Reactions by differentially raised rhesus monkeys to noxious stimulation

Adult monkeys reared in social‐sensory isolation were compared with socially raised controls in 2 studies assessing aversive reactions to electric shock. In Experiment 1, the procedure involved competition between self‐paced thirst and shock avoidance, presenting the monkey with a situation in which it had to absorb 2‐sec of mouth‐shock on a drinking tube to obtain water. When the monkey went through a response cycle by overcoming a given shock level, taking a variable number of unshocked drinks, and going 3 min without touching the drinking tube, the current was increased one step in a range from 0.1–2.5 mA. On measures of fluid intake and time per response cycle isolate monkeys did not differ from controls, suggesting that thirst motivation did not differ between groups. On shock trials isolates tolerated higher levels of shock than controls, even though they were initially more reactive to very low current levels. Isolates also showed more negative generalized effects of shock on nonshocked drinking tube contacts at a time when controls showed almost no generalized effects. In Experiment 2, neither isolates nor controls preferred to drink from a shocked over a nonshocked tube in a 2‐choice free drinking situation, indicating that shock was a noxious stimulus for both groups. Thus, as in rats and dogs, stimulus deprivation during rearing produced anomalous reactions to noxious stimulation in monkeys.