A user's guide to how the brain functions

How can a blind climber 'see'? Will a machine ever outsmart the human mind? Is the internet making us more intelligent, or more stupid? David Eagleman, 'rock star' of neuroscience, has dedicated his life to finding the answers.

It ought to be quite intimidating, talking to David Eagleman. He is one of the world's leading neuroscientists, after all, known for his work on time perception, synaesthesia and the use of neurology in criminal justice. But as anyone who has read his best-selling books or listened to his TED talks on-line will know, he has a gift for communicating complicated ideas in an accessible and friendly way.

He lives in Houston, Texas, with his wife and their two-month-old baby. When we Skype each other, he is sitting in a book-lined study and he doesn't look as if his nights are being too disturbed by mewling. No bags under his eyes. In fact, with his sideburns and black polo shirt he looks much younger than his 41 years, positively boyish. His enthusiasm for his subject is boyish, too, as he warns me, he "speaks fast".

He sure does. And he waves his arms around. We are talking about the minute calibrations and almost instantaneous assessments the brain makes when members of the opposite sex meet, one of many brain-related subjects covered in his book Incognito: The Secret Lives of the Brain, which is about to be published in paperback.

"Men are consistently more attracted to women with dilated eyes," he says. "Because that corresponds with sexual excitement."

Still, I say, not exactly a romantic discovery, is it? How does this theory go down with his wife? 'Well she's a neuroscientist like me so we joke about it all the time, like when I grow a beard. Women will always say they don't like beards, but when you do the study it turns out they do, and the reason is it's a secondary sex characteristic that indicates sexual development, the thing that separates the men from the boys.'

Indeed, according to Eagleman, we mostly run on unconscious autopilot. Our neural systems have been carved by natural selection to solve problems that were faced by our ancestors. Which brings me to another of his books, Why The Net Matters. As the father of children who spend a great deal of their time on the internet, I want to know if he thinks it is changing their brains.

"It certainly is," he says, "especially in the way we seek information. When we were growing up it was all about 'just in case' information, the Battle of Hastings and so on. Now it is 'just in time' learning, where a kid looks something up online if he needs to know about it. This means kids today are becoming less good at memorising, but in other ways their method of learning is superior to ours because it targets neurotransmitters in the brain, ones that are related to curiosity, emotional salience and interactivity. So I think there might be some real advantages to where this is going. Kids are becoming faster at searching for information. When you or I read, our eyes scan down the page, but for a Generation-Y kid, their eyes will have a different set of movements, top, then side, then bottom and that is the layout of webpages."

In many ways Eagleman's current status as "the poster boy of science's most fashionable field" (as the neuroscientist was described in a recent New Yorker profile) seems entirely apt given his own upbringing. His mother was a biology teacher, his father a psychiatrist who was often called upon to evaluate insanity pleas. Yet Eagleman says he wasn't drawn to any of this. "Growing up, I didn't see my career path coming at all, because in tenth grade I always found biology gross, dissecting rats and frogs. But in college I started reading about the brain and then I found myself consuming anything I could on the subject. I became hooked."

Eagleman's mother has described him as an "unusual child". He wrote his first words at two, and at 12 he was explaining Einstein's theory of relativity to her. He also liked to ask for a list of 400 random objects then repeat them back from memory, in reverse order. At Rice University, Houston, he majored in electrical engineering, but then took a sabbatical, joined the Israeli army as a volunteer, spent a semester at Oxford studying political science and literature and finally moved to LA to try and become a stand up comedian. It didn't work out and so he returned to Rice, this time to study neurolinguistics. After this came his doctorate and his day job as a professor running a laboratory at Baylor College of Medicine, Houston (he does his book writing at night, doesn't have hobbies and has never owned a television).

I ask if he has encountered any snobbery within the scientific community for being an academic who has "dumbed down" by writing popular science books that spend months on the New York Times bestseller list? "I have to tell you, that was one of my concerns, and I can definitely find evidence of that. Online, people will sometimes say terrible things about me, but they are the exceptions that illustrate a more benevolent rule. I give talks on university campuses and the students there tell me they read my books because they synthesise large swathes of data in a readable way."

He actually thinks there is an advantage for scientists in making their work accessible to non-scientists. "I have many tens of thousands of neuroscience details in my head and the process of writing about them and trying to explain them to an eighth grader makes them become clearer in my own mind. It crystallises them."

