The effect of antimotion sickness drugs on habituation to motion.

The effect of antimotion sickness drugs on habituation was studied. Subjects were rotated once a day for 5 d to the malaise III end-point after receiving placebo, 1 mg scopolamine, 10 mg d-amphetamine, or the combination of 0.6 mg scopolamine with 5 mg of d-amphetamine. The placebo scores had a Spearman coefficient of correlation of 0.88 with the initial untreated tests. This demonstrated a high reliability for the M-III end-point and that little habituation resulted from the test design. The combination of 0.6 scopolamine with 5 mg amphetamine produced the fastest rate of habituation closely followed by the dose of 1 mg scopolamine. 10 mg of d-amphetamine also produced an increase in habituation over placebo scores. When the medications were discontinued on day 5 a rebound in sensitivity to vestibular stimulation occurred with scopolamine and scopolamine with d-amphetamine. The increased habituation appears to be due to the greater exposure to vestibular stimulation permitted by the medications.

Differential effects of scopolamine and amphetamine on microcomputer-based performance tests.

Scopolamine (1.0 mg) and d-amphetamine (10 mg) were administered alone and in combination to 16 subjects (medical students), randomly assigned to testing sessions in a fully crossed-over (Latin square) within-subjects design. After being practiced to stability, 9 performance tests from a menu of portable microcomputer-based tests were administered double-blind over 4 weekly treatments (including a placebo). Differential effects of drugs on performance were found. Motor and perceptual speed tests appeared enhanced by d-amphetamine and not degraded by scopolamine. Two of the five cognitive tests showed reductions with scopolamine. The findings are discussed in connection with using a menu of performance tests that can have diagnostic significance for assessment of drug treatments. The effects of scopolamine in this study and others are considered in terms of a model which implies that magnitude of performance deficit depends on performance type (cognitive, motor, self-report) and dosage level. Applying the model, we offer the following summary: below 0.15 mg scopolamine is without any effect; below 0.50 mg, the effect is limited, but can be revealed by some sensitive, complex performance tests and self-report; above 1.0 mg, the effect is likely to impact on operational efficiency.