Effects of head and body restraint on experimental motion-induced sickness in squirrel monkeys

Each of 16 Bolivian-phenotype squirrel monkeys of mixed sex had a machine bolt mounted on the skull with acrylic cement; 13 were provided with temporary plaster body casts allowing free movement. With eyes open, all were rotated in the horizontal plane at 30 rpm every other day until vomiting occurred or for a maximum duration of 120 min/spin. Latencies for motion-sickness signs were recorded under three experimental conditions: free movement, torso fixed to an aluminum frame and both torso and head restrained by bolting to the frame. Subsequently, 10 monkeys from this sample were rotated while blindfolded with head and torso immobilized. Results partially confirmed human and animal findings reported by others: reduced mobility was accompanied by a reduction in the incidence and an increase in the latency of motion sickness. The importance of optokinetic input for the generation of motion sickness in this species was clear.