There was a double blind, crossover done in Sydney a couple years back that used 5g/day and the participants supposedly increased brain processing speed, mind you these were vegetarians who can have lower CP levels to begin with.
Other than that there has been more work with ALS, MD, Alzheimer's Disease, Parkinson's, Huntington's and some other neurological disorders (few on humans but more coming soon)and Creatine, but little in the way of peer reviews with respect to these diseases.