The hippocampus is thought to be essential for navigation. Surprisingly, a paper published last year reported that a London Taxi driver, who suffered hippocampus damage on both sides of the brain, could successfully navigate around much of London.
London black cab drivers must pass ‘The Knowledge‘ to get a license.
It involves memorising London streets and being able to work out, from memory, the best route between any two places in the city.
In 2003, neuroscientist Dr Eleanor Maguire and her team won the Ig Nobel Prize (a humorous award for discoveries “that cannot, or should not, be reproduced”) for a study that found that the hippocampi of London Taxi drivers were larger than average, possibly because the drivers are constantly exercising their spatial memory.
Despite winning the Ig Nobel, this paper has been very important in understanding both spatial memory and how the brain grows during adult life.
The same team of researchers published a paper last year, looking at the navigation skills of a London taxi driver who suffered selective damage to both his hippocampi after a brain infection.
If the hippocampi were essential for navigation, it would be thought that such a person would have lost ‘The Knowledge’ or would be unable to use it in practice.
They tested the driver in a complete computer simulation of London (pictured left) and discovered, to their surprise, that he was surprisingly good at orienting himself in the city and navigating the main roads.
He often became lost, however, when he moved away from the main roads and had to rely on smaller roads for navigation.
This suggests that the hippocampus is necessary for the fine-grained knowledge of locations rather than navigation in total.
The researchers suggest that as roads become more familiar, they may become more like ‘semantic knowledge’ (facts like ‘Paris is the capital of France’) that you can remember without bringing to mind the context in which you learnt it, or last encountered it.
They note that the main roads may have become more familiar over time and so have acquired a more semantic-like status.
As this occurs, the information would become independent of the hippocampus, allowing the brain-injured taxi driver to keep some of his hard-won Knowledge.
Link to abstract of study on PubMed.