Brains and Brawn, One and the Same

January 25, 2004
By NICHOLAS WADE

IF you hit the weights at the gym with iron regularity, your arms may get to look a little more impressive. The right kind of training, it now appears, can do much the same for the brain, though unfortunately the enlargement can be shown off only to observers with magnetic resonance imaging machines.

In a study conducted by Dr. Arne May and colleagues at the University of Regensburg in Germany, people who spent three months learning to juggle showed enlargement of certain areas in the cerebral cortex, the thin sheet of nerve cells on the brain's surface where most higher thought processes seem to be handled. They were then asked to quit juggling completely, and three months later the enlarged areas of the cortex had started to shrink.

The finding, which was reported in the current issue of the journal Nature, is similar to one in a study of London cab drivers four years ago. Unlike their colleagues in New York, London cabbies must memorize the entirety of their city's streets. If some Sunday morning in London you should see a group of men on bicycles, maps balanced on the handlebars, those are apprentice cabbies, acquiring "the knowledge," as the two-year memorization of London's many small, winding streets is called. The 2000 study, also done with M.R.I. scanners, found a change in the shape of the cabbies' hippocampus, the brain module where new memories of place are stored.

Both studies show how malleable the brain is under training, a finding already hinted at by the brain's own internal representation, or mapping, of body parts. In monkeys trained to use their fingertips for some task, the areas of the brain devoted to mapping the fingertips will enlarge, suggesting that the brain's various maps of the body are "plastic," in the parlance of neurology, not hard-wired.

The M.R.I. scans of jugglers and cabbies showed an enlargement of the gray matter, the brain areas rich in neurons, as opposed to the white matter, which consists mostly of the biological wiring that connects neurons. But the scanning machines can't see down to the level of individual neurons, so it's unclear what is causing the enlargement. Whether new neurons are ever generated in the adult brain has been a matter of fierce contention, the present consensus being that new neurons are created in the hippocampus and olfactory bulb but nowhere else.

Dr. May said the enlargement in the jugglers' cortex could be caused by new cells, whether created at the site or recruited from other areas, or by new interconnections. He favors the interconnection idea, he said via e-mail. Pasko Rakic, a brain expert at Yale University, said the study was interesting and confirmed that the brain is not structurally static. But no conclusion can be drawn as to what may be going on at the cell level, Dr. Rakic said.

The brain has about 100 billion neurons, each of which makes on average 1,000 connections with others, for some 100 trillion interconnections in all, none of them color coded. Learning to juggle, or navigate London streets, must involve a horrendous rewiring job. But the brain's electricians seem to know what they are doing, and no doubt it's good to keep them exercised.