Effects of rearing and exposure condition upon the acquisition of phobic behaviour in cynomolgus monkeys.

Young monkeys were confronted with a harmless novel object in their familiar home-cage environment. The effects of two rearing conditions (mother and surrogate mother) and two confrontation conditions [presence and absence of the (surrogate) mother] upon the acquisition of phobic behaviour were studied. Most surrogate-reared monkeys showed persistent maladaptive avoidance behaviour with respect to the object during tests, from 7 months of age onwards. Most mother-reared monkeys approached the object during tests taking food near it, from 7 months onwards. The confrontation condition had no effect upon behaviour with respect to the object. As no aversive conditioning procedures have been applied, merely presenting a harmless object appears to be enough to set off persistent avoidance in surrogate-reared monkeys. Further investigation of the origin of the phobic behaviour is interesting in view of developing animal models of human phobias of which no conditioning history is known.