Spatially Separated Response Sequences are Organized in Funtional Bouts

The rate at which an operant is produced has often functioned as a fundamental measure of the efficacy of a reinforcer. Previous research has shown that operant behavior is typically organized into bouts implying that rate of responding is a composite of bout-initiation rate, within-bout response rate, and mean bout length. However, it is still unclear whether this organization of behavioral responses into bouts is a product of the motivational processes or a property that arises from the location of an organism in space. To test this proximity hypothesis, two-response sequences were intermittently reinforced: either pressing one lever twice (manipulandum proximal to response termination) or pressing each of two levers, located on either side of an operant chamber, once (manipulandum distal to response termination). In Experiment 1, rats were first trained to lever press for food on a VI schedule before being exposed to the alternation paradigm. Experiment 1 consisted of three phases. In Phase 1, food-deprived rats learned the alternation paradigm under a tandem variable time (VT) 150-s fixed-ratio (FR) 1 schedule of reinforcement. Phase 2 and 3 increased the FR requirement from 1 to 3 or 5 and removed food deprivation, respectively, to examine their effect on response-rate components. In Experiment 2, rats switched between trials consisting of pressing a single lever repeatedly or alternating between two levers for reward. Following stable behavior, lever pressing was extinguished in both trial types to the effect of extinction on response-rate components. Overall, behavioral bouts persisted under the alternation paradigm suggesting that they reflect motivational states and not just location. Additionally, bout-initiation rate decreased with increased response effort and decreased deprivation. Taken together, these results provide support for the use of response-bout analysis to evaluate the value of a reinforcer and its sensitivity to pharmacological manipulations.