In a study by Georgetown University Medical Center published in 2013, researchers concluded that there are subsets of those that have GSW after putting 38 participants through two physical stress tests with two fMRI tests before and after each stress test. A fMRI measures, pain, memory and automatic function. Automatic function measures the autonomic nervous system which works below conscious efforts and controls things like urination, heart rate, sexual attraction, respiration rate, salivation and more.
What they found was that there are two distinct subgroups based on which of the two parts of their brains had deteriorated from Gulf War Syndrome. Of the 28, 18 showed they experienced more pain following the stress tests and the fMRI showed they had lost brain matter from GWS in the region next to the area that regulates pain. The conclusion they reached is that doctors' diagnosis of GSW is difficult because they report very different symptoms.

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