Adaptation and habituation of motion-induced vomiting in squirrel monkeys.

Nonrestrained adult squirrel monkeys were found to be prolific vomiters when rotated in the horizontal plane for at least 1 h with visual cues available. When multiple daily spins were given, monkeys who vomited early during the first session tended to habituate during subsequent rotations. Subjects who vomited late during the first spin tended to vomit increasingly earlier for several days before the trend reverted to habituation. When a single rotation was continued for up to 8 h, emetic waves occurred with a high probability density for about 2 h, then ceased for many hours with an occasional animal exhibiting isolated emetic episodes. Adaptation effects were transient; when retested beyond a week, most subjects vomited in less time than did inexperienced monkeys on their first exposure to rotation. Attempts to confirm the findings using sinusoidal vertical acceleration were unsuccessful because of failure to induce vomiting using this type of motion.