Cause for a rethink on how we learn

We learn a new word, or make a new friend, or taste a new dish, or undertake any of the innumerable things we do from day to day, and the experience is somehow etched into our brain and filed away in our mental world. If the experience is salient enough, it can be recalled again, even many years later, sometimes with amazing emotional vividness. It is the sum total of these personal experiences that makes each of us absolutely unique as individuals, since no one else could have had exactly the same experiences.

How does the brain do this? How does it take these bits and pieces of diverse experiences, and connect them together to build a coherent mental world?

When we recall an experience, often our language gets involved, with its nouns and verbs, syllables and intonations. But surely there isn't a miniature grammarian working away inside our brain, keeping a diary of our myriad activities, minute by minute. If there were, our inner grammarian would need another grammarian inside his brain to keep his diary, and so on ad infinitum.

So the brain must have its own distinctive language, nothing like the one you and I use. And obviously, being able to decipher the brain's language would have immense importance for our species, in particular for learning how we learn.

It is tempting to compare brains with computers, where any sound or image can be stored as long strings of ones and zeros. But that is only a very poor approximation of how the brain actually does things. The brain is vastly more complicated than any computer that has ever been built. We have only begun to study it scientifically since the start of the 20th century, when a Spanish doctor named Santiago Ramon y Cajal identified its most fundamental unit - the neuron.

According to the latest estimate, our brain has about 100 billion neurons, which communicate with each other across tiny spaces called synapses, not unlike switches in a digital circuit. Unlike digital circuits, however, the sender neuron releases tiny amounts of various chemicals into the synapses, called neurotransmitters, and these determine the behaviour of the receiver neurons.

On average, each neuron is linked to others by 1,000 synapses. So the amount of information that is constantly flowing in our brain is astronomically large. To support all this work, the brain is the most expensive part of our body, in terms of metabolic costs. Although modest in size, only 1.4kg or so, it draws about a fifth of the body's entire blood supply.

Numerous things happen when we learn a new word. Additional blood flows into the relevant regions of the brain. This raises the level of blood oxygen, which can be detected by the technology of magnetic resonance imaging, or MRI.

At the same time, the neurons chatter away with one another by sending pulses of electrical potential down their output arms, their axons. The changes in electrical potential can be monitored by electro-encephalography, or EEG. The magnetic fields generated by the flowing electrons can be measured by magneto-encephalography, or MEG.

Each of these powerful technologies of imaging the brain has its strengths and drawbacks. MRI pictures, constructed from three- dimensional scanning, are precise in locating the activity in space. EEG and MEG, on the other hand, are better in time resolution, in the order of milliseconds. These technologies were first developed for hospital use, but now they are increasingly harnessed for research on human cognition. Exciting windows are opening that allow us to view directly the source of our human uniqueness.

One early discovery, made at the University of California, Berkeley, several decades ago, was that relevant regions of the brain became enlarged with use. When mice were kept in 'enriched' environments, with companions and toys to play with, many cortical regions of their brains grew thicker than in mice kept in 'impoverished' environments. This lesson applies to human brains as well.

Recently, imaging studies have shown that the brain region that controls finger movement of the left hand is larger for professional violin players. More dramatically, a paper just published in the prestigious Proceedings of the National Academy of Sciences of the US by a group led by Lihai Tan of the University of Hong Kong showed that, with just two hours of training to learn four new words for naming colours, the visual cortex of the human subjects was significantly thickened.

Such enlargements of the brain cannot go on indefinitely, of course. At some point after the new skills have stabilised and integrated into the system, it appears that the neural circuits reorganise and the brain volume reduces. The situation is not unlike the evolution of computer technology, in which big and clumsy machines have been replaced by ever-smaller personal computers.

The brain of Albert Einstein is instructive. It has recently been studied in great detail. It turns out that, despite the scientist's extraordinary intellect, the various neuronal regions of his brain were of ordinary size. However, his brain had a much higher than average number of glia cells.

For more than a century now, ever since Cajal, it has been thought that it is the neurons that construct our mental world, with glia cells as silent partners that merely provide the metabolic infrastructure to serve the neurons. But some neuroscientists have begun to argue for a much bigger role for glia cells - that they interact with neuronal transmission in important ways, and even transmit information themselves by slow waves of chemical changes over longer distances.

An eloquent statement of their viewpoint is a book published last year by Douglas Fields of the US National Institutes of Health, titled The Other Brain. If they are right, then our understanding of how the brain constructs our mental world is in for some fundamental rethinking.

Therein lies the true excitement of basic research in science - we may be at the dawning of a new era of exploring the language of the brain.

William Wang, a linguist, is the Wei Lun Research Professor at the electronic engineering department of Chinese University

When mice were kept in 'enriched' environments with companions and toys, many cortical regions of their brains thickened

85%

The part of the brain's weight taken up by the cerebrum- most developed in humans, though elephant and whale brains are bigger