Individual differences in the responses of naïve rhesus monkeys to snakes.

The authors demonstrated individual differences in inhibited behavior and withdrawal responses of laboratory-born rhesus monkeys when initially exposed to a snake. Most monkeys displayed a small significant increase in their behavioral inhibition in the presence of a snake. A few monkeys had marked responses, and some actively withdrew. Although the responses of the most extreme laboratory-born monkeys were comparable to feral-born monkeys, the responses of the laboratory-born monkeys rapidly habituated. The individual differences in the responses of naïve monkeys likely reflect a continuum from orienting to wariness to fear. A neurobiological model is presented that addresses potential mechanisms underlying these individual differences, their relation to fear, and how they may predispose to phobia development.