Estelle Palluel

The lasting effects of spike insoles on postural control in the elderly.

The purpose of the present study was to explore the lasting effects of a tactile sensitivity enhancement induced by spike insoles on the control of stance in the elderly. Healthy elderly subjects (n = 19, mean age = 68.8) and young adults (n = 17, mean age = 24.3) were instructed to stand or to walk for 5 minutes with sandals equipped with spike insoles. Postural control was evaluated four times during unperturbed stance: (1) before putting on the sandals equipped with spike insoles, (2) 5 minutes after standing or walking with them, (3) immediately after placing thin, smooth, and flexible insoles (no spike insoles) into the sandals to avoid the cutaneous contact with the spikes, and (4) after a sitting rest of 5 minutes with the no spike insoles. Sway parameters such as surface area, mean speed and root mean square were recorded. The present results suggest that (1) whatever the session (i.e. standing or walking) and the population, the artificial sensory message elicited by the spikes improved postural sway and, (2) the elderly were particularly perturbed when the tactile sensitivity enhancement device was removed. Whatever the age, the enriched sensory context provided by this tactile sensitivity enhancement device led to a better postural control; its suppression entailed a reweighting of the plantar cutaneous information. The difficulty that the elderly had to adjust the relative contribution of the different inputs probably reflected their poorer central integrative mechanisms for the reconfiguration of the postural set. A reduced peripheral sensitivity may also explain these postural deficits.

Leg muscle vibration modulates bodily self-consciousness: integration of proprioceptive, visual, and tactile signals

Behavioral studies have used visuo-tactile conflicts between a participants body and a visually presented fake or virtual body to investigate the importance of bodily perception for self-consciousness (bodily self-consciousness). Illusory self-identification with a fake body and changes in tactile processing--modulation of visuo-tactile cross-modal congruency effects (CCEs)--were reported in previous findings. Although proprioceptive signals are deemed important for bodily self-consciousness, their contribution to the representation of the full body has not been studied. Here we investigated whether and how self-identification and tactile processing (CCE magnitude) could be modified by altering proprioceptive signals with 80-Hz vibrations at the legs. Participants made elevation judgments of tactile cues (while ignoring nearby lights) during synchronous and asynchronous stroking of a seen fake body. We found that proprioceptive signals during vibrations altered the magnitude of self-identification and mislocalization of touch (CCE) in a synchrony-dependent fashion: we observed an increase of self-identification and CCE magnitude during asynchronous stroking. In a second control experiment we studied whether proprioceptive signals per se, or those from the lower limbs in particular, were essential for these changes. We applied vibrations at the upper limbs (which provide no information about the position of the participants body in space) and in this case observed no modulation of bodily self-consciousness or tactile perception. These data link proprioceptive signals from the legs that are conveyed through the dorsal column-medial lemniscal pathway to bodily self-consciousness. We discuss their integration with bodily signals from vision and touch for full-body representations.

Virtual reality improves embodiment and neuropathic pain caused by spinal cord injury

Objective: To investigate changes in body ownership and chronic neuropathic pain in patients with spinal cord injury (SCI) using multisensory own body illusions and virtual reality (VR). Methods: Twenty patients with SCI with paraplegia and 20 healthy control participants (HC) participated in 2 factorial, randomized, repeated-measures design studies. In the virtual leg illusion (VLI), we applied asynchronous or synchronous visuotactile stimulation to the participants back (either immediately above the lesion level or at the shoulder) and to the virtual legs as seen on a VR head-mounted display. We tested the effect of the VLI on the sense of leg ownership (questionnaires) and on perceived neuropathic pain (visual analogue scale pain ratings). We compared illusory leg ownership with illusory global body ownership (induced in the full body illusion [FBI]), by applying asynchronous or synchronous visuotactile stimulation to the participants back and the back of a virtual body as seen on a head-mounted display. Results: Our data show that patients with SCI are less sensitive to multisensory stimulations inducing illusory leg ownership (as compared to HC) and that leg ownership decreased with time since SCI. In contrast, we found no differences between groups in global body ownership as tested in the FBI. VLI and FBI were both associated with mild analgesia that was only during the VLI specific for synchronous visuotactile stimulation and the lower back position. Conclusions: The present findings show that VR exposure using multisensory stimulation differently affected leg vs body ownership, and is associated with mild analgesia with potential for SCI neurorehabilitation protocols.

Experimental changes in bodily self-consciousness are tuned to the frequency sensitivity of proprioceptive fibres

Several lines of evidence suggest an important implication of proprioceptive signals in bodily self-consciousness. By manipulating proprioceptive signals using muscle vibration, here, we investigated whether such effects depend on the vibration frequency by testing three different vibratory stimuli applied at the lower limbs (20, 40 and 80 Hz). We thus explored whether frequency-specific proprioceptive interference that has been reported in postural or motor tasks will also be found for measures of bodily self-consciousness. Self-identification (questionnaires) and visuotactile integration (asking participants to make tactile discriminations) were quantified during synchronous and asynchronous stroking conditions that are known to manipulate bodily self-consciousness. We found that even though muscle vibrations were applied at the same body location in all cases, 20 Hz vibrations did not alter the magnitude of self-identification and visuotactile integration, whereas 40 and 80 Hz vibrations did. These frequency-specific effects extend earlier vibration effects on motor and postural tasks to bodily self-consciousness. We suggest that the observed changes in bodily self-consciousness are due to altered proprioceptive signals from the lower limbs and that these changes depend on the tuning of Ia fibres to muscle vibration.

Evolución de las estrategias posturales desde la infancia a la adolescencia

El desarrollo de las estrategias de mantenimiento del equilibrio postural y locomotor durante la infancia y la adolescencia no es lineal. Dichas estrategias alcanzan su madurez en la edad adulta. En el transcurso de esta larga adquisicion se observan varios periodos de transicion. Numerosos factores contribuyen de manera determinante en la buena (normal) o mala (patologica) adquisicion de las estrategias posturales y locomotrices. Las caracteristicas filogeneticas y ontogeneticas, el aprovechamiento de las informaciones sensoriales, la estabilizacion cefalica y pelvica, ademas del gasto atencional, son factores que deben considerarse para comprender los patrones del desarrollo postural y locomotor en el ser humano. Suele suceder que algunas anomalias como la marcha digitigrada, la torsion del esqueleto, la enfermedad motriz cerebral o el autismo perturban el desarrollo postural, por lo que es fundamental profundizar en su conocimiento.