How would you describe your mental state at this precise moment? Alert, razor-sharp and crystal-clear? Or a tad foggy perhaps, struggling to remember the name of that ... actor who played ... Now what's his damn name ?... Just watched the DVD last week!

Sadly, as advancing years take their toll, many of us fall into the latter camp – unable to remember names and dates that we once plucked from the past with ease, and labouring over the easy Sudoku or the quick crossword. And age is not our only enemy: chronic stress, persistent overwork, a hectic and energy-draining lifestyle, the attention-span obliterating nature of quick-fire communications such as texting and Twitter – all conspire to make us feel frazzled and dull-witted.

This is merely irritating if it affects our performance at the office, or our ability to help with our kids' maths homework, but in the darker recesses of our (poorly functioning) brain we fear that it's just step one on the slippery slope towards dementia.

Over the last few years, a vast and hugely lucrative industry has sprung up, in part through an exploitation of this fear. We are promised that 'brain-training', with a little help from a £100 games console, will not only improve our memory and cognitive functioning now, but stave off dreaded, age-related conditions like Alzheimer's disease. In the vanguard of this brain-training revolution are Nintendo's "edutainment" programmes such as Big Brain Academy and Brain Training, which, the gaming giant claims, can actually boost blood flow to the brain and thus improve "practical intelligence" – and which are aimed at sharpening the minds of children as much as those of forgetful adults.

Nintendo also suggests that these products can make users "two to three times better in tests of memory" and that older people can keep their minds younger by using the console. On Nintendo's website, Japanese neuroscientist Ryuta Kawashima, who developed Brain Training, claims that "the more you use your brain in a challenging way, the better it can work". And with more than 90m of the Nintendo DS units sold worldwide, his message – endorsed by celebrities such as Nicole Kidman and Cheryl Cole – is clearly working.

Just one problem: a growing band of critics claim that this message is just another example of pseudo-scientific ad-speak. Last January, a study of 67 10-year-old children found no evidence to support Nintendo's claims. "The Nintendo DS is a technological jewel. As a game, it's fine," said Alain Lieury, a professor of cognitive psychology at the University of Rennes, Brittany, who conducted the survey. "But it would be charlatanism to claim that it's a scientific test."

Professor Lieury believes that grappling with that homework, reading, playing Scrabble or Sudoku, or watching documentaries instead of soap operas, matches or even beats the console as a brain-training strategy. In his study, he split the children into four groups. The first two groups did a seven-week memory course on a Nintendo DS, the third did puzzles with pencils and paper, and the fourth went to school as normal. Before and after, the children were set various tasks. The DS-using children showed no significant improvement in memory tests. They did do 19 per cent better in mathematics, but so did the pencil-and-paper group.

In a further blow to the claims of devices like the DS, a panel of experts – including eminent neuroscientists – last year stated that there was no evidence whatsoever that they helped improve memory or stave off conditions like dementia. These experts, employed by consumer group Which?, concluded that much of the evidence was "weak" and that other activities, such as playing standard computer games, could have the same effect. Crucially, none of the brain-training claims has been supported by peer-reviewed research published in a recognised scientific journal.

"If people enjoy using these games, then they should continue to do so – that's a no-brainer," said Martyn Hocking, editor of Which? magazine. "But if people are under the illusion that these devices are scientifically proven to keep their minds in shape, they need to think again."

So is brain-training just a big fat con, or are there concrete, scientifically proven strategies to improve mental function? According to the authors of a new book, The Rough Guide to Brain Training, there are – as long as you don't expect miracles. The book is co-written by Tom Stafford, a lecturer in psychology at the University of Sheffield, and puzzle maestro Dr Gareth Moore – whose Cambridge PhD in artificial intelligence suggests his brain is working reasonably well. It features 100 workouts, each containing old favourites like Sudoku as well as new puzzles. Regular tests break up the workouts and help you track your progress.

The book's credibility is enhanced by accompanying articles on brain-related matters, busting some oft-repeated myths and explaining what works and why.

