Cortical facilitation of somatosensory inputs using gravity-related tactile information in patients with bilateral vestibular loss

Abstract

A few years after their bilateral vestibular loss, individuals 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 patients (n = 10) with bilateral vestibular loss than in an aged-matched healthy group (n = 10). Showing significant greater somatosensory evoked potentials (i.e., P1N1) in patients 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 pending wrist, enhanced the internal representation of body orientation and motion relative to a gravitational reference frame. The large decreased in alpha/beta power in the right posterior parietal cortex (and not in the left) is in line with this assumption. Finally, our behavioral analyses showed smaller body sway oscillations for patients, likely originated from a tactile-based control strategy. Conversely, healthy subjects showed smaller head oscillations suggesting a vestibular-based control strategy, the head serving as a reference for balance control.HighlightsSomatosensory cortex excitability is greater in patients with bilateral vestibular loss than in aged-matched healthy individualsTo control balance, healthy individuals “locked” the head while vestibular patients “locked” their pelvisFor vestibular patients, increasing loading/unloading mechanism enhances the internal representation of body state in the posterior parietal cortex

Guided by touch: Tactile Cues in Hand Movement Control

“…Indeed, the remarkable flexibility of the brain, its ability to dynamically control the transmission of afferent signals [18][19][20] , and the reliability of visual cues in controlling movements 21 converge to suggest that tactile involvement in motion control might be limited solely to contexts where hand vision is precluded, as was the case in Moscatelli et al 16 and Bettelani et al 17 . The increased responsiveness of the somatosensory cortex to foot tactile stimulation observed in individuals with impaired vestibular systems 22 supports the hypothesis of an upregulation of relevant tactile inputs in sensory impoverished contexts.…”

“…Importantly, the blindfolded approach used in their study may have altered the sensory weighting process of visuo-somatosensory signals, potentially attributing greater relative weight to the sense of touch compared to conditions where visual feedback is available. This possibility is supported by studies showing that sensory deprivation can potentiate spared sensory inputs, a phenomenon known as sensory substitution 22,[40][41][42][43] .…”

Prenatal origins of antigravity homeostasis in humans

“…Whilst the 'uprightness' approach can accommodate this finding post-hoc (by postulating that uprightness-based antigravity control is gain-controlled by load sensors [110,111]), it does not imply it. Indeed when humans lose their vestibular sense, they can adapt to manage balancing by load feedback [112]. Wider bodily antigravity mechano-homeostasis also scales with buoyant support over longer timescales; extended buoyant suspension induces losses in musculoskeletal condition similar to extended orbital microgravity [92].…”

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.…”