I tell him that my copy of Incognito is heavily annotated and there is one passage where I have simply written a large exclamation mark. It concerns Eric Weihenmayer who, in 2001, became the first blind person to climb Mount Everest. Today he climbs with a grid of more than six hundred tiny electrodes in his mouth. This device allows him to see with his tongue. Although the tongue is normally a taste organ, its moisture and chemical environment make it a good brain-machine interface when a tingly electrode grid is laid on its surface. The grid translates a video input into patterns of electrical pulses, allowing the tongue to discern qualities usually ascribed to vision such as distance, shape, direction of movement and size.

I tell Eagleman I had to read that passage twice. "I know," he says, with a laugh. "It takes some believing. But the point is we see with the brain not the eye, and the brain generates expectations of what is out there. This is the topic of my next book which hopefully I will be finished in the next few months. It's called Live Wired and it's all about brain plasticity, how the brain changes and wraps itself around new input."

The blind Everest climber uses sensory substitution, but in his new book Eagleman will be exploring "sensory addition", which is where you give the brain all kinds of additional senses that have never been part of human experience before, including a perception of sensing the internet, or the stock market, or even weather data.

"Machines aren't able to behave like that," he explains, 'they have fixed circuitry that can break. But the human brain is like an alien material that adjusts its own circuitry to meet the demands of the task, so my new book is a call for this new generation of binary inspired machinery."

In Britain, interestingly, Eagleman is best known as a literary writer, specifically for his slim volume Sum: Tales From The Afterlives. It is a collection of short tales or, rather, "thought experiments" about the different possible afterlives. In one "story" people share the afterlife with all possible versions of themselves. In another you relive all your experiences, this time with the events shuffled into a new order: two months driving down the street in front of your house, five months flicking through magazines, six days clipping your nails and so on. It certainly gets the neurons firing and when Stephen Fry tweeted "You will not read a more dazzling book this year", shortly after publication, it became an instant bestseller.

One of the remarkable things about Sum (which Fry was right about, by the way) is that it reads like an extended prose poem. Not really what you expect from a scientist. Is it true he considered publishing it under a penname? "Yes.'" Why? "Two reasons: one was my science career, because I wanted to make sure it was separate. The second was that religious people might be offended by it. Equally I wondered whether my atheist friends would write me off as a proper scientist. But what happened, was that both atheists and religious people claimed the book for their own. The quotes on the jacket are from atheists, but there was a Christian website which awarded it a book of the year."

Eagleman calls himself neither religious nor atheist, I should point out, but a Possibilian, a denomination of his own invention, that, like the book, has attracted a cult following. "The idea with Possibilians is that we don't know what is going on here. It is a big, strange, lovely cosmos and if there's one thing that is clear it's that our ignorance of it is too vast to commit to atheism, and at the same time we know too much to commit to a particular religion."

If we get closer to understanding the human brain, will it help us understand the universe, I ask, not feeling entirely confident that my question makes any sense. "Boy, that seems right," he says. (Phew.) "What's happening in brain science at the moment is as exciting as the discoveries that are being made about the cosmos. Inner space and outer space. Maybe consciousness is a new kind of force, in the way electricity or magnetism is. It might be that, as we explore the brain, we come to an understanding of consciousness as being a separate property."

I tell him about a comedy song which the Irish comedian David O'Doherty performs called "very mild superpowers". When cycling with headphones on, O'Doherty can predict exactly where he'll be at the end of a song. He is also a very good judge of whether things fit through doorways, and which cupboard in a kitchen will have the crockery. I mention these examples because I know Eagleman has researched similar ones, examining why it is we know when our name is mentioned in a conversation that we didn't think we are listening to, or how we can have our foot halfway over the brake pedal before we realise that a red Toyota is backing out of driveway on the road ahead.

I also tell him that my own mild superpower is that I can often turn straight away to a reference I'm looking for in a book I've read, even if it is years after reading it, knowing whether it will be in the front, the back, on the left or right hand page, and at the top or bottom. What's going on?

"I have that, too," he says. "And I think it's down to the way we are naturally geographic. We store things by location. Even if you have a messy desk you can always put your hand on the thing you're after. I think this can also apply to the pages of a book where you have a sense of its storyline or architecture - being able to picture the thing on the page is like being able to picture the thing on the desk. Some people think of time in a very spatial way, too. They have a perfect autobiographical memory and can remember what happened any day of their lives. The reason is that each day for them has a geographical layout. This was how the Greek bards remembered poems such as the Odyssey or the Iliad. They would see it in terms of spacial locations."

Well fancy that. Feeling pleased about having my very mild superpower explained to me I realise we have run out of time - "that rubbery thing", as Eagleman calls it. He is fascinating on the perception of time, I should add, but we will have to leave that topic for another, ahem, time - because unlike the cosmos, we have run out of space.