In class, we learned about the biology of memory and the parts of the brain responsible for certain memories. Explicit memories are largely processed by the hippocampus, while the implicit memories are taken care of by the cerebellum. Focusing on the hippocampus, we learned that it is involved in spatial memory as well, and forming declarative memories relies largely on the hippocampus. For example, H.M., a famous patient who had his hippocampus removed, found himself unable to form declarative memories. Multiple studies have shown just how crucial the hippocampus is to encoding memory.
Hippocampus in the human brain.
However, after looking into articles, there are indeed areas of the hippocampus that expand for London taxi drivers due to the rigorous testing of city routes to get the job in the first place and the constant need to learn routes in the labyrinth of London streets. According to an MRI study, more experienced taxi drivers had a larger posterior hippocampus than newer drivers, and the posterior hippocampus was larger in taxi drivers than control subjects. Furthermore, taxi drivers actually had smaller frontal hippocampi, suggesting a slightly different function between these two areas. Overall, I found it amazing that brain structure could change due to the stimulus of learning so many navigation routes. Although correlation is not equal to causation, this links the enlargement of the posterior hippocampus with the extensive memory London taxi drivers must possess.
Data from the MRI study of London taxi driver brains. The top shows how hippocampus size was determined via MRI. In the graph, the correlation between time spent as a taxi driver and the size of the posterior hippocampus is shown.
Interestingly, one article I read also revealed how taxi drivers encode street names into long-term memory, giving semantic meanings to otherwise arbitrary street names. Malcolm Linskey, a manager at a London taxi school, says tricks such as using phrases helps encode names of landmarks. For instance, “little apples grow quickly” corresponds with Lyric, Apollo, Gielgud, Queen’s, giving the order of theaters on a specific street. This is similar to what we heard in class about memorizing digit span by giving meaning to chunks of numbers.
Overall, the phenomenon of London taxi drivers with increased brain growth reinforces what we learned about the role of the hippocampus in explicit memory. Also, London taxi drivers also attribute their success in learning the navigation of London through encoding memory into long-term memory via meaningful linking, tapping into the unlimited storage potential of long-term memory.
References
Maguire EA, Gadian DG, Johnsrude IS, Good CD, Ashburner J, Frackowiak RS, Frith“Navigation-related structural change in the hippocampi of taxi drivers.”Proceedings of the National Academy of Sciences of the United States of America. 97. 4398-403. 10.1073/pnas.070039597.
Neurosci. “Know Your Brain: Hippocampus.” Neuroscientifically Challenged, Neuroscientifically Challenged, 26 May 2014, www.neuroscientificallychallenged.com/blog/2014/5/23/know-your-brain-hippocampus.
“Science/Nature | Taxi Drivers’ Brains ‘Grow’ on the Job.” BBC News, BBC, 14 Mar. 2000, news.bbc.co.uk/2/hi/677048.stm.