How the Brains of Taxi Drivers Throw New
Light on Dyslexia

The idea of a learning disability is deeply rooted in research studies demonstrating that the brains of people with learning difficulties, such as dyslexia, are different from the brains of so-called “normal” people. Such neurological differences, supposedly, are the cause of dyslexia or a learning difficulty.

More and more research studies, however, suggest that the cause-effect relationship should be reversed, i.e. that these differences might not the cause, but the effect of the reading or learning difficulty.

There is ample evidence in the literature to demonstrate that the structure and function of the brain are to a large extent determined by the way it is used and educated. By sacrificing their brains during controlled experiments, this is already known to be a proven fact in the animal kingdom. Mark Rosenzweig and his associates, for example, have shown that the brains of rats raised in an “enriched” laboratory environment — in a large cage containing many fellow rats and playthings that could be explored and manipulated — differed markedly in a number of respects from rats raised in small, isolated cages. The rats in the enriched environment had a greater weight and thickness of cerebral cortex than the ones raised in isolation. The researchers found more spines — which often serve as receivers in synaptic contacts — on the dendrites of cortical neurons in rats from enriched environments. Synaptic junctions in rats from enriched environments averaged about 50 percent larger than those in rats raised in isolation, and synaptic contacts were more frequent in the rats from enriched environments.

Of course, no conclusions on human learning or functioning can be drawn from experiments on animals, but it is nevertheless interesting to take note of such experiments, because they seem to confirm that stimulation does indeed change brain structure.

Furthermore, more and more researchers confirm that, in this respect, humans are no different from animals. In their book, Brain, Mind, and Behavior, Floyd E. Bloom, a neuropharmacologist, and Arlene Lazerson, a professional writer specializing in psychology, state, “Experience [learning] can cause physical modifications in the brain.” This is confirmed by Michael Merzenich of the University of San Francisco. His work on brain plasticity shows that, while areas of the brain are designated for specific purposes, brain cells and cortical maps do change in response to experience [learning].

A study in London has found that an area of the brain associated with navigation was larger in London's famed taxi drivers than in other people. The drivers' brains have been adapted to help them store a detailed mental map of the city, shrinking in one area to allow growth in another, according to the study.

Evidence that the brain is physically able to change according to the way it is used could have important implications for people with brain damage or brain diseases such as Alzheimer's, say experts. London taxi drivers are renowned for their encyclopedic knowledge of the capital's streets. They spend an average of two years learning the layout of the city's roads before taking a test to get their licenses. Scientists have also reported differences in the structure of the brain between musicians and non-musicians.

Recently, German researchers found that juggling increases the size of your brain. Arne May, neurologist at the University of Regensburg, and colleagues asked 12 people in their early 20s, most of them women, to learn a classic three-ball juggling trick over three months until they could sustain a performance for at least a minute. Another 12 were a control group who did not juggle. All the volunteers were given a brain scan with magnetic resonance imaging at the start of the program, and a second after three months. After this, the juggling group was told not to practice their skills at all for three months, and then a third scan was taken of all 24 volunteers.

The scans found that learning to juggle increased by about three percent the volume of gray matter in the mid-temporal area and left posterior intra-parietal sulcus, which are parts of the left hemisphere of the brain that process data from visual motion. Students who had not undergone juggling training showed no such change. After the third scan, by which time many recruits had forgotten how to juggle, the increases in gray matter had partly subsided.

“Our results contradict the traditionally held view that the anatomical structure of the adult human brain does not alter, except for changes in morphology caused by aging or pathological conditions,” their study says.

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