Cortical facilitation of somatosensory inputs using gravity-related tactile information in humans with vestibular hypofunction

Abstract

A few years after their bilateral vestibular loss, patients usually show a motor repertoire that is almost back to normal. This recovery is thought to involve an up-regulation of the visual and proprioceptive information that compensates for the lack of vestibular information. Here, we investigated whether plantar tactile inputs, which provide body information relative to the ground and to the Earth-vertical, contribute to this compensation. More specifically, we tested the hypothesis that somatosensory cortex response to electric stimulation of the plantar sole in standing adults will be greater in humans (n = 10) with bilateral vestibular hypofunction (VH) than in an age-matched healthy group (n = 10). Showing significantly greater somatosensory evoked potentials (i.e., P1N1) in VH than in controls, the electroencephalographic recordings supported this hypothesis. Furthermore, we found evidence that increasing the differential pressure between both feet, by adding a 1 kg mass at each pendant wrist, enhanced the internal representation of body orientation and motion relative to a gravitational reference frame. The large decrease in alpha power in the right posterior parietal cortex (and not in the left) is in line with this assumption. Finally, behavioral analyses showed that trunk oscillations were smaller than head oscillations in VH and showed a reverse pattern for healthy participants. These findings are consistent with a tactile-based postural control strategy in the absence of vestibular input, and a vestibular-based control strategy in healthy participants where the head serves as a reference for balance control.

When mechanical engineering inspired from physiology improves postural-related somatosensory processes

“…Further evidence for the relevance of plantar sensory feedback comes from a study showing that blindfolded human participants are able to scale their postural adjustments according to near-threshold tactile stimulation evoked by small lateral acceleration (~ 0.2 m/s 2 ) of the supporting surface before mediation of vestibular or proprioceptive feedback 2 . Interestingly, Fabre and colleagues 8 recently reported in patients with bilateral vestibular loss that during quiet standing the response of the sensorimotor cortex to foot cutaneous stimulations (light electrical stimulation) was much greater than in age-matched healthy participants.…”

Seeing the piles of the velvet bending under our finger sliding over a tactile stimulator improves the perception of the fabric

“…Specifically, this procedure necessitated local pressure of the fingertip during the exploratory movement to provide more detailed properties (e.g., softness, thickness, relief) as Giboreau et al (2001). Our second approach is based on the current consensus that functional processing of sensory inputs is associated with the modulation of band-specific neural oscillation power (Fabre et al, 2023;Haegens et al, 2011;Pfurtscheller and Lopes da Silva, 1999). Notably, ongoing oscillations would shape our perception.…”

Investigating cortical activity during cybersickness by fNIRS

“…Motion sickness is a condition in which symptoms such as nausea, vomiting, and dizziness appear singly or in combination that occur in situations where acceleration and deceleration are repeated 1 , 2 . The human nervous system maintains balance and perceives body movements based on vestibular, visual, and somatosensory information 3 , 4 . For instance, if vision is fixed on one place when speed changes while moving in a boat or car, the brain receives conflicting vestibular and visual information, which can cause motion sickness 2 , 5 .…”