Effect of altered gravity on the neurobiology of fish

In vertebrates (including humans) altered gravitational environments such a s weightlessness can induce malfunction of the inner ears due to a mismatch between canal and statolith afferents. This leads to an illusionary tilt b ecause the inputs from the inner ear are not confirmed by the other sensory organs, which then results in intersensory conflict. Vertebrates in orbit therefore face severe orientation problems. In humans the intersensory conf lict may additionally lead to a malaise commonly referred to as space motio n sickness (SMS). After the initial days of weightlessness the orientation problems (and SMS) disappear as the brain develops a new interpretation of the available sensory data. The present contribution reviews the neurobiolo gical responses, particularly those of fish, observed under altered gravita tional states concerning behavior and neuroplastic reactivities. Investigat ions employing microgravity (spaceflight, parabolic aircraft flights, clino stat) and hypergravity (laboratory centrifuges as ground-based research too ls) provide insights for understanding the basic phenomena, many of which r emain only incompletely explained.