To find the real brainiacs of London, you need not necessarily visit its hallowed universities, eminent Royal Society, or East London’s Tech City. Simply raise your hand and hail a cab. Your driver will know every street and landmark within a six-mile radius of Charing Cross train station—and he or she will possess an enhanced hippocampus to prove it, should you wish to run an MRI. Cabbies-in-training earn that extra brainpower during two to four years spent studying the streets. Their brains actually do grow during that time, according to the first longitudinal study of their prowess, published in the December 8 Current Biology by two other brainiacs at University College London.
First author Katharine Woollett and senior author Eleanor Maguire have been studying cabbies for more than a decade (reviewed in Woollett et al., 2009). The drivers make wonderful subjects for studying learning and memory in adults because London cabbie applicants must memorize 320 routes covering 25,000 streets and 20,000 landmarks (GPS is for wimps). This massive information set is called “The Knowledge.” Of those who try, only half succeed. (For comparison, New York City taxi drivers can qualify after courses of 24 or 80 hours.)
In cross-sectional studies, Woollett and Maguire found that cabbies have bigger posterior hippocampi than do control subjects (Maguire et al., 2000). The hippocampus controls spatial navigation (reviewed in Burgess et al., 2002) as well as episodic memory and future planning. While it could be that the job makes the brain, drivers might instead be self-selecting, with those who are naturals at navigation or who already possess a super-sized hippocampus going after the job. To test whether the training leads to the brain enhancement, the scientists recruited 79 men embarking on The Knowledge five years ago. The researchers performed MRI scans before and after training. Of those who stuck with the study, 39 passed the tests and 20 failed. A third, control group comprised 31 people who did not try to learn London’s layout.
Woollett and Maguire found no differences in hippocampal volume among the three groups at the first scan, nor between the first and last scan in controls or in trainees who did not make the grade. But for those who did succeed—who also put in twice as many hours studying as those who did not—their posterior hippocampi grew. Using voxel-based morphometry—a technique that divides the brain into small, defined regions—the authors found that MRI intensity in some voxels grew by as much as 50 percent between the first and second scan, only in applicants who qualified to be cabbies. “It is very compelling evidence that the adult brain can be changed,” said Kristin Flegal of the University of California, Davis, who was not involved in the study. “As we are beginning to learn more and more about neuroplasticity, it really challenges…the idea that the adult brain is fixed,” said Flegal, who coauthored a review on episodic memory plasticity in the December 8 Neuron.
What is the physical mechanism for the hippocampal changes? Scientists don’t know. The hippocampus is among the few brain areas that allow for new neurogenesis in adults, Maguire noted. “It is tempting to think that those new neurons might be recruited into the services of supporting this very detailed map of London,” she said. Then again, the physical change could be due to increased connections between the neurons that are already present, she added.
The work has implications for memory rehabilitation strategies, said Lynn Nadel of the University of Arizona in Tucson, who was not involved in the research. One might imagine, he said, that exercising the hippocampus could be useful for people with early Alzheimer’s disease or mild cognitive impairment, or those at high risk for AD such as ApoE4 carriers.
Brain training is already a growing industry, with websites and games offering puzzles supposed to strengthen the brains of the elderly (reviewed in Lustig et al., 2009). For example, Posit Science advertises the potential benefits of its brainteasers and word games. However, many of those programs remain unproven, Maguire said. As with her own work, to get proof, “longitudinal studies are the key here,” she said.
Studies performed so far indicate that episodic memory training improves skills on the specific task practiced, but does not necessarily translate to more general activities, according to Flegal’s review. Researchers obtained similar task-specific results with training in reasoning, memory, and mental processing (see ARF related news story on Willis et al., 2006 and ARF related news story on Owen et al., 2010). Another challenge is that, while it is possible to achieve transferrable benefits in the lab, the training tasks that researchers succeed with are dull. They are hard to translate into fun, engaging games, said Janine Jennings, who studies cognitive training at Wake Forest University in Winston-Salem, North Carolina. Jennings was not involved with the cabbie research.
The taxi driver studies also sound a note of caution about brain training, in that what bolsters one neural region might do so at the expense of another. As Woollett and Maguire found previously, successful cabbies were worse at recalling and drawing a complex sketch than failed trainees and control subjects. Maguire has also observed that established taxi drivers have smaller anterior hippocampi than normal, to go along with the larger posterior sections. The newly minted drivers did not exhibit this shrinkage, but Maguire suspects it might happen to them with time. Is hippocampal training a zero-sum game, then? “There is a bit of a price to pay for the expertise,” Maguire said.—Amber Dance
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