Sep 11 2008

London Taxi Drivers and the Brain’s Navigational System

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London, being an old city that developed its street plan long before cars were invented, and without any top-down planning, is a maze of 250,000 streets. London taxi drivers who have mastered this complex meshwork of byways over years were found to have greater than average hippocampus size. This built on earlier work showing that London taxi drivers activate their right hippocampus when recalling specific routes through London. (The right hemisphere is typically the one responsible for visuo-spacial memory and processing.)

Now a new study takes this research another step. From the press release:

In a follow-up study, Dr Spiers and Professor Maguire used the Playstation2 video game “The Getaway” to examine how taxi drivers use their hippocampus and other brain areas when they navigate. Taxi drivers used the virtual reality simulation to navigate the streets of London whilst lying in an fMRI brain scanner. The researchers found that the hippocampus is most active when the drivers first think about their route and plan ahead. By contrast, activity in a diverse network of other brain areas increases as they encounter road blocks, spot expected landmarks, look at the view and worry about the thoughts of their customers and other drivers.

Based upon this and other research the current model holds that there are three basic kinds of navigational brain cells in the hippocampus and other associated brain regions. These include place cells, which encode information on location – a specific place cell will fire when we are in a specific familiar location.

The second type are called head direction cells, which act as a compass. They encode information about direction. The third type are called grid cells. They remember how far we have traveled, as if through a grid.

Therefore, with these three kinds of cells our brains know where we are, which way we are headed, and how far we have traveled. Obviously these systems are imperfect and the information in them spotty – based largely on our experience.

The press release likened these location brain functions to a map with specific landmarks, a compass, and grid systems like latitude and longitude.  I think these analogies are apt, and in fact would take it one step further. It is possible that we developed these technologies specifically to work with the navigational systems in our brains. In other words – our brain structure and function determine how we think, and how we think determines the tools that we use and the way that we envision our world.

To give another example, modern video technology is largely based upon an RGB system – TV screens and monitors at the pixel level produce red, green, and blue colored pixels which combine to form all the colors that can be displayed. This system mirrors the red, green, and blue cones in the human retina – essentially using these three colors in combination to create all the colors our brains can see. The display technology works well because it mirrors the processing of our visual system.

Maps, landmarks, and grid systems work well because they mirror the exact ways in which our brains process navigational information.

There is also person-to-person differences in the relative strengths and weaknesses of these subsystems. In other words, some people navigate better by paying attention to landmarks and general direction, while others prefer to use grid-like strategies. Although most people use a combination of strategies based upon the situation and the information available.

As an example of this one study looked at a London taxi driver (what would neuroscientists have done without them) with bilateral hippocampal injury, but who had learned the streets of London long ago before the injury. They found that he was still able to navigate well, but relied on main arteries, and quickly became lost in side streets. It appears, perhaps, that using direction and grid information was retained, but he lacked the detailed landmark knowledge of the place cells in the hippocampus.

The London taxi driver studies also provide yet more evidence for the plasticity of the brain. By learning so many landmarks, experienced taxi drivers increased the number of place cells in their hippocampi, causes them to be measurably larger. The brain adapts by allocating resources to tasks that are used and practiced, while others will atrophy.

While not completely a zero-sum game (overall brain function can improve with use and atrophy with neglect) any significant increase in one brain region comes at the expense other, most often nearby, regions. Those cells have to come from somewhere. For example, while the posterior hippocampus increases in size in London taxi drivers, the anterior hippocamus is smaller than average, even though the entire hippocampus is larger.

Also – increase in the hippocampus appears to be specific to navigational skills – not other types of knowledge (which is a plausible alternative hypothesis since the hippocampus is involved with short-term memory). Studies of physicians (who have mastered a large fund of knowledge) and IQ-matched controls showed no change in hippocampal volume.

One other neat aspect of this research I would like to point out is the increasing use of video games to simulate navigation around London.  A detailed London street simulator exists to train taxi drivers, and this can be used to simulate driving around London. The simulator can also be switched from an overhead view to a first person street level view – representing different strategies for navigating.

I predict we will increasingly see these kinds of strategies employed in neuroscience research. Video games have several advantages. They can be completely controlled – all variables can be exquisitely controlled, and this is always desirable for research. They are convenient – fMRI scans and PET scans could be done while drivers were using the simulator and this would not have been possible while actually driving. And simulators can easily be used to provide different types of experiences, like navigating from an overhead perspective, that would not be possible or practical in the real world.

Virtual reality studies are also being used in various types of experiments – to simulate human interactions and social situations, for example. Early data suggests that the emotional and cognitive response to a virtual simulation can be similar to responses to the real world. As virtual reality technology improves it will become increasingly more useful as a psychological tool.

Imagine being able to run a psychological experiment with virtual reality, so that the environment and sequence of events is exactly replicated in each trial, with complete control over all variables.

In conclusion, this line of research seems to support the modular model of brain organization and function – that specific parts of the brain encode specific functions. But it also holds some support for the neural network model as well – that function is encoded in the network of connections among brain parts. While I think this tips the scales a bit toward the modular model, it really reinforces the conclusion that both models are true to some extent and a combination of modules and networks may be the best way to understand brain organization and function.

It also provides more evidence for what I have known my entire adult life – video games are cool.

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12 responses so far

12 Responses to “London Taxi Drivers and the Brain’s Navigational System”

  1. Blair Ton 11 Sep 2008 at 11:50 am

    I have read that men and women have noticeable differences in navigation techniques – that is, men are more likely to navigate using a gird system and women more likely to use landmarks.

