Because there's no up or down in zero gravity, the way our brains calculate 3D space stops working. As it turns out, that can be problematic, with astronauts finding it hard to complete basic tasks. It's a phenomenon that NASA wants to learn more about, which is why the agency has started to test a crew's spacial awareness before, during and after their trips to space. Whilst on the ground, participants are subject to MRI scans, and on the ISS they're asked to complete various tests requiring thinking and co-ordination. The reason that this is so interesting isn't just because the testing is going on above us right now, but because of what conclusions have already been drawn.
For instance, researchers are increasingly certain that humans can't think as well in space as they can on a planet. In which case, Star Trek's idea of just beaming down to a strange new world was missing the bit where they struggled to stand up. In addition, any crew that's sent to Mars might have difficulty conducting emergency repair work after a landing, especially if they can't pick up a wrench. The study will also have real-world consequences, too, since people undergoing treatment for chemotherapy can suffer a similar reaction -- so it's not just astronauts who'll benefit from its findings.
[Image Credit: University of Michigan]