Partial Reinforcement Reduces Vulnerability to Anti-anxiety Self-medication During Appetitive Extinction

Inbred rats from the Roman low-avoidance strain (RLA-I), but not from the Roman high-avoidance strain (RHA-I) increased preference for ethanol after being exposed to sessions of appetitive extinction (Manzo et al. Physiol Behav 2014 123:86-92). RLA-I rats have shown greater sensitivity than RHA-I rats to a variety of anxiogenic situations, including those involving reward loss. Such increased fluid preference did not occur after acquisition (reinforced) sessions or in control groups with postsession access to water, rather than ethanol. Because ethanol has anxiolytic properties in tasks involving reward loss, oral consumption after extinction sessions was interpreted as anti-anxiety or emotional self-medication (ESM). The present research was an attempt to reduce or eliminate the ESM effect in RLA-I rats by giving them 50% partial reinforcement training during the acquisition of an instrumental response, a treatment known to induce resilience to loss-induced anxiety. As expected, partially reinforced RLA-I rats showed a higher resistance to extinction in comparison to continuously reinforced animals, displaying lower ethanol consumption than continuously reinforced rats during the postsession preference test. Partial and continuous control groups receiving water during the preference tests showed no changes in preference. These results suggest that exposure to reward uncertainty typical of partial reinforcement training can reduce ESM in rats genetically selected for high levels of anxiety.

Partial Delay and Partial Reinforcement Effects on Resistance to Continuous Delay: Some Effects of Sequential Manipulations

Rats were trained in a straight-alley runway in two replications of 24 rats each. Two groups received partial reinforcement training with one or three successive nonreward trials (N-length), two groups received partial delay training with one and three successive delayed trials (D-length), and two additional groups received immediate continuous reinforcement. Following training all groups were shifted to continuous delay. The results indicated that D-length increased resistance to continuous delay, however, N-length did not have the corresponding effect. The performance of both N-length groups equalled that of the D-length 3 group, but the D-length 1 group was inferior and not different from the continuously reinforced control groups. These results were discussed in terms of Capaldi's (1967) sequential theory of instrumental learning.

Partial Reinforcement of Social Behavior in Rats

The effects of partial reinforcement on a social response were studied in 2 groups of rats. One group was trained to follow other rats on a continuous schedule and the other on a partial (50%) schedule. Animals having partial reinforcement training performed at a higher level during extinction than those trained under continuous reinforcement. The results were interpreted as extending reinforcement schedule effects to animal social behavior.