Several illnesses expressed somatically that do not have clearly demonstrated pathophysiological origin and that are associated with neuropsychological complaints are reviewed. Among them are nonepileptic seizures, fibromyalgia, chronic fatigue syndrome, Persian Gulf War unexplained illnesses, toxic mold and sick building syndrome, and silicone breast implant disease. Some of these illnesses may be associated with objective cognitive abnormalities, but it is not likely that these abnormalities are caused by traditionally defined neurological disease. Instead, the cognitive abnormalities may be caused by a complex interaction between biological and psychological factors. Nonepileptic seizures serve as an excellent model of medically unexplained symptoms. Although nonepileptic seizures clearly are associated with objective cognitive abnormalities, they are not of neurological origin. There is evidence that severe stressors and PTSD are associated with immune system problems, neurochemical changes, and various diseases; these data blur the distinctions between psychological and organic etiologies. Diagnostic problems are intensified by the fact that many patients are poor historians. Patients are prone to omit history of severe stressors and psychiatric problems, and the inability to talk about stressors increases the likelihood of suffering from physiological forms of stress.

A series of 12 psychological and 7 neurobehavioral performance tests were administered twice to a nonclinical normative sample with 1 week between administrations. The tests were presented in a self-administered computerized format. One week test-retest reliabilities were comparable to conventional administration formats. The results suggest that individual test reliability is not affected when tests are administered as part of an extensive multi-measure battery. Computer administered test reliability coefficients also were compared to a Mixed Format (computer-conventional) administration with mixed format reliabilities generally similar to the reliabilities of published conventional tests but also generally lower than same format testing. Compared to psychological test reliability, neurobehavioral test reliability appeared more vulnerable to decreases with mixed format testing. These conclusions should not be generalized to all computer implemented tests as the qualities of the test implementation will affect the outcome.

Reports of low-concentration nerve gas exposures during the Persian Gulf War have spurred concern about possible health consequences and refocused interest on the symptoms reported by many returning military veterans. The Portland Environmental Hazards Research Center is studying veterans from the Northwest USA who report persistent, unexplained " Persian Gulf" symptoms (cases) or who do not report those symptoms (controls). Of the first 101 veterans studied, cases differed substantially from controls on a broad range of psychological tests indicative of increased distress. A subgroup of cases was identified with objective deficits on neurobehavioral tests of memory, attention, and response speed. (JINS, 1999, 5, 203-212.)

Our results revealed that Gulf War veterans who report symptoms associated with that conflict differed on multiple psychological measures in the direction of increased distress and performed more poorly on neurobehavioral measures when compared with control subjects who did not report symptoms. This suggests that psychological differences have a prominent role in investigation of possible explanations of Gulf War symptoms.