Just wanted to stop in quickly to share this:
http://happyherbivore.com/2012/06/herbie-week-jessica/
Although it's not directly related to post-concussion syndrome, it does echo the experience I had this spring after I switched to a vegan (plant-based) diet as part of the Nedley program. My headaches and cognitive impairments became much less pronounced, and my muscle/nerve pain disappeared almost completely.
I do still have some troubles, but they are MUCH MUCH less severe than they were.