Myths about the brain no. 7: You can train your brain via games to increase overall intelligence

This is another huge money-making industry based on dubious science. You will probably have seen them advertised ("Luminosity" on various YouTube videos is the one that springs to mind for me) or have at least heard about them. They are generally based on the principle that improving your ability to complete various tasks (usually basic maths problems or spatial navigation tasks) will result in you becoming more intelligent, improving your thinking speed or reasoning ability or any other suitably vague statement. Many of these companies claim to improve working memory, which is a cognitive system that relates to a persons ability to reason with new information and direct your attention towards the goal-relevant information contained in it (Shipstead et al., 2012). It's also been defined as your mental area where you concurrently sort and process information. Working memory has been the focus of many of these companies because of the central role working memory plays in general cognition.

So these companies advertise themselves as being able to help improve your intelligence by improving working memory (via specific tasks, usually a dual n-back test, which is simply where the user has to monitor two streams of info, one visual and one auditory and each time one or both of the streams emits a pre-established target e.g. a bird, then you have to press a button). Now there's no doubt that practicing a task will result in you getting better at it. However, the idea that practicing specific tasks will result in an improvement in a host of other mental faculties has not been shown (as detailed here, here, here and here). There has also been a study detailing why transference doesn't occur. There's also the problem that the study all this research has been based on has some serious methodological flaws in e.g. participants received training on a regular basis (whereas the controls simply went home and did whatever) so the experimental group may have had higher motivation to do well in the study, you can't measure fluid intelligence with one test. Also, when researchers tried to recreate the effect they found no significant effect as a result of training (Redick et al., 2012 and Chooi et al., 2012) which is not good news for the validity of the original study. And to cap it off, a large scale meta-analysis of studies that examined whether training working memory could result in transference of skills found no effect (Melby-Lervag et al., 2013)

So whilst it's nice to think you can increase your intelligence by performing a few tasks for a couple of weeks, it seems very unlikely that this is the case. 

References:
Berkman, E.T.; Kahn, L.E.; & Merchant, J.S. (2014). Training-Induced Changes in Inhibitory Control Network Activity. The Journal of Neuroscience, 34 (1), 149-157.
Chooi, W.T. & Thompson, L.E. (2012). Working memory training does not improve intelligence in healthy young adults. Intelligence, 40 (6), 531-542.
Jaeggi, S.M.; Buschkuehl, M.; Jonides, J.; & Perrig, W.J. (2008). Improving fluid intelligence with training on working memory. Proceedings of the National Academy of Sciences of the United States of America, 105 (19), 6829-6833.
Melby-Lervag, M. & Hulme, C. (2013). Is working memory training effective? A meta-analytic review. Developmental Psychology, 49 (2), 270-291.
Moody, D.E. (2009). Can intelligence be increased by training on a task of working memory? Intelligence, 37 (4), 327-328.
Redick, T.S.; Shipstead, Z.; Fried, D.E.; Hambrick, D.Z.; Kane, M.J.; & Engle, R.W. (2012). No Evidence of Intelligence Improvement After Working Memory Training: A Randomised, Placebo-Controlled Study. Journal of Experimental Psychology: General, 142 (2), 359-379.
Shipstead, Z.; Hicks, K.L.; & Engle, R.W. (2012). Cogmed working memory training: Does the evidence support the claims? Journal of Applied Research in Memory and Cognition, 1, 185-193.
Shipstead, Z.; Redick, T.S.; & Engle, R.W. (2010). Does Working Memory Training Generalise? Psychologica Belgica, 50 (3-4), 245-276.
Shipstead, Z.; Redick, T.S.; & Engle, R.W. (2012). Is Working Memory Training Effective? Psychological Bulletin, 138 (4), 628-654.