Effects of Different Intensities of Electric Shock on the Production of Immunization to Learned Helplessness in Rats

Abstract

Organisms exposed to uncontrollable aversive stimuli subsequently show difficulties in operant learning, an effect known as learned helplessness. Prior exposure to controllable aversive stimuli can prevent, totally or partially, this effect (referred to as immunization). The present study aimed to investigate whether prior exposure to different intensities of electric shocks could produce varying levels of immunization. Three sessions were conducted: (1) escape contingency (snoutpoking), with shocks of 0,6 or 1,0 mA; (2) uncontrollable shocks at 1,0 mA; and (3) test session with an escape contingency (jumping), also with 1,0 mA shocks. Thirty-two rats were divided into four groups (n = 8): NN, NI, CI 1,0, and CI 0,6. Subjects in groups CI 0,6 and CI 1,0 participated in all three sessions, differing only in the shock intensity of the first session (0,6 or 1,0 mA, respectively); subjects in group NI participated in Sessions 2 and 3; and those in group NN only in Session 3. Results showed that, in Session 1, CI 1,0 subjects learned the escape response, while CI 0,6 subjects showed only incipient learning; in Session 3, only the NI group failed to acquire the escape response; CI 1,0 animals showed learning patterns similar to the NN group, and CI 0,6 animals learned more slowly but eventually reached comparable performance levels. These results replicate the effects of learned helplessness (NI group) and immunization (CI 0,6 and CI 1,0). They also suggest that shock intensity may influence learning patterns during both initial exposure and testing. Possible variables to be controlled in future studies are discussed to better understand what determines different patterns of immunization.