It takes more than an IQ to describe how our brains work Intelligence Quotient, or IQ, has been used to sort people, whether job candidates or schoolchildren, for decades. Now, a century after psychologists first came up with the idea of "general intelligence," the world's biggest study of its kind has put paid to the simplistic idea that we can use an IQ figure to describe the astonishing abilities of the human brain. Anecdotally, we all know people who are fantastic at speaking French, but poor at puzzles, or who can reel off telephone numbers from the top of their heads but are hopeless at maths. We also know that it would be absurd to use an "athletics quotient" to compare a long-distance runner with a sprinter. But in science you need hard evidence, and that is what we have managed to produce, with the help of 100,000-plus people - including many Daily Telegraph readers - who took part in the largest online intelligence test of its kind. Our attempt to find out whether intelligence can be reduced to IQ dates back more than five years, to when I was the science editor of this newspaper and encountered novel tests developed by Adrian Owen and Adam Hampshire at the Medical Research Council in Cambridge. They had devised a scientifically valid way to carry out cognitive tests online, to monitor rehabilitation after brain injury, the effect of smart drug trials and so on at home, rather than in the hospital. I asked them if we could use their tests to carry out a mass intelligence test for The Daily Telegraph. The challenges looked daunting, but Owen and Hampshire cracked it. What they came up with is emphatically not an alternative to the IQ test. They devised 12 tests that would trigger activity in as much of the brain as possible. So they knew that odd-one-out puzzles boost activity in areas at the front and top of the brain. I had a go, and I was impressed. It took half an hour to put a brain through its paces, and I can remember mentioning that I doubted more than a few hundred people would have a go. I need not have worried. When we launched the tests in October 2010 in The Daily Telegraph, Discovery and New Scientist, they went viral. In all, 110,000 people took part from every corner of the planet. We were so overwhelmed that the results were only published yesterday. Once Hampshire had sifted the million data points, we ended up with results from a representative group of around 45,000 people. Using a statistical tool to analyse the variations in performance, he found that they could be accounted for by three key factors: short-term memory; reasoning; and, finally, a verbal component. No single factor, or "Intelligence Quotient," could explain all the variations revealed by the tests. At the Brain and Mind Institute in London, where Owen and Hampshire now work, they studied what actually happened in the brains of those who took part. They scanned the brains of 16 participants and, to our satisfaction, found that each of the three different factors identified by the statistical analysis did indeed correspond to a different network: differences in cognitive ability map onto three distinct brain circuits. Each of these circuits contributes to that elusive quality we know as intelligence. The study, which the three of us co-authored in the journal Neuron, provided a wealth of insights into how factors such as age, gender and the tendency to play computer games influence our intelligence. Regular brain training didn't aid performance at all, yet people who often played other types of computer games did significantly better in terms of both reasoning and short-term memory. It seems the popular idea that brain-training games are helpful whereas standard computer games are somehow bad for us could be the wrong way around. We found that age diminished short-term memory and logical reasoning, with performance peaking in the late teens and declining rapidly thereafter. On the other hand, verbal intelligence held up well in the elderly. Some of the most interesting results were those where there was little relationship between lifestyle and intelligence. Physical exercise, weekly alcohol consumption, and the number of hours slept each night seemed to have negligible effects on performance. An interesting exception was the amount of cigarettes smoked. Forty-a-day puffers had significantly lower scores in terms both of short-term memory and verbal intelligence. Similarly, right or left-handedness, number of siblings and month of birth all made little impact. Gender, one of the most gleefully reported comparisons, showed little overall difference in performance, although men did do slightly better than women in terms of spatial short-term memory. We have now relaunched the test at cambridgebrainsciences.com/theIQchallenge to examine the influence of other factors on our capacity to think and to reason. We are not going to insult the intelligence of participants by talking about IQ when we report the results. The brain is a chemical machine containing in the order of 100 billion neurons and 100 trillion synapses. How could we think we could reduce the workings of the most complex known object in the universe to a solitary number? Roger Highfield is director of external affairs at the Science Museum Group