Hi, well this is just from personal experience so ymmv, but I've been playing the game off and on for the past two years and am convinced of positive effects.

I do know that, beforehand, I had never been able to study for protracted periods of time and enjoy the experience - for me, studying had always been a fight against intellectual and physical restlessness (=restless legs, itching, shifting about on my seat). DnB seems not only to permit me to sit down and focus for long periods, it actually makes me want to study - I feel compelled to learn and get annoyed if prevented from doing so. And when I do study, I can now put in serious hours (typically three or four chunks of 2 1/2hr blocks).

I'm sure that this sounds somewhat implausible, but there have been many occasions on which I have been overwhelmed yet again by the determined demons of dilettantism and distraction only to remember what I had let slip from my routine.

I would not be so sure of positive effects if, after having trained for a few days, I had suffered an exacerbation of symptoms, but this has not occurred.

The simplest explanation that I can think of is that it is the only activity that forces me to use the entirety of my attention, encouraging me to eliminate distracting thoughts (as in meditation?) whilst also providing a tightly-defined focal point (the stimuli in space and time) and overarching purpose (to find order (as organizing my impressions helps me remember)). Perhaps this is where my feelings of increased purposefulness come from: the game trains me generally to enjoy drawing connections, and I begin to want to organize the world around me.