This article suggests that when you create new brain cells, it disrupts old memories. This thoroughly backs up my own experience. During revision for exams, I find that as I learn new things, the old things drop out of my head as quickly as I can fill it up.
To me, this seems to have a few consequences, the first couple of which I have written here. You can probably think of more.
-Brain training may be useful, but has the side-effect of destroying old memories.
-We should not spend time learning pointless information as it might replace important older information
More importantly, it also suggests that people are finally progressing in neuroscience research, and even drawing connections between the small-scale structure of the brain and its function.
Brains are cool and a mystery (James Bond is also "cool and a mystery", as is Mornington Crescent (the game))