The brain is the essence of who we are. It is the prime mover; all of our thoughts and actions stem from it, and it becomes, in time, the unique blueprint of our personalities and experience. But it is, after all, a physical thing. Brain cells – and their connections – are just as susceptible to the ageing process as a heart or hip.

"When we talk about the brain getting older, it's not as though we're talking about wrinkles. A mature brain is a good thing", says Baroness Susan Greenfield, one of Britain's leading neuroscientists. "The brain synapses - the connections between one cell and another - are constantly being updated throughout your life, changing and getting stronger. The problem occurs when these connections stop working".

The most common indication of the brain ageing in this manner is the development of dementia (memory loss). As we live longer, conditions such as Alzheimer’s and Parkinson’s Disease are becoming increasingly common. According to the Alzheimer’s Society, 750,000 people in the UK have dementia and that number is expected to rise to 1.5 million by 2050. "We're all going to get [Alzheimer’s] if we don't do something to protect our brains" says Gary Small, the director of the Centre on Ageing at the University of California, Los Angeles.

Some of it is just luck of the draw. About 20 per cent of the British population is born with a gene called Apoe 4, which significantly increases the risk of developing Alzheimer's. But about two thirds of the risk is thought to be due to environmental factors. Some communities - such as the Mount Athos monks in Greece - have almost no record of dementia or stokes, and this is attributed to their stress-free lifestyle and diet.

Various processes can contribute to severe memory loss. In one, the blood vessels in our brains begin to stiffen up, a process accelerated by high blood pressure, This impairs the flow of blood around the brain and prevents blood carrying precious oxygen from surmounting the capillary walls to nourish the brain cells that need it. Another process, not yet fully understood, involves a disproportionate accumulation of amyloid - a fragment of protein involved in memory retention - on brain cells. There is some evidence to suggest that most Alzheimer's sufferers have had a least one minor stroke in their lifetime. Since a small amount of bleeding can occur in the brain without the person noticing, it is difficult to be certain.

Although Alzheimer's becomes much more prevalent after the age of 80, scientists believe the deterioration starts much earlier, in our forties. "You get a slowness of retrieval, the tip-of-the-tongue phenomenon", says Small. Soon dead brain cells and plaque start showing up on scans. The most important measures we can take are preventative and well in advance.

Greenfield advocates a special brain diet. The antioxidants found in foods such as berries, blackberries, broccoli and prunes fight off the free radicals that destroy cell walls. "As we age our own natural defence systems become less efficient, so we have to help them". Fish oils with omega-3 fats, and vitamin E and C supplements can also help, and folic acid is thought to reduce the risk of cardio-vascular problems such as a stroke. We should watch our fat and alcohol intake to maintain low blood pressure and reduce the strain on the heart.

The importance of physical exercise where the brain is concerned cannot be underestimated. Not only does obesity go hand in hand with high blood pressure, but there is evidence that exercise can actually make our brains stronger, since the increased blood flow to the brain brings with it more oxygen and glucose. A recent study by Fred Gage - a professor at the Laboratory of Genetics at the Salk Institute in California - showed that rats using a treadmill grow more brain cells than those that don't. Working out can actually create new brain cells.

Most important of all, says Greenfield, is stretching the brain itself. "Your brain is like a muscle - the more you exercise different connections, the stronger they will be". There are numerous gadgets on sale to test mental agility but they should be combined with regular simple exercises to help stave off memory loss - a crossword, or Su Doku puzzle, for example. "My own personal favourite is learning a new language, because you can always keep improving it and seeing the risk in your skills keeps it interesting", says Greenfield. It's important to pick something you enjoy. "If you're constantly worrying about the fact that you haven't done your exercises you're going to be in an inappropriate mindset". It helps to pay attention in the first place. Focus more on what a person looks like or is saying to you at the time and you will be less likely to forget it.

You might ask, in a generation used to predictions of computers more powerful than humans, whether we even need to maintain our brains. Surely mental agility will soon be improved with the aid of technological advances that defy physical deterioration. That, argues Greenfield, is missing the point. We need to maintain our ability to imagine and invent, as well as simply retain memories and control of our bodies: "The human brain isn't very good at computation. But it is good at having insight, at writing symphonies and novels, having a sense of humour. I don't see computers doing any of those things".

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