Biology subjects

Guehl, D.

Publications and source records attributed to Guehl, D..

4 recordsLinked to original sources

bioRxiv2026

Swung and spun in weightlessness : Evidence of immediate canalar underdetection of rotations in parabolic flight

Despite extensive research on vestibular function in microgravity, particularly during orbital and parabolic flight exposure, several gaps remain regarding the spontaneous behavior of vestibular organs under non-terrestrial gravitoinertial conditions. In particular, semicircular canal function, typically assessed through vestibulo-ocular reflex (VOR) recordings, has yielded inconsistent findings, with reports describing either no effect or reduced performance in microgravity. Moreover, many of these studies are limited by methodological constraints that reduce the interpretability of their conclusions. To clarify these discrepancies, we evaluated horizontal and vertical VOR responses during parabolic flights to assess semicircular canal function under transient weightlessness. Participants were passively rotated at a constant frequency and amplitude during normogravity and microgravity phases, centered along the heads vertical or inter-aural axis. Eye movements were recorded binocularly using infrared eye-tracking in darkness to eliminate visual influences, while participants were tightly restrained to minimize proprioceptive variability. Results show a reduction in VOR gain during microgravity in both axes, despite consistent rotational stimulation across gravity conditions. In addition, VOR gain remained reduced after parabolas in the horizontal plane, whereas vertical VOR performance was preserved. These are the first results to demonstrate an immediate alteration of semicircular canal function in weightlessness. Possible sources of the reduction in VOR performance in 0g are discussed. We also propose that the observed post-flight effects reflect a down-weighting of semicircular canal inputs during multisensory integration.

neuroscience↗

bioRxiv2026

Turning green in microgravity: facial color changes as best physiological indicator of space sickness

ABSTRACTMotion sickness (MS) is commonly hypothesized to arise from sensory conflicts between incongruent sources of sensory information. Different types of sensory conflicts can induce MS, yet it remains unclear whether distinct contexts produce different physiological responses. Moreover, there is a lack of reliable objective predictors of MS, particularly for space motion sickness (SMS), which appears unrelated to motion sickness susceptibility on Earth. This study examined multiple physiological measures as potential objective markers of MS, including heart rate, blood pressure, salivary cortisol, skin conductance, skin surface temperature, and facial skin colorimetry. Subjective motion sickness severity and symptomatology were assessed using standardized questionnaires (SSQ, MSAQ, MSSQ). All measures were collected before and immediately after exposure to two sensory conflict paradigms: virtual reality (visuo-vestibular conflict) and parabolic flight (otolitho-canal conflict). Post-exposure, both paradigms were associated with increased cortisol, skin conductance, and skin greeness. Notably, increased skin greenness was associated with greater MS severity in parabolic flight and strongly correlated with subjective nausea ratings in both paradigms. Skin temperature and systolic blood were affected differently by VR and parabolic flight. No robust new physiological predictors of MS were identified. Overall, our findings suggest that facial skin color -particularly skin greenness- may serve as a simple, non-invasive, and reliable objective indicator of MS severity.

neuroscience↗

bioRxiv2025

Visual and vestibular reweighting after cyber- and space-sickness

Sensory conflicts are widely recognized as the primary drivers of motion sickness (MS), though the underlying integrative processes remain poorly understood. This study investigated sensory reweighting that follows exposure to different sensory conflict paradigms. First, visual and vestibular reflexes were assessed before and after a visuo-vestibular conflict induced by purely visual stimulation in virtual reality. Second, visual and vestibular integration were evaluated before and after an otolith-canal conflict induced by gravitational changes in parabolic flight. Semi-circular canal integration was measured via the vestibuloocular reflex (VOR) suppression task, while visual weighting was assessed through optokinetic nystagmus (OKN). Our findings revealed that different sensory conflict paradigms elicit distinct sensory reweighting processes. Visuo-vestibular conflict resulted in a decreased VOR response, whereas vestibulo-vestibular conflict mainly led to a reduction in OKN following parabolic flight. Sensory down-weighting occured in the modality that did not detected displacement, likely perceived as the less reliable input, regardless of its accuracy. Additionally, visual sensitivity emerged as a potential predictor of cybersickness, while vestibular sensitivity seemed to influence MS severity in parabolic flight. Our data suggest that the sensitivity of the most stimulated sensory modality during a given conflict may determine an individuals susceptibility to MS. KEY POINTSO_LISensory reweighting occur through brief and specific exposure to motion sickness. C_LIO_LIAdaptive reweighting is modulated by the nature of the motion sickness exposure, with distinct effects observed between space-sickness and Earth-like motion sickness cues. C_LIO_LIMotionless cues are consistently downweighted, regardless of their accuracy. C_LIO_LIMotion sickness intensity depends on individuals sensitivity to the stimulated sensory sources, which varies across provocative sensory environments. C_LI

neuroscience↗

bioRxiv2019

Ancestral persistence of vestibulo-spinal reflexes in axial muscles in humans

Accurate control of the trunk is essential for maintaining balance in an upright subject. Most studies addressing vestibulo-spinal reflexes have investigated the role of the lower limbs, while limited attention has been paid to the back muscles. To address this issue, we challenged the persistence of vestibular evoked myogenic potentials (VEMPs) in back muscles in situations in which the leg muscle responses were modulated. Nineteen subjects were submitted to galvanic vestibular stimulations (GVS). Body sway and VEMPs were recorded in the paraspinal and limb muscles. During treadmill locomotion, the VEMPS in the lower limbs were observed only during the stance phase, whereas the axial VEMPs were observed during all phases. In upright standing subjects, slight head contact was sufficient to abolish the VEMPs in the lower limbs, while the VEMPs remained present in the paraspinal muscles. Similarly, during parabolic flight-induced microgravity, the VEMPs in the lower limb muscles were suppressed, while those in the axial muscles persisted despite the absence of gravitational information from the otolithic system. Our results depict a differentiated control mechanism of axial and appendicular muscles when a perturbation is detected by vestibular inputs. The persistent feature of axial myogenic adjustments suggests that a hard-wired reflex is functionally efficient to maintain posture. By contrast, the ankle responses to perturbations occur only when the accompanying sensory feedback is congruent, challenging the balance task and gravity. Overall, this study using GVS in microgravity is the first to present an approach delineating feed-forward vestibular control in the absence of all feedback.

neuroscience↗