Since the start of the wars in Iraq and Afghanistan, there has been a large and steady rise in the prevalence of post-traumatic stress disorder among our troops. One recent study of ... Americans who served in those countries found that the rates of the disorder jumped to 22 percent in 2008 from just 0.2 percent in 2002. [A] factor that might be playing a role in the increasing rates of the disorder ... has escaped attention: the military's use of stimulant medications, like Ritalin and Adderall, in our troops. Annual spending on stimulants jumped to $39 million in 2010 from $7.5 million in 2001 - more than a fivefold increase. The number of Ritalin and Adderall prescriptions written for active-duty service members increased by nearly 1,000 percent in five years, to 32,000 from 3,000. The military almost certainly uses the stimulants to help fatigued and sleep-deprived troops stay alert. By causing the direct release of norepinephrine - a close chemical relative of adrenaline - in the brain, stimulants facilitate memory formation. Not surprisingly, emotionally arousing experiences - both positive and negative - also cause a surge of norepinephrine, which helps to create vivid, long-lasting memories. That's why we tend to remember events that stir our feelings and learn best when we are a little anxious. Since PTSD is basically a pathological form of learning known as fear conditioning, stimulants could plausibly increase the risk of getting the disorder. It is an open question whether the use of stimulants in combat does more good than harm.