Study on muscle action and lymph flow that indicates this is well established in multiple studies and indicates 3-6 x faster clearance with activity, though I have seen higher numbers elsewhere and, to my surprise, cannot readily locate that info at the momemt:

http://onlinelibrary.wiley.com/doi/10.1111/j.1469-7793.1997....

I am unaware of any papers on the piece I described as anecdotal and my opinion. Though a quick Google gets me this piece that claims it is by an MD and, among other things, talks about exercise and brain health:

http://jonlieffmd.com/blog/the-five-secrets-of-brain-health