"There are two incontestable facts with brain-training," says Stafford. "First, humans are amazing at getting better at anything they practice. We're the learning species – if you want to learn pi to a hundred digits in a weekend, or to memorise a deck of cards or master Ancient Greek, you can. Second, it's very hard to show that when you practice one thing you get better at another. The problem with all this brain-training stuff is that you might get better at doing puzzles, or remembering number sequences, but no one has found the Holy Grail of brain-training – 'far transfer', where you practice one thing and get better at an array of very different things."

This, according to the sceptics, is the fatal flaw with expensive brain-training gizmos: if you practice doing anything often enough, you will get better at it. This capacity to learn is what makes the human brain so miraculous. But if you gorge on, say crossword puzzles, although you will inevitably become more adept at completing them, there's no evidence to show that this will make you better at memorising historical dates, or doing long division.

There's also good evidence to show that the most effective brain-enhancing tools have a physical, social and emotional component. "One study in an old people's home found that the best tactics to stave off dementia were reading books, playing board games and musical instruments and taking dance lessons. Three of those are physical as well as mental," says Stafford.

This throws up another key point: the best exercise to keep your brain in tip-top condition is in fact physical, not mental. Kawashima's claim that a healthy supply of well-oxygenated blood to the brain is crucial for its function is accurate. When starved of oxygen, brain cells, quite literally, die. This is what happens when we suffer a stroke: the blood supply to the brain is stopped and neurons perish because they lack oxygen, resulting in paralysis or aphasia (loss of speech). "I freely admit that a book like this is not the best way to train your brain," says Stafford. "The best way to do that is through exercise – there's far better evidence to show that that will help your brain to function well than anything from the brain-training literature."

Sergio Della Salla, Professor of Human Cognitive Neuroscience at the University of Edinburgh, adds that our current obsession with quick fixes desires a simple, "magic bullet" solution like the electronic games. In fact, the answer is a multi-faceted one. "Rather than telling people to exercise a lot, have a healthy lifestyle, read books, keep up your sexual stimulation, go to movies, maintain a wide circle of friends with whom you engage in healthy debate, we are told that playing 10 minutes of Nintendo will turn us into Nicole Kidman," he comments wryly.

Rather dispiritingly, Della Salla – who speaks for pseudo-science busting charity Sense About Science – says that by far the biggest predictor of developing dementia is genetic ("so you should choose your parents wisely"). Maintaining physical fitness and mental sharpness may, at best, offer a slight protection for dementia and delay its onset or severity. "Even if you do everything you can, you might still get Alzheimer's disease, because diseases hit you sometimes, and diseases like Alzheimer's are pretty common," he says.

Rather than seeing brain-training as some miracle cure that increases our intelligence and cognitive functioning then protects these into old age, it's best to treat it like a gym workout. We do it because we enjoy it and can effect certain changes by performing certain exercises: building bigger pectorals through bench presses, for example. And that's how Tom Stafford recommends using his book.

"Puzzles are one of life's great pleasures, so just do them because they're fun," he says. "They will also help you learn what your mental strengths and weaknesses are and help you to get better at the things you're not so adept at. And that's far better than some brain-training regime sold to you by a snake-oil company taking advantage of your guilt about a lack of mental fitness."

'The Rough Guide Book of Brain Training' by Dr Gareth Moore and Tom Stafford, is on sale now, £6.99.

All in the mind: Myths about the brain

Omega-3 boosts brainpower

New research funded by the Medical Research Council and the Food Standards Agency has found that infant intelligence is more likely to be shaped by family environment than by the amount of omega 3 fatty acids, or DHA (docosahexaenoic acid), they consume in breast milk or fortified formula. Factors in the home, such as the mother's intelligence and what mental stimulation children receive, are far more important.

Drinking water makes you sharp

Although it's true that inadequate hydration has a detrimental effect on brain function, the oft-quoted idea that we need eight glasses of water a day to improve mental performance is a myth. Our bodies ensure that we are sufficiently hydrated by making us thirsty when we need to drink – and we get much of the water we need from food.

We only use 10 per cent of our brains