I am a big fan of mental exercises, the "how" of how people think, and have a long-running interest in the literature on brain function and peak human performance - damn you Robert Anton Wilson for helping blow up my country boy paradigm a few decades back. A lot of literature has been popping up over the last few years on trans-cranial direct stimulation as a way of addressing the symptoms of clinical depression, as well as a method to induce the "flow state" and allow for rapid learning and mastery.
Human brain function in general fascinates me (hence my attraction to socionomics) and I've worked with light and sound machines over the years to generate interesting effects but little lasting change.
Well, I just stumbled across a site that was put up a few weeks ago to take pre-orders for a kit to build your own tDCS device. Looks like some college kids having fun, like Dell in the early days. I have signed up on the pre-order list. I am working on a self-experiment test plan. While I don't expect to become Limitless, I am very interested to see if I can improve math and verbal scoring (initially based on smartphone apps) as well as improve retention on my engineering work.
I'll post my results down the road for those interested in this type of thing as I continue to look for anything to give me an edge as we teeter here on the abyss...