My current job is Associate Clinical Professor of Psychiatry at Harvard Medical School. That is my title - but my job really is a mission that I have been on for the past five years: to bring about more exercise and play in our children's lives.

I have travelled the world, talking with teachers, administrators, legislators, governors, presidents of countries, and the like. Initially, this was a hard pull, but it is beginning to take traction.

I have been at the head of teaching people about Attention Deficit Disorder (ADD), along with Ned Hallowell, my writing partner for three books on ADD. We have brought this important condition to the attention of the world.

I have been what I call a research synthesiser of neuroscience, trying to translate this for the layman as well.

There has been an increasing awareness of ADD, partly fed by my book in 1993 with Dr Hallowell, Driven to Distraction, which opened the door to everyone's being aware of ADD.

I think the whole issue is that many kids are over-treated, and many kids are under-treated. They have been arguing about this for many years.

Yes, people talk about having kids on medicine, and the significant issues there may be in changing their brain or certainly changing their labelling. But what about the opposite: where kids are failures and depressed, and get into substance abuse or worse? The ravage of depression on the brain is great. Not filling one's potential is even greater.

I came to write Spark* because I have always been interested in the effect of exercise on activity of the brain. I could see how important exercise was for many of my patients, especially to ward off depression and to help control their problems with attention and mood. I had outlined the book in 1995, but began to really pour into it when I noticed the school in Naperville, Illinois.

What caught my attention is that three per cent of their children were overweight, when the national average in the United States was 33 per cent. They had also finished number one in the world in science, and number six in math, in an international math-and-science test where all the countries in the world competed. This was quite incredible, and propelled me to begin writing.

My findings are that exercise is probably the most important way that we can regulate our emotions, as well as optimise our cognitive apparatus.

Yes, exercise can wear out your joints if you do it inappropriately. Now, even with runners, we are talking about using various thin-soled shoes or barefoot running. Because this helps you do the proper running which is a forefront strike as opposed to a heel strike. We are getting smarter. Here at Harvard the whole revolution started.

Does regular exercise make you live a longer life? Yes, of course, from your body's perspective as well as from your brain's. If you start exercising in middle age, you will push back cognitive decline by ten or fifteen years. Several Alzheimer groups say that, if you start exercising and continue three to four times a week, you will cut your risk of Alzheimer's disease in half.

Many schools throughout the United States and Canada have adopted Spark, some as a basis for their programmes. We have a group of people who are devoted to helping schools change. I have three Ph.D students working with me currently, to go in and educate the faculty, administration, and parents of schools that are interested.

Other countries have bought into this. President Ma Ying-jeou of Taiwan read the book some years ago, and had me come over and lecture at 11 universities. He immediately increased physical education time in his schools from two hours to three hours a week, and directed that my book be translated for younger people, elementary school-age kids, and now that is being done in Taiwan: 40,000 copies have been ordered by the government to distribute so that, early in their lives, children can begin to understand the benefits of exercise and play.

I grew up being a tennis player - a nationally ranked one - but now I'm a gym rat.

If you are good at games, you could, if you were also interested in being a brain box, be a better brain box. This is true for many reasons. We know that being fit improves your intellectual capacity as well as your emotional regulation.

OTHER STORIES

Interview: Brice Avery, psychiatrist, psychotherapist, writer

'I've been involved in clergy selection conferences for about 15 years. It's hard to assess someone's vocation and suitability for training. I try to help the archdeacons of the future by spotting the folk who will cause them sleepless nights in 15 years' time.'

You British call it sport. We call it exercise. Sport means athletics and competition, and that is one form of exercise. It's the most common form, perhaps, certainly the most public form. In the United States, we are looking more at exercise as an everyday thing for people. That is the ideal: to make people everyday athletes.

Exercise is not just taking a stroll, but pushing your heart rate up, pushing yourself, exerting yourself, getting out of breath, and sweating.

It has components of athletics: putting your mind to it and pushing beyond yourself. Certainly, there's "muscular Christianity". St Paul was an example of someone who really was striving. He had to strive against his own self and against others, and that is what you have to do when you exercise: push yourself beyond.

I have always been a "small r" religious person, raised in the "big R" religion: Catholic school, and so on. However, after college it was the "small r", meaning I was religious without an affiliation. My religion is the belief in humankind's possibilities, and a very firm belief that a purposeful, driven life toward helping others is much more important than any "big R" affiliation.

Of course I'll be watching the Olympics. I will be interested in gymnastics, track and field, soccer (my favourite sport), and a variety of others.

I am divorced, and have two grown and "launched" children, meaning that they are on their own, with their own lives and their own health insurance. Katherine is 29, soon to be 30, and Jessie is 31, soon to be 32. Jessie is married and works with a non-profit-making organisation, and Catherine works as a social worker with juvenile delinquents in the inner-city of Boston. Two failed marriages I would say are my biggest regrets.

I grew up in the steel-mill belt, and my big ambition was for everyone to get out of the steel mills and to get a college education. My siblings and I were the first to get a college education in our families. Both of my parents went only to the seventh or eighth grade, if that.

I think without a doubt the most important choice I made was to become an MD rather than a Ph.D., because this has allowed me to really get much more involved with patients quicker, and has allowed me a range of opportunity to do research, as well as to learn more about people and myself along the way.

I'd like to be remembered for helping change the world. We have done this with our work in ADD. Now I'm helping to change the way people look at exercise and play, realising that it is an important component of our lives. The Greeks knew that one cannot just be nurturing the mind; one has to also work on the body to have a chance at being a complete and perfect human being.

Easily the most important person for me was Dostoevsky. In my junior year in high school, I read Crime and Punishment, and it changed my life and made me much more interested in philosophy. I studied philosophy and literature, which I devoured passionately for the next chapters of my life.

I remember a sermon given in college by the Head of our Philosophy Department (he was also a Professor of Religion), talking about forgiving and forgetting, and the differences between them. That is something that I have used a lot in my work.

My favourite place is Tuscany. It used to be Florence, but now Florence has gone the way of most euro-bound places, and it's not as nearly as quaint as it used to be.

My favourite part of the Bible is the Old Testament in general, and the book of Job and the Psalms in particular.

The split between the rich and poor, which is only getting bigger and bigger - this is something that really makes me angry.

I'm happiest when I am fully engaged in whatever I am doing.

I do not pray on a regular basis. I think thoughts a lot, especially when people are in need. I try to send good karma to people that are struggling, friends of mine, people that have lost someone or who are in a bad way physically or otherwise.

It is hard to find real true hope, because the one area, of course, that we all look to is the development of science and technology, and it is the same thing that is killing us.

I guess I would like to have a conversation in church with William Shakespeare, and find out how this man was able to do what he did.

Professor Ratey was talking to Terence Handley MacMath.

*Spark: The revolutionary new science of exercise and the brain (Little, Brown, 2008).