Vestibular signal processing in a subject with somatosensory deafferentation: The case of sitting posture

<p>Abstract</p> <p>Background</p> <p>The vestibular system of the inner ear provides information about head translation/rotation in space and about the orientation of the head with respect to the gravitoinertial vector. It also largely contributes to the control of posture through vestibulospinal pathways. Testing an individual severely deprived of somatosensory information below the nose, we investigated if equilibrium can be maintained while seated on the sole basis of this information.</p> <p>Results</p> <p>Although she was unstable, the deafferented subject (DS) was able to remain seated with the eyes closed in the absence of feet, arm and back supports. However, with the head unconsciously rotated towards the left or right shoulder, the DS's instability markedly increased. Small electrical stimulations of the vestibular apparatus produced large body tilts in the DS contrary to control subjects who did not show clear postural responses to the stimulations.</p> <p>Conclusion</p> <p>The results of the present experiment show that in the lack of vision and somatosensory information, vestibular signal processing allows the maintenance of an active sitting posture (i.e. without back or side rests). When head orientation changes with respect to the trunk, in the absence of vision, the lack of cervical information prevents the transformation of the head-centered vestibular information into a trunk-centered frame of reference of body motion. For the normal subjects, this latter frame of reference enables proper postural adjustments through vestibular signal processing, irrespectively of the orientation of the head with respect to the trunk.</p

Obesity Impact on the Attentional Cost for Controlling Posture

International audienceBACKGROUND: This study investigated the effects of obesity on attentional resources allocated to postural control in seating and unipedal standing. METHODS: Ten 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. INTERPRETATION: Obese 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

Pointing to a target from an upright position in human: tuning of postural responses when there is target uncertainty

International audienceHuman subjects performed, from a standing position, rapid hand pointings to visual targets located within or beyond the prehension space. To examine the interaction between posture and the goal-directed movement we introduced a visual double-step perturbation requiring a reprogramming of the hand movement. Trials directed towards the same spatial goal but differentiated only by the likeliness of a visual double-step were compared. The hand kinematics was not affected by the uncertainty of the visual perturbation; an increased trunk bending, however, was observed. This suggests that uncertainty constraints are integrated in a predictive manner for the optimal coordination of the hand and postural control systems. (C) 2000 Elsevier Science Ireland Ltd. All rights reserved

Aging and postural control: postural perturbations caused by changing the visual anchor.

OBJECTIVE: To determine the effect of modifying the stable visual anchor on the postural stability of older individuals. The visual anchor was changed by opening doors similar to those found in an elevator cage. Lighting intensities inside and outside the cage were varied to create increasing or decreasing luminosity conditions. The effect of adding a cognitive load (counting backwards) was also tested. DESIGN: A controlled laboratory study. SETTING: Tests performed in a balance laboratory. MEASUREMENTS: Sensory and clinical measurements to insure the integrity of the central and peripheral nervous system. Measures of balance were derived from the recordings of the center of foot pressure. These measures included range and speed of the center of foot pressure. PARTICIPANTS: Eight older, community-dwelling subjects and nine young subjects participated. A sensorimotor evaluation was used to insure that all older individuals were free from any pathologies affecting postural stability. All participants had a low score (indicating high balance confidence) on the Falls Efficacy Scale and no history of falls. RESULTS: Older individuals were affected by modification of the stable visual anchor induced by the opening of doors similar to that of an elevator cage. They showed greater ranges of the center of foot pressure (COP) and speed of the COP after than before the opening of the doors. Furthermore, the increased ranges and speed were two to three times greater than that observed for the young subjects. A lighting intensity considered as comfortable for reading inside the elevator affected the overall postural stability of the older participants negatively. Counting backwards also decreased their overall stability. CONCLUSION: Changing the stable visual anchor, as when exiting an elevator cage, could be a significant risk factor for older persons. Moreover, when combined with a cognitive load or lower lighting intensity inside the elevator cage, the negative effects on the postural stability of older persons are exacerbated

Postural imbalance in non-treated adolescent idiopathic scoliosis at different periods of progression

The aim of this study was to test the hypothesis that imbalance in patients with a severe deformity of the spine is associated with an increase in the sensory integration disorder. This paper is a case comparison study. Patients were divided into three groups: able-bodied (n = 53), observation (n = 23), and pre-brace (n = 26) groups. Time domain parameters (sway area, position and displacement) and structural posturographic parameters [mean distance (MD) and mean peak (MP)] were calculated from the COP excursion using a force platform. A sensory integration disorder could be an important factor in the progression of the scoliotic curve. Significant differences were found in time domain between observation, pre-brace and able-bodied groups. The results for the structural posturographic parameters showed significant differences between the pre-brace and the able-bodied groups (P = 0.018 MD and P = 0.02 MP) demonstrating a perturbation in sensory integration system by an increase of imbalance. The absence of statistical difference between the observation and the pre-brace groups for the structural posturographic parameters indicates a perturbation of sensory integration system associated with curve progression. Our study has demonstrated that the pre-brace group is less stable than the able-bodied group. The severity of scoliosis in pre-brace scoliotic girls could be related to an increase in the sensory integration disorder