fixed reference point with their preferred hand (pointing task, PT) and to step back to the initial position on the stationary platform (reorientation task, RT). In order to gain further insight into rotational attitude, the results were comparatively examined with body segment rotations determined using standardized gait analysis (gait task, GT). The kinematic evaluations were conducted using an optoelectronic system: for SPT, PT and RT we confined the analysis, in the horizontal plane, to the head and upper pointing arm of the subject and to the platform; for GT a full body analysis was performed. When CP children were passively rotated towards their more affected side, they overestimated the imposed angle in PT but under-reproduced it in RT. A higher variability emerged in left-hemiplegic children, confirming that the spatial disorganization is predominantly related to right brain lesion. Patients tended to rotate in GT towards the more affected side while in RT they showed an opposite trend.