Changes in gain of horizontal vestibulo-ocular reflex during spaceflight

Effects of spaceflight on the brain

The number of long duration human spaceflights has increased substantially over the past 15 years, leading to the discovery of numerous effects on the CNS. Microgravity results in headward fluid shifts, ventricular expansion, an upward shift of the brain within the skull, and remodelling of grey and white matter. The fluid changes are correlated with changes to perivascular space and spaceflight associated neuro-ocular syndrome. Microgravity alters the vestibular processing of head tilt and results in reduced tactile and proprioceptive inputs during spaceflight. Sensory adaptation is reflected in postflight effects, evident as transient sensorimotor impairment. Another major concern is that galactic cosmic radiation, which spacefarers will be exposed to when going beyond the magnetosphere around Earth, might have a negative effect on CNS function. Research with rodents points to the potential disruptive effects of space radiation on blood-brain barrier integrity and brain structures. More work is needed to understand and mitigate these effects on the CNS before humans travel to Mars, as the flight durations will be longer than anyone has previously experienced.

Diagnostic Value of the Vestibular Autorotation Test in Menière's Disease, Vestibular Migraine and Menière's Disease with Migraine

(1) Background: Vestibular migraine (VM) and Menière's disease (MD) share multiple features in terms of clinical presentations and auditory-vestibular functions, and, therefore, more accurate diagnostic tools to distinguish between the two disorders are needed. (2) Methods: The study was of retrospective design and examined the data of 69 MD patients, 79 VM patients and 72 MD with migraine patients. Five vestibular autorotation test (VAT) parameters, i.e., horizontal gain/phase, vertical gain/phase and asymmetry were subjected to logistic regression. The receiver operating characteristic (ROC) curves were generated to determine the accuracy of the different parameters in the differential diagnosis of MD and VM. (3) Results: Our results showed that the horizontal gain of VAT significantly outperformed other parameters in distinguishing MD and VM. In addition, the sensitivity, specificity and accuracy of the horizontal gain were 95.7%, 50.6% and 71.6%, respectively, for the differentiation between VM and MD. In most MD patients, the horizontal gain decreased in the range of 3-4 Hz, while in most VM patients, horizontal gain increased in the range between 2-3 Hz. More MD with migraine patients had an increased horizontal gain when the frequency was less than 5.0 Hz and had a decreased horizontal gain when the frequency was greater than 5.0 Hz. (4) Conclusion: Our study suggested the VAT, especially the horizontal gain, as an indicator, may serve as a sensitive and objective indicator that helps distinguish between MD and VM. Moreover, VAT, due to its non-invasive and all-frequency nature, might be an important part of a test battery.

Neuro-consequences of the spaceflight environment

As human space exploration advances to establish a permanent presence beyond the Low Earth Orbit (LEO) with NASA's Artemis mission, researchers are striving to understand and address the health challenges of living and working in the spaceflight environment. Exposure to ionizing radiation, microgravity, isolation and other spaceflight hazards pose significant risks to astronauts. Determining neurobiological and neurobehavioral responses, understanding physiological responses under Central Nervous System (CNS) control, and identifying putative mechanisms to inform countermeasure development are critically important to ensuring brain and behavioral health of crew on long duration missions. Here we provide a detailed and comprehensive review of the effects of spaceflight and of ground-based spaceflight analogs, including simulated weightlessness, social isolation, and ionizing radiation on humans and animals. Further, we discuss dietary and non-dietary countermeasures including artificial gravity and antioxidants, among others. Significant future work is needed to ensure that neural, sensorimotor, cognitive and other physiological functions are maintained during extended deep space missions to avoid potentially catastrophic health and safety outcomes.