It has been suggested before that Sudoku number puzzles improve memory, while crosswords expand the vocabulary. The elderly are also said to benefit from a new generation of computer exercises played on video consoles to improve recall.

However, for the first time, scientists have proven that mental exercise really does limber up the brain and make it more quick-witted.

A Swiss-American team reports in a leading scientific journal how they used a computer based brain-training method to improve general problem-solving ability.

Many psychologists had thought the only way to improve this was actually by practising the specific problem solving task you wanted to get better at. However, this theory is overturned in the work by Drs Susanne Jaeggi, Martin Buschkühl and colleagues at the University of Michigan, Ann Arbor and University of Bern.

They say you can improve generally problem solving ability by carrying out unrelated mental exercises and puzzles.

In the experiment, the team gave 35 volunteers a series of mental training exercises designed to improve their working memory, while they also had 35 more subjects who did not undergo the "brain boot camp".

Those who underwent the mental exercise tests, were shown a sequence of squares appearing one after another on the computer screen every three seconds. The task was to decide whether a certain square was at the same position as another one previously seen in the sequence.

At the same time, participants heard spoken letters and had to decide whether the currently heard letter was the same as one presented two or three steps earlier in the sequence.

If they did well the task became harder, while if they did badly it became easier. They repeated the exercises for between eight and 19 days.

Their problem solving ability was then assessed compared to the group who had not taken part in the exercises.

According to the results of the study, published in the Proceedings of the National Academy of Sciences, the group who took part in the puzzles had a significantly improved problem solving ability. Moreover, the more the participants trained, the more problems they could solve.

Motivation however, was also important too - suggesting people have to be committed to mental exercise to reap the benefits.

Dr Jaeggi said: "It's the same in sports: you can not expect to get better in football if you merely run around a little bit and not really want to improve."

This is the first evidence that mental exercise improves intelligence and problem solving ability generally and suggests time spent on crosswords, Sudoko and other number and word games is time well spent.

By Roger Highfield, Science Editor

RESOURCE/SOURCE:  www.telegraph.co.uk on April 29, 2008