Parasympathetic nervous system at risk.

• Position: Gulf War Syndrome

Damage to the parasympathetic nervous system may account for nearly half of the typical symptoms-including gallbladder disease, unrefreshing sleep, depression, joint pain, chronic diarrhea, and sexual dysfunction-that afflict those with Gulf War syndrome, according to a study by the University of Texas Southwestern Medical Center at Dallas.

"The high rate of gallbladder disease in these men, reported in a previous study, is particularly disturbing because typically women over 40 get this. It's singularly rare in young men," states Robert Haley, lead author and chief of epidemiology.

The parasympathetic system regulates primitive, automatic bodily functions such as digestion and sleep, while the sympathetic nervous system controls the "fight or flight" instinct. "They're sort of the mirror image of each other--the yin and the yang of the nervous system-that control functions we are not usually aware of. This is another part of the explanation as to why Gulf War syndrome is so elusive and mysterious:'

Previously, isolating pure parasympathetic brain function was difficult. Haley and his colleagues, however, used a technique that monitors fluctuations in approximately 100,000 heartbeats over 24 hours and measures fluctuations in high-frequency heart-rate variability--a function solely regulated by the parasympathetic nervous system.

After plotting the subtle alterations in heart function using a mathematical technique called spectral analysis, researchers found that parasympathetic brain function, which usually peaks during...