Intensification and habituation of experimental motion sickness in squirrel monkeys by repeated horizontal rotation

The aim of this research was to quantify the development of habituation or intensification of experimental motion sickness induced in Bolivian squirrel monkeys by repeated exposures to horizontal rotation. Incidence, frequency, and latency of vomiting responses were recorded from monkeys rotated daily in a transparent testing chamber at 30 rpm for periods of 1 or 2 hours. Data showed that more than half of the subjects revealed habituation in terms of increased latencies for vomiting. Some showed a tendency to vomit increasingly earlier with multiple daily exposures to rotation. The development of habituation and intensification was evident as early as the second day of rotation. The number of emetic episodes per day decreased as a consequence of repeated rotation, but intensification of vomiting frequency did not occur beyond the fifth day.