This AP story posted on Military Times, described thousands of soldiers at the 101st Airborne Division in Fort Campbell, KY undergoing pre-deployment cognitive testing described as "mandatory brain-function tests". I suppose the idea is that if a soldier experiences a "TBI" or traumatic brain injury post-combat his cognitive functioning may decline.

Here is the reference:
http://www.militarytimes.com/news/2007/09/ap_braintesting_070920/

Comment: The DoD has always recognized PTSD and other mental health conditions as disabilities. The problem with mental health diagnoses is they often reflect invisible injuries. It is always helpful for the service member to have objective data documenting the disability when it comes time for a medical board. For example, orthopedic surgeons might use range of motion when documenting musculoskeletal injuries. Thus cognitive testing might provide some useful data. What about service members who have false positive tests or who are found to have a deficit in cognitive functioning? How can we protect privacy and other rights of service members while optimizing unit readiness?