Do you have trouble concentrating? Do you forget where you put your keys; have difficulty recalling words; find it hard to remember names? If so, join the club. We all have problems with memory and cognitive acuity. But as we age, these problems can increase, and some app developers have stepped in to help us train our brains. These companies--which use words like "neuroplasticity" to discuss the science behind these apps--claim that you can "improve your brain health," "improve focus, speaking skills, processing speed, memory, math skills," and "train memory, attention, and more." 

A word of caution: publications like Nature and Scientific American are skeptical of these claims, and a BBC study of 13,000 people showed that these apps don't really have any benefits. Despite that, many people find these games fun--if they just might keep your brain nimble, why not try them out? Here are a few to check out. 

Elevate 

Like all of these apps, Elevate for iPhone and iPad is free to play with in-app purchases. With the free version, you get to play a few games and try them out. Over time, you unlock more games, or you can get full access to 25 games for $5 a month or $45 a year.

Elevate's games seem a bit simplistic, with playful graphics and limited difficulty, as compared to, say, Lumosity or Fit Brains. But the games are interesting enough to use them as a first taste for this kind of app. The results are also simple; whereas Fit Brains shows you your results as a percentile of all users, Elevate merely shows you your high score, and some other vague stats.

Fit Brains 

Fit Brains Trainer for iPhone and iPad is also free to start using, but has a byzantine system of subscription pricing. The plus side is that it has a ton of games that train specific functions such as memory, logic, or language, and you can also play on Fit Brains Trainer's website. 

Some of the games remind me of when I was prepping for my SATs (a long time ago) and some seem a bit simplistic, as is the case with all these apps. Fit Brains is big on showing you how you stack up against others, and that, more than any score, is probably a good metric for whether you are good in a specific area (such as focus, problem solving, language, etc.), and can help show you what areas need work.

There are a number of games you can play for free, and a pro version gives you access to more games, and, for the full-monty subscription, other apps as well. But the company's aggressive marketing is annoying; they regularly send you emails offering you time-limited discounts. If you do plan to upgrade, wait a while and save money, because a year of full access to all the apps and website costs $100 (though a year of access to the app alone is only $10).

Lumosity

Lumosity and Lumosity Mobile are iPad and iPhone versions of the same app; you can also play Luminosity's games on the company's website, like Fit Brains. Lumosity's games are easy to understand and fun, but they seem limited. Unlike Elevate or Fit Brains, you can't see all the available games and choose a specific function to train.

Lumosity uses a Lumosity Performance Index to track your progress, but with the free version of the game you can't compare your brain with others. (It's $60 a year to have full access.) However, only 12 games are available on mobile devices; another 40 are web-only, so if you want to play this kind of game on your iPhone or iPad, this may not be the best choice.

The New York Times Crossword

One thing I found when playing these brain-training games is that they're all a bit twitchy; they all have timers, and you have to react quickly. You might as well just play Guitar Hero if you're looking to improve reactivity.

Me, I like to take my time and think when I'm exercising my brain. My game of choice is the New York Times crossword puzzle. For $40 a year, you get access to daily puzzles and a full archive, and the app is compatible with both iPad and iPhone (though it's pretty cramped on the smaller displays).

If you're not familiar with the New York Times crossword, it increases in difficulty from Monday through Saturday, and offers a larger, Thursday-level puzzle on Sundays. I can generally finish Monday to Wednesday puzzles, and if I have the time, I can solve most Sundays. But when I need a fix, I can go back through the archive (more than ten years of puzzles!) and choose another puzzle at the level I want. Crossword puzzles only help you keep the language part of your brain spry, but that kind of thinking is certainly helpful.

Peak

Peak Brain Training is an iPhone only app, with a limited free version and a $35 annual subscription after that. In my trial, the games were a lot more difficult than the other apps. There's a sliding block puzzle, where you have to connect a line (something I've never been good at), a Boggle-type word-find puzzle, and a variety of word and math puzzles. I found Peak's games to be the least interesting to play, and the app gives you no information other than the points you've scored.

All these apps may just be ways to separate you from your money, but if you find them enjoyable, why not play? Having fun is probably a good way to keep your brain active, so try some of them out and see if you want to play them regularly. One word of advice: try them out, and, if you plan to subscribe, go for a one-month subscription, rather than a year, to see if you get bored.