Twenty-four healthy men between the ages of 21 and 35 participated in this placebo-controlled, double-blind, crossover study. An oral dose of 30 mg PB or a placebo was administered three times daily for 5 days with crossover after a 1-week period of “washout.” Testing of study variables was performed on days 2, 4, and 5 of treatment and 3 days after cessation of each treatment.

On day 2 of PB intake, performance was worse on a visual probability monitoring task (a test of perception and reaction time). On days 4 and 5, PB treatment was associated with decrements in dual-task performance. For example, when a visual tracking task was performed simultaneously with a memory search task, there was a tendency for the memory task to be more disrupted under PB treatment than under placebo conditions. Interestingly, PB significantly improved tests of hand steadiness on days 4 and 5. No adverse health effects were observed, and measures of subjective state and daily work activities failed to distinguish a difference between PB and placebo treatment. The authors concluded that PB, in the doses used, is well tolerated by healthy young men. However, the subtle decrements in cognitive function were considered noteworthy since they related to complex functions, which might be of particular importance in military operations. The rapid and precise actions required of an F-16 pilot were cited as an example of such performance demands (Graham and Cook, 1984).

Thomas and colleagues (1990) studied the effects of PB on cognitive performance of ten U.S. Navy divers during extended heat and warm water exposures. After prolonged pre-dive heat exposure, followed by a 3-hour dive, tests of short-term memory, learning acquisition, vision, and coordination were administered. For 2 days prior to and during one of the test exposures, subjects were treated with oral PB. Before and during another exposure, placebo was orally administered. The dose of PB is not stated. Short-term memory and measures of learning were impaired after heat exposure dives. No differences between PB and placebo-treated subjects were observed for any of the study parameters. The authors interpreted the findings as revealing that heat stress has a clear effect on the performance of complex cognitive tasks, but that PB had no such effect on behavioral or psychophysiological performance when administered either alone or in combination with heat stress (Thomas et al., 1990).

In summary, the 1984 study by Graham and Cook (1984) of the effects of PB on multiple parameters of performance provides a remarkably comprehensive and subtle assessment of psychomotor and cognitive functions in volunteers treated with doses of PB likely to have been used in the Gulf War. Although tests of many psychomotor and cognitive functions are unaffected by PB, there appears to be a trend for decrements in performance of complex tasks involving rapid shifts of attention. The study suggests subtle effects of this drug on cognition, reaction time, and complex performance that are not, however, supported by the prevailing concepts regarding the inability of PB to penetrate the blood– brain barrier. Although there was no evidence of persistent effects 3 days after discontinuation of the drug, suggesting that these are short-term effects, no long-term follow-up was reported.

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