The workings of the hippocampus area of our brain are still mysterious to neuroscientists. This is the area of the brain that plays an important part in consolidating information in order to process it through the short-term and long-term memory.

What secrets lay behind the hippocampus? Does it have a visual map that lays out our thoughts like the streets on a road, or does it just place memories in a filing cabinet to retrieve them at will? Does the hippocampus navigate all our thoughts through different routes and then assigns them a place, or does it act like a traffic cop and direct them to where they need to turn? These are all questions that are still unanswered.

Friedrich Nietzsche once said, “The existence of forgetting has never been proved:  We only know that some things don’t come to mind when we want them.”

One researcher and her team think they may be able to answer at least some of these questions. Eleanor Maguire, Professor of Cognitive Neuroscience at the Wellcome Trust Centre for Neuroimaging at UC London conducted a study of bus and taxi drivers in London, tracking their brain waves through the hippocampus with the use of a functional MRI (fMRI) scanner.

What they found was that, although both sets of drivers navigated the London streets, taxi drivers utilized their hippocampus more, and even increased the size the longer they were on the job. The bus drivers, assigned to the same route all the time, did not.

Their next step was to find out how the hippocampus stored the information – either through a visual map or by recalling relationships between objects in a more generic way. To find the answer they used the fMRI again to trace which parts of the brains were active as the participants visually retraced the route between their friends’ houses, as compared to their relationship with the friend themselves. What they found was that the hippocampus was active when different locations were visualized, but not when they just were navigating their social network. Separate networks were active for each of these functions.

The researchers then looked at retired taxi drivers (Maguire said it was a difficult task because they never seem to retire.). They wanted to see if the hippocampus of the retired drivers would shrink back to normal levels once they stopped using the driving skills to navigate the 25,000 streets of London. They found that it did return to normal size when their driving jobs were done. This would indicate that that if you utilize your brain for a specific function requiring strategic thinking on different levels, your hippocampus will enlarge and grow in that area. When you cease to need it, it will return to its original size.

They also took their research a step further and studied a 40-year veteran of London’s taxi driver squad who had contracted a viral infection that damaged his hippocampus, causing amnesia. While he was able to navigate using major or ‘A’ roads, he was no longer able to navigate the side streets and winding minor roads of the capital. “That shows that the hippocampus is necessary for fine detailed spatial representation of the city,” says Maguire.

This brought about more questions, such as, “Do others with exceptional memory undergo similar changes in their hippocampus?” Maguire and her colleagues went on to the World Memory Championships in London and studied participants. “People entering the World Memory Championships can do amazing things,” Maguire explains. “They can memorize the order of cards in deck after deck of cards, for example. One memory champion passed time waiting in reception prior to his scan by memorizing pages from the phone book – pretty well, too; I tested him on it,” she said.

To the researchers amazement, they could not find structural changes like those of the taxi drivers. It seems that the memory feats in the championship did not put much demand on the hippocampus.

When asked what type of memory strategy they used, nine out of ten said they were using the “method of loci” strategy. Although method of loci utilizes spatial memory as the participant imagines himself going down a street, placing items into memory along certain streets or locations and retracing their steps to retrieve the item. It was much like a bus drivers route – and large-scale memorization was not necessary. “Their brain doesn’t have to change to accommodate a large map of London in their heads as it does for the cab drivers; the memory champions just need to memorize a couple of routes in detail,” Maguire said.

“Findings like those from our study of London cab drivers show that structural changes can occur in healthy human brains. Perhaps in the future we could use that kind of understanding to help people with hippocampal damage.” There are, of course, other circuits involved in memory as well. “When we use fMRI, other brain regions are engaged also. We still don’t know a great deal about what they are doing. Until we do, it won’t be possible to design a memory rehabilitation program with confidence,” Maguire says.

This study shows definitively that the hippocampus is essential to spatial thinking, and that portions of it are necessary to perform intricate tasks on a regular basis. It indicates that the hippocampus will grow as long as it is being used. 



About the author:

Ron White is a two-time U.S.A. Memory Champion and memory training expert. As a memory keynote speaker he travels the world to speak before large groups or small company seminars, demonstrating his memory skills and teaching others how to improve their memory, and how important a good memory is in all phases of your life.



Welcome Trust – Mapping Memories: Eleanor Maguire and Brain Mapping: