Effects of haptic supplementation on postural stability in unilateral vestibular loss patients

Light touch alters vestibular-evoked balance responses: insights into dynamics of sensorimotor reweighting

Integrated multisensory feedback plays a crucial role in balance control. Minimal fingertip contact with a surface (light touch), reduces the center of pressure (CoP) by adding sensory information about postural orientation and balance state. Electrical vestibular stimulation (EVS) can increase sway by adding erroneous vestibular cues. This juxtaposition of conflicting sensory cues can be exploited to explore the dynamics of sensorimotor adaptations. We used continuous stochastic EVS (0-25 Hz; ±4 mA; 200-300 s) to evoke balance responses in CoP (experiment 1, experiment 2). Systems analyses (coherence, gain) quantified coupling and size of balance responses to EVS. We had participants either touch (TOUCH; <2 N) or not touch (NO-TOUCH) a load cell during EVS (experiment 1, experiment 2), or we intermittently removed the touch surface (experiment 2) to measure the effects of light touch on vestibular-evoked balance responses. We hypothesized that coherence and gain between EVS and CoP would decrease, consistent with the central nervous system (CNS) down-weighting vestibular cues that conflict with light touch. Light touch reduced CoP displacement but increased variation in the CoP signal explained by EVS input. Significant coherence between EVS and CoP was observed up to ∼30 Hz in both conditions but was significantly greater in the TOUCH condition from 12 to 28.5 Hz. Conversely, EVS-CoP gain was 63% lower in TOUCH compared with NO-TOUCH. Our findings show that light touch can reduce the size of vestibular-evoked responses but also increase high-frequency vestibular contributions for sway. This suggests that the CNS can use discrete changes in sensory inputs to alter balance behavior but cannot fully suppress responses to a potent cue.NEW & NOTEWORTHY This study reveals that minimal fingertip contact (light touch) during balance tasks not only diminishes the impact of electrical vestibular stimulation (EVS) on sway but also exposes a high-frequency center of pressure element, correlated to vestibular inputs, not typically seen in free standing. Specifically, light touch decreases the magnitude of EVS-induced sway while increasing coherence with EVS at higher frequencies. This illustrates the central nervous system's capacity to adaptively reweight sensorimotor processes for balance control.

Changes of spatial and temporal characteristics of dynamic postural control in children with typical neurodevelopment with age: Results of a multicenter pediatric study

BACKGROUND

The aim of this multicenter study is to investigate the effect of chronological age and gender in postural control.

METHODS

To approach an ecological model, we used a multicenter posturography assessment. We analyzed postural control with surface, mean velocity of center of pressure [CoP] and temporal analysis, with Postural Instability Index [PII] being a more sensitive parameter in postural evaluation. A large sample of 156 age- and gender-matched healthy children recruited in several pediatrics hospitals, participated.

RESULTS

Our current results showed a significant decrease of all postural parameters (surface, mean velocity of CoP and PII) with age, and only on stable support condition. Our study additionally described a gender effect in conditions where all sensory inputs are most challenged with a mean velocity of CoP being significantly smaller in girls with respect to boys.

CONCLUSION

We concluded that postural control improves with age linked with maturation process. Moreover, this maturation process seems not yet achieved at 16.08 years and still ongoing beyond. Interestingly, our result reported specificities linked with gender effect. Indeed, girls and boys do not proceed in the same way to maintain their postural control. We could make hypothesis that more children maintain their postural control efficiently; with a low energy cost, the more they could allocate attention to learning during childhood.

Balance in Blind Subjects: Cane and Fingertip Touch Induce Similar Extent and Promptness of Stance Stabilization

Subjects with low vision often use a cane when standing and walking autonomously in everyday life. One aim of this study was to assess differences in the body stabilizing effect produced by the contact of the cane with the ground or by the fingertip touch of a firm surface. Another aim was to estimate the promptness of balance stabilization (or destabilization) on adding (or withdrawing) the haptic input from cane or fingertip. Twelve blind subjects and two subjects with severe visual impairment participated in two experimental protocols while maintaining the tandem Romberg posture on a force platform. In one protocol, subjects lowered the cane to a second platform on the ground and lifted it in sequence at their own pace. In the other protocol, they touched an instrumented pad with the index finger and withdrew the finger from the pad in sequence. In both protocols, subjects were asked to exert a force not granting mechanical stabilization. Under steady-state condition, the finger touch or the contact of the cane with the ground significantly reduced (to ∼78% and ∼86%, respectively) the amplitude of medio-lateral oscillation of the centre of foot pressure (CoP). Oscillation then increased when haptic information was removed. The delay to the change in body oscillation after the haptic shift was longer for addition than withdrawal of the haptic information (∼1.4 s and ∼0.7 s, respectively; p < 0.001), but was not different between the two haptic conditions (finger and cane). Similar stabilizing effects of input from cane on the ground and from fingertip touch, and similar latencies to integrate haptic cue from both sources, suggest that the process of integration of the input for balance control is initiated by the haptic stimulus at the interface cane-hand. Use of a tool is as helpful as the fingertip input, and does not produce different stabilization. Further, the latencies to haptic cue integration (from fingertip or cane) are similar to those previously found in a group of sighted subjects, suggesting that integration delays for automatic balance stabilization are not modified by visual impairment. Haptic input from a tool is easily exploited by the neural circuits subserving automatic balance stabilization in blind people, and its use should be enforced by sensory-enhancing devices and appropriate training.