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.