sumed to be sarin was later confirmed in serum samples from the victims (Polhuijs et al., 1997).

Questionnaires were distributed at 1, 3, and 6 months after the incident to 610 patients seen at St. Luke’s International Hospital. Almost 60 percent of 475 respondents (290 patients) still reported symptoms related to the exposure, such as fear of subways, sleep disturbance, flashbacks, nightmares, and mood changes—symptoms that the authors interpreted as indicative of posttraumatic stress disorder (PTSD; Ohbu et al., 1997).

Six to eight months later, 18 symptom-free survivors with previous intermediate- and high-level exposure to sarin were tested for persistent CNS effects (Murata et al., 1997; Yokoyama et al., 1998a,b,c). At the time of their past admission to the hospital, their plasma cholinesterase had been depressed by about 25 percent of normal. Murata and colleagues (1997) first reported on their responses to sensory evoked potentials, a noninvasive method of detecting functional activity elicited by stimulation of specific nerve pathways, however any functional changes by EEG do not indicate their pathological basis. The event-related potential (ERP) (P300) and the visual-evoked potential (VEP) (P100) displayed slight yet significant prolongation in sarin-exposed subjects, compared with 18 sex- and age-matched control subjects (healthy volunteers).13 There was no relationship in the sarin-exposed group between neurophysiological findings and scores for PTSD, which were significantly elevated compared to controls (Yokoyama et al., 1998c) Short-latency brain stem auditory evoked potentials and electrocardiography were not different between cases and controls. Findings were interpreted by the authors as suggestive of long-term neurotoxic effects of high-level exposure to sarin in those individuals who no longer reported symptoms.

The same sarin-exposed individuals underwent neurobehavioral testing and vestibulocerebellar testing (Yokoyama et al., 1998a,b). For neurobehavioral testing, cases and controls filled out a PTSD checklist and underwent nine tests: digit symbol (psychomotor performance); picture completion (visual perception); digit span (attention and memory); finger tapping (psychomotor performance); reaction time (psychomotor performance); continuous performance test (sustained visual attention); paired-associate learning (learning and memory); General Health Questionnaire (psychiatric symptoms); and the Profile of Mood States. The score on the digit symbol test for sarin-exposed cases was significantly lower than for controls. The scores on the General Health Questionnaire, fatigue (Profile of Mood States), and PTSD checklist were significantly higher for the sarin group. Their scores on the digit symbol test remained significantly decreased even after controlling for the effect of PTSD. It is important to control for PTSD because studies of military trainees under mock defensive chemical


In the ERP test, subjects’ EEG was measured in response to a random sequence of tones. In the visual-evoked potential, their EEG was measured after stimulation with a checkerboard pattern, which reversed at a rate of two times per second. P300 and P100 refer to the peak electrical potential recorded by the EEG.

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