Free iPhone apps to strain your brain

We should probably start with a disclaimer here: Lumosity Brain Trainer is not really a free app. You can download it for free, and you can try it out for five sessions (one a day), after which Lumosity will ask you to subscribe for three, six or 12 months. That said, these puzzles — designed to improve attention span, memory and problem solving skills — are actually fun, in a challenging sort of way. Lumosity worked with neuroscientists to develop the app, so it does have some sort of science behind it; just be aware that, while this app calls itself "free", it's really only a trial version.

The N-back test is used by neurologists to stimulate brain activity while taking neuroimages. It presents the user with a sequence of sounds or images; the user then has to pick when sounds or images are being repeated at intervals. The dual N-back test simultaneously presents the user with a series of sounds and images, which they then have to remember independently. This is what IQ Boost Lite does. It gets pretty tricky, so make sure you check out the tutorial first, and it will give your brain a pretty serious stretching.

Sudoku is a puzzle that needs no introduction, and this app offers a four-level version of the game completely free. What we like about it is its lack of advertising and its easy, intuitive controls. It also auto-saves your game, so you can duck in and out as you like — handy if you have a five-minute bus ride or a few minutes to cool your jets while your pasta cooks. Unlike the previous apps on this list, Sudoku doesn't have any fancy-pants scientific backing, but doing maths in your spare time can only be a good thing.

Rush Hour Free presents you with a grid, with blocks (vehicles) taking up two or three squares. Your task is to move the blocks in such a way that the red block (car) has a clear path to the exit on the right-hand side of the screen. The closer you get to the minimum number of moves, the higher your score. It's a pure exercise in spatial problem-solving, with 35 games in four levels of difficulty — easy, medium, hard and expert. It also keeps track of your score and allows you to measure your skill up against other players.

The objective of Lumen Lite is to manipulate the lasers to shine on the checkpoints in the puzzle. There are mirrors that you'll need to line up, as well as colour filters that will change the colour of your lasers and other obstacles. It looks easy enough, but as you progress, the puzzles get more difficult. It has simple, bright graphics and a colour blind mode, with no timers to hurry you through solving the puzzles. The Lite version only has three levels, but the full version, if you like it enough to shell out two fitty, offers over 2100 puzzles.

This is only a short game, but it will really stretch your memory, lateral thinking and attention to small details. And, once you've finished the 61 levels in the game, you can earn trophies, look for hidden secrets, try to improve your best time and measure yourself against other players on the online leaderboard. OK, so it's not really much of a brain trainer, but all work and no play makes Jack a dull boy. We think William of Ockham would concur.