Our understanding of how the human brain performs mathematicalcalculations is far from complete. But in recent years there have been manyexciting scientific discoveries, some aided by new imaging techniques--whichallow us for the first time to watch the living mind at work--and others byingenious experiments conducted by researchers all over the world. There arestill perplexing mysteries--how, for instance, do idiot savants perform almostmiraculous mathematical feats?--but the picture is growing steadily clearer. InThe Number Sense, Stanislas Dehaene offers general readers a first look at theserecent stunning discoveries, in an enlightening exploration of the mathematicalmind.Dehaene, a mathematician turned cognitive neuropsychologist, begins withthe eye-opening discovery that animals--including rats, pigeons, raccoons, andchimpanzees--can perform simple mathematical calculations, and he describesingenious experiments that show that human infants also have a rudimentarynumber sense (American scientist Karen Wynn, for instance, using just a fewMickey Mouse toys and a small puppet theater, proved that five-month-old infantsalready have the ability to add and subtract). Further, Dehaene suggests thatthis rudimentary number sense is as basic to the way the brain understands theworld as our perception of color or of objects in space, and, like these otherabilities, our number sense is wired into the brain. But how then did the brainleap from this basic number ability to trigonometry, calculus, and beyond?Dehaene shows that it was the invention of symbolic systems of numerals thatstarted us on the climb to higher mathematics, and in a marvelous chapter hetraces the history of numbers, from early times when people indicated a numberby pointing to a part of their body (even today, in many societies in NewGuinea, the word for six is "wrist"), to early abstract numbers such as Romannumerals (chosen for the ease with which they could be carved into woodensticks), to modern numbers. On our way, we also discover many fascinating facts:for example, because Chinese names for numbers are so short, Chinese people canremember up to nine or ten digits at a time--English-speaking people can onlyremember seven.

Dehaene also explores the unique abilities of idiot savants andmathematical geniuses, asking what might explain their special mathematicaltalent. And we meet people whose minute brain lesions render their mathematicalability useless--one man, in fact, who is certain that two and two is three.Using modern imaging techniques (PET scans and MRI), Dehaene reveals exactlywhere in the brain numerical calculation takes place. But perhaps mostimportant, The Number Sense reaches many provocative conclusions that willintrigue anyone interested in mathematics or the mind. Dehaene argues, forinstance, that many of the difficulties that children face when learning math,and which may turn into a full-blown adult "innumeracy," stem from thearchitecture of our primate brain, which has not evolved for the purpose ofdoing mathematics. He also shows why the human brain does not work like acomputer, and that the physical world is not based on mathematics--rather,mathematics evolved to explain the physical world the way that the eye evolvedto provide sight.A truly fascinating look at the crossroads where numbers and neuronsintersect, The Number Sense offers an intriguing tour of how the structure ofthe brain shapes our mathematical abilities, and how our mathematics opens up awindow on the human mind.