Do our brains change? Teenagers and taxi drivers provide the evidence.

Until a couple of years ago, conventional scientific wisdom held that after the few years of our lives, the structure of our brains is fixed. However two recent studies have cast doubt on these long-standing assumptions.

The first of these shows that the brain continues to develop throughout adolescence. It has long been known that babies experience neural development, but now Jay Giedd at the National Institute of Mental Health in Maryland, has shown that a spurt in the growth of connections between neurons also occurs in teenagers after the brain has reached its full size, with the peak occurring a year earlier in girls than in boys. By mapping over a thousand brains, Giedd found that the brain development was concentrated on the prefrontal cortex, the part of the brain responsible for planning and emotional control, providing a possible explanation for teenage moodiness and similar behaviour during puberty. Giedd also claims that, unlike in early childhood, the adolescent neural development is influenced by the person’s activities rather than genetics. So, in a sense, our brains are ‘hardwired’ during the teenage years, making them a critical time to optimise the brain.

Meanwhile, structural changes in the hippocampus, the region of the brain associated with navigational ability and spatial memory, of London taxi drivers have been observed. Researchers led by Eleanor Maguire at University College London have used magnetic resonance imaging (MRI) to show that although the hippocampus remains the same size in the drivers, the back part is larger while the front part has shrunk. The team compared the scans of 16 taxi drivers with those of non-cabbies, and discovered a link between the number of years spent as a taxi driver and the change in the right hippocampus, suggesting that experience rather than just some preexisting ability was responsible. Previous research has already shown that activity in the back of the hippocampus of taxi drivers increased as the drivers figured out routes around the city. Cabbies in London are particularly good subjects for such experiments as they are required by law to pass ‘The Knowledge’, a notoriously difficult test on the best routes around the capital requiring on average two years of preparation.

Why men may in general be better navigators than women

Past research has shown that men are in general better at navigating in unfamiliar settings than women. It is also known that women rely mostly on landmarks whereas men tend to use spatial geometry to figure out their way. But now there is biological support for these findings. Neurologist Matthias Riepe at the University of Ulm in Germany has scanned the brains of twelve men and twelve women trying to escape a three-dimensional virtual reality maze. The men got out of the maze in an average of two minutes and 22 seconds, compared with an average of three minutes and 16 seconds for the women. The difference is strategies was reflected by the brain activity of the two sexes during the exercise. Whilst both men and women used right hippocampus in negotiating the maze, only the men used the left hippocampus. Conversely, unlike the men, women used outer parts of the brain called the right prefrontal cortex and the right parietal cortex. Similar differences have also been observed in rats, suggesting that it may be biology rather than experience which is responsible.

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