    This certainly conforms to my own experience. I always navigate by thinking about where I am in relation to a north, east, west, south grid, so that I can get from one point to another from anywhere on the grid, even if I haven’t been there before. My wife seems to need to remember specific landmarks and will repeated ask me if I am sure if I know where I am going, if say, we are walking around a city when haven’t visited before.

    Are there any studies that support a sex difference? If so, are there any theories on why there would be a sex difference?

    Cheers,

    Blair

  2. deciuson 11 Sep 2008 at 1:52 pm

    Blair T

    Unless you have a compass or other navigational devices, your approach won’t work in London and in most European cities.
    As Steven pointed out, streets are not laid out in a grid according to modern urban planning.

  3. Fifion 11 Sep 2008 at 2:36 pm

    Can we hypothesize then that men are more likely to get lost in London and women in New York? ;-)

  4. Blair Ton 11 Sep 2008 at 4:31 pm

    decius,

    I was perhaps imprecise in my use of language. When I say using a grid I mean being aware of my orientation to the compass points on a map, which necessitates some use of landmarks to triangulate your position. Once you know where you are in relation to where you want to go you can make you way in the right direction, even if you have never traveled that route before.

    The other mode of navigation, that I think is more often attributed to women is the use of navigation markers for a particular route. That is, when we park our car somewhere, my wife will look back several times to try to remember particular landmarks on the route in order to find the car. I try to remember where the car is based on it location in a mental map in my head, so I don’t need to follow the same route back to it.

    Coincidentally, my wife and I were in Europe last year, and she seemed surprised that I could find my way through cities I had never been too before, including London. To give her her due though, when it came to figuring out the train system, I left it all in her more capable hands.

    Though I did not find London difficult to navigate, I must admit that I have gotten lost in sections of Madrid, Seville and Venice, even while I had a map in my hand! So, I take your point about some European cities.

    Fifi – sounds like there is a good experiment to be conducted there.

    Cheers

  5. Gibon 11 Sep 2008 at 4:55 pm

    As an ex-cabbie (not English) this is interesting.

    I wonder how they figured that the brain size changed when you became a cabbie, as opposed to the possibility that only people with already different brain sizes became cabbies…

    I suppose I’ll have to read the article… Horror!

  6. Gibon 11 Sep 2008 at 4:57 pm

    Steve,

    I wouldn’t be this pedantic (well, probably not), but seeing as it’s in the first sentence of the article, I thought I’d point out the correct form of “it’s” is actually “its” here……

    As in “London, being an old city that developed its street plan…”

  7. pipon 12 Sep 2008 at 9:36 am

    I’m a woman and I have no sense of direction – I have to navigate by landmarks even in very familiar cities.

    I wonder if the evolutionary explanation for this is the division of labour among our primitive ancestors – the women cared for the children and the ‘home’, the men were the hunters. So the women would presumably follow established pathways to the water hole, or the known ‘gathering’ grounds for fruits, nuts, firewood etc, while the men would have to go far afield on hunts, or forays against other tribes, or to find more productive locations to move to.

  8. Fifion 12 Sep 2008 at 1:47 pm

    pip – If we’re going to advance an evolutionary theory I’d suggest that since the women were the gatherers they’d actually be following the same paths day after day and year after year to where the various foods being gathered grow. It’s not that women have no navigational skills (or gay men for that matter) it’s just that they’re different than men’s (and gay women’s).

  9. CharlesGon 12 Sep 2008 at 5:39 pm

    The specific difficulties of the driver with hippocampal damage are very interesting; although the fact that he remembers the main thoroughfares but gets lost on sidestreets he used to know is very suggestive of the existence place-direction-grid cells, but it would be nice to be able to construct an experiment that specifically utilized landmarks rather than speculating on the difference between main and side streets. Perhaps giving directions in terms specifically of landmarks, rather than an address? I wonder if route planning activates the cells in the same way as active navigation.

    Meanwhile, of course, as we inch ever nearer to really understanding how different parts of brain work, some people are filling in the blanks with whatever they want. In India they’ve started convicting people of crimes based on brainscans:

    http://www.toptechnews.com/story.xhtml?story_id=030003EKTPMC

  10. eatbolton 12 Sep 2008 at 5:43 pm

    I work for a company that build large-scale immersive displays for research purposes. Things like inverted domes, reality caves, and chevron-shaped screens. These are employed by institutions like UCLA, University of North Carolina, MIT, CalTech, Plymouth, etc. These put playstation 2 graphics to shame and are much more immersive, but their expense is really an obstacle for most institutions to build them. It’s a shame because they are such good environments for research of the neurological variety.

  11. julieon 13 Sep 2008 at 4:59 am

    It almost seems like the controversy about ebonics. The theory was to acknowledge non standard, African American English dialect just to hightlight the differences between that and standard English. But that’s a strange way to spend time in a classroom when you focus on one specific way of being wrong. Here the proposed idea is to acknowledge one religious creation story just to point out how it doesn’t match the scientific version.

  12. kelon 15 Sep 2008 at 9:53 am

    I remember hearing from a lecturer that some Australian languages use absolute (east, west, north, south) instead of relative (left,right) spatial description, and this is also expressed in their gesture. For example, instead of asking someone to ‘move over to the left a little’ it would be ‘move to the east a little’ and gestures that accompany a storytelling will accurately reflective the spatial orientation of the object. So in effect, speakers of these languages are always aware of their own spatial orientation.
    I haven’t looked into it very closely, so I don’t know what studies have been done, but it would be interesting to see what kind of neurological differences exist between speakers of these languages and speakers of languages with more relative spatial description.

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