I confess, I never thought of searching "yoga" in PubMed (though I search "lyme" and "tick" all the time. To a certain extent, it's a similar experience: frustrating. There's plenty of "yoga helps X" out there, but it's pretty vague, not a lot of what kind, how much, how long, information. Like this one: The Acute Effects of Yoga on Executive Function. Cognitive performance improves more after a yoga session than after, say, aerobics. Does it last? Are the effects cumulative? What kind of yoga? Can't tell. But, if my brain works better after yoga, that's good information, if incomplete and unsatisfying.
This, though, is more helpful: Finger dexterity and visual discrimination following two yoga breathing practices. Two groups, one practicing kabalabhati, the other practicing "breath awareness." The first group did way better. At least one other study shows that kabalabhati breathing is good for your brain, though you've got to practice for at least 15 minutes to get the real benefits.
My brain can use all the help it can get right now, so kabalabhati is going into my practice immediately.