I have heard that "90% of information flow in the brain (or maybe it was just the visual cortex) is top-down". I'm not sure if this claim is substantiated, but I do get the impression that there is strong evidence that at least most of the information flow is top-down. I'd like to know as specifically as possible what current theories in neuroscience say is going on here. I'd appreciate details and reputable academic works.
No the brain doesn't in practice work in a single flow. It takes a combination of top-down and bottom-up at various frequencies to perform any task. Outside a laboratory the amount of time you spend going top-down or bottom-up will depend on what kind of life you lead.