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Adult Brains Grow From Specialist Use
Xemu writes "Researchers at University College of London's Institute of Neurology have discovered that taxi drivers grow more brain cells in the area associated with memory. Dr Eleanor Maguire says, 'We believe the brain increased in gray matter volume because of the huge amount of data memorized.' She warns against the use of GPS and says it will possibly affect the brain changes seen in this study. This research is the first to show that the brains of adults can grow in response to specialist use." London cabbies, unlike their American counterparts, have to learn the layout of streets and the locations of thousands of places of interest in order to get a license.
See The Knowledge and the references from there. I think it is only required for taxicab drivers (ie "Black cabs"), not minicab drivers.
Studies were published in the year 2000. Why is this now getting attention? Actually, come to think of it, I think it got attention back then too.
Well, the reason they looked at London cab drivers is because of the massive amount of spatial information they have to know. The hippocampus was first shown to be involved in spatial memory in rats in the '70s (if memory serves), though it is also known to be involved in episodic memory.
The original idea was that the hippocampus holds a map of spatial environments, and so if someone has a very large amount of spatial knowledge, maybe their hippocampal anatomy will reflect that. This hypothesis is supported by this evidence (that lab has been doing these studies for years, not sure why this is claimed to be so new, except perhaps the control subjects who were bus drivers in London, reducing one potential confound). It should be noted that lately it has been shown that there is a very robust spatial code outside of the hippocampus (and feeding into it) so it appears to not be quite as simple as the hippocampus just holding a map.
Now to your questions. Names, stats, and details are semantic memory, not episodic memory, and are therefore not directly related to the hippocampus (except that all semantic memory appears to start off as episodic memorys, which are slowly re-coded, if you like, into just memory of the facts and not the specific episode where you learned the facts). So if you were constantly learning large amounts of new such data, perhaps you'd see such growth in the hippocampus, but merely having it all memorized would be relying on storage out in neocortex, not the hippocampus.
As the hippocampus (specifically the dentate gyrus, one part of it) is one of the few regions known to constantly be producing new cells, it is expected that experience might cause changes in size there. In other parts of cortex it would be more surprising (to me, at least) if there was a significant change in number of neurons. There the changes are more likely to be structural: neurons making new connections with other, existing neurons.
In summary:
hippocampus = spatial information and acquisition of new memories
neocortex = use and storage of existing knowledge