It was 15 per cent wider than that of people of normal intelligence, owing to extra development in what is known as the inferior parietal region. The findings are the first to suggest geniuses may have physically different brains.
Einstein, who died in 1955, insisted his brain be used for research. It was preserved but until now there had been no study of its anatomy. Canadian researchers have measured it and compared it with those of 35 men and 50 women of normal intelligence.
It was similar to the others except for the inferior parietal region. As a result of its extensive development, Einstein's brain was 1cm wider. The researchers, writing in The Lancet, say this may explain why he tackled problems the way he did: "Einstein's own description of his scientific thinking was that `words do not seem to play any role' but there is `associative play' of `more or less clear images' of a `visual and muscular type'.
Arguments about the biological basis of intelligence are unresolved, but with better measurement techniques and greater knowledge of the functions of parts of the brain, the researchers found a unique feature in Einstein's: the absence of a groove, called a sulcus, through part of the parietal region.
They think it may have allowed more neurons in this area to establish connections and work together more easily, creating an "extraordinarily large expanse of highly integrated cortex within a functional area". In other words, where the rest of us have sparks, Einstein had fireworks.