Vestibular effects on other body systems
In vertebrates, the vestibular system and the otolith organs achieve spatial orientation and postural equilibrium. Recent evidence underscores the involvement of the vestibular system in the regulation of the circadian, respiratory and cardiovascular systems, food intake as well as bone mineralisation. Vestibular dysfunction can lead to pathological conditions such as orthostatic hypotension and sleep disruption. Apart from clinical ramifications, studying the biology of the vestibular system may prove beneficial for space exploration. The EU-funded SVETA (Vestibular system, cognition and vegetative regulations) project set out to establish an international cooperation with research centres that offer specialised facilities for studying gravitational physiology. Their activities focused on the effect of short-term vestibular stimulation on cardiovascular and brain functions, as well as the impact of vestibular loss or hyper-stimulation. Results showed that when subjects were submitted to ambiguous movements, such as tilt or translation, they exhibited different cardiovascular responses for the same vestibular stimulation. To understand the transmission of vestibular information, the research teams explored the connections between the vestibular inner ear and the hippocampus. As a result, they identified the associated neural pathways. Bilateral vestibular loss in rats led to spatial learning impairment as well as a disruption in the daily rhythms of temperature and locomotor activity. However, these effects and bone density were compensated with time. Furthermore, scientists investigated whether abnormal sensory integration could disrupt autonomic functions. In this context, they characterised the effects of two procedures known to disrupt cardiovascular regulation namely head down bed rest (HDBR) and dry immersion (DI). They observed that both HDBR and DI altered peripheral and central processing of vestibular information. This in turn had an impact on cardiovascular regulation. Collectively, the findings of the study support the hypothesis that the vestibular system has an influence on cognitive and autonomous functions. This association may partly explain the harmful effects of long-term weightlessness observed in astronauts and opens new areas of research in vestibular pathologies.
Keywords
Vestibular system, otolith organs, HDBR, DI, cardiovascular regulation