most potent protective factor, however, is a neurotransmitter called neuropeptide Y (NPY), which binds to receptors on neurons in the prefrontal cortex and alters their response to noradrenaline, acting as a brake to its accelerator pedal.

The most intriguing implication of Morgan's research, however, is the suggestion that supplementing levels of DHEA or NPY could enhance soldiers' ability to think straight in the heat of battle - and perhaps also offer some protection against PTSD.

The brain needs a large amount of energy to function, and in the food and sleep-deprived SERE trainees, the glucose proved effective at boosting their mental acuity. The following morning, those given the carbohydrate drinks performed significantly better on the Stroop test (Military Medicine, vol 174, p 132).

Giving troops energy-rich drinks is one thing, but the idea of intervening with drugs to enhance military performance is more controversial, as reactions to another proposal have shown.

The beta-blocker propranolol has the potential to lessen the fearful reactions of PTSD sufferers recalling traumatic events, but the suggestion of giving it to troops as a prophylactic has alarmed some observers, who worry that taking the emotional sting out of bad memories might make troops operate without the restraint of conscience. "Do we really want guilt-free soldiers?" asks Jonathan Moreno, a bioethicist at the University of Pennsylvania in Philadelphia.