motioninduced sickness following bilateral ablation of area postrema in squirrel monkeys using squirrel monkeys as experimental subjects we reexamined the disputed role of the area postrema ap in motioninduced vomiting after anesthetization the obex and rhomboid fossa were exposed surgically and the ap was ablated by thermal coagulation using either a battery cautery or a co2 microsurgical laser sham operations were performed on another sample of monkeys two or more weeks after surgery all animals were given 10 daily 2hour horizontal rotations at 30 rpm every monkey in both the lesions and sham samples vomited on two or more test days while the vomiting characteristics were modified following ablation of ap its function is not indispensible for the development of motion sickness in horizontallyrotated squirrel monkeys