Note: I wrote this as a response to a comment on one of my articles about how brain games don’t have enough evidence to really back up their claims that they improve general cognition, and it ended up getting weighty enough that I thought it merited its own (slightly edited) blog post.
Most of the confirmed effects of video games on cognition that I know of are near-transfer, mostly on a physically measurable scale. Strengthening hand-eye-coordination is a little more concrete and closer to being near transfer than far transfer, since the skill you’re training by reacting to an enemy on screen (quick response to visual stimuli) is very similar to skills you would need in other quick-response settings.
The problem with cognitive effects of games and other mental activities is that not only are they harder to measure by default, but they’re almost all examples of far transfer, or skill transfer between dissimilar domains. The existence of near transfer tasks, like playing video games and getting better at other video games, seems pretty intuitive, but extending that intuition to far transfer gets pretty hazy. It’s totally possible that playing chess does strengthen a certain part of our brain and leads to something neurologically measurable, but whether that then translates to improved performance at something like math or stock trading is difficult to figure out at best, and most studies so far haven’t found much evidence for it.
For example, here’s a recent meta-analysis on chess and music: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5724589/
So it’s really not just brain training games where the skills are non-transferable, it’s pretty much any cognitive activity. Playing one instrument will probably help you play other instruments better, but maybe it won’t be as helpful for learning Chinese. The issue with brain-training games isn’t that they’re useless, it’s more that they rely on the idea that far transfer works, and the only skill they really build is peoples’ ability to get good at their games. If the skill you want to train is puzzle-solving, you’re good to go; it’ll give you puzzle training + a few other cognitive perk-ups.
General brain activity is pretty scientifically proven to be a good thing (lots of studies have found correlations between high levels of brain activity leading to lower levels of dementia, for example), so brain training games are probably a fine way to keep your brain ticking. If you’re doing brain training hoping it’ll boost your general intelligence and help you pass an exam or something in the future, though, you’re better off just studying that thing. As far as we know, one type of cognitive activity is as good as another, so you might as well just directly target the skill you want.
Actual exercise might actually be a better option for improving overall brain function and memory, though! There’s a big literature coming out these days on how especially cardiovascular activity is strongly linked to better cognition, which points again to a lot of these more general factors being mostly physical, and perhaps marginally affected by cognitive input.