Operant behavior of rats under fixed-interval reinforcement schedules: a dynamical analysis via the extended return...

The extended-return-map was employed to analyze the inter-response time data of operant experiments using fixed-interval schedules and food reinforcement. After intensive training over numerous sessions, rats gradually developed several types of temporal patterns of lever pressing behaviors, which were visualized through different patterns of data point distributions in the extended-return-map. Analyses with randomly shuffled data sets confirmed that these patterns depended on the sequential order of the inter-response time data, indicating that they reflected dynamics of the behavior. A procedure was developed to quantify the difference between patterns in the extended-return-maps, thus, enabling the comparison between sessions, and between animals. Simulations suggested that, in addition to the two-state break-and-burst responding, both multiple switches of behavioral states during the inter-reinforcement periods and the acceleration of lever pressing rate should be taken into consideration for the dynamics found in the data.