Mechanisms and Performance Measures in Mastery-Based Incremental Repeated Acquisition: Behavioral and Pharmacological Analyses

Abstract

Pharmacological and behavioral determinants of learning were examined using a mastery-based incremental repeated acquisition procedure. A 60-minute session began with a one link chain (single lever-press) that incremented to a maximum of a four-link chain using three levers: Left (L), Right (R) and Back (B). Backward (5 rats) and forward (5 rats) training procedures were used to build the chain. In pseudo-randomized presentations, a “performance” session (same chain every session) and a “learning” session (chain differed from session to session) was imposed. Some learning chains had an embedded repeated response (e.g., LRRB) and some learning chains had no such repeat (e.g., LRLB). The product of chain-length and number of reinforcers over total reinforcers quantified progress during a session (progress quotient, or “PQ”). After behavior stabilized, low doses of d-amphetamine (0.01 to 3.0 mg/kg, ip) were administered. Acquisition was consistently superior for the backward training group during non-repeating learning sessions, across all but the highest doses of d-amphetamine. Very low, clinically-relevant doses of d-amphetamine improved acquisition for the backward training group during repeating-learning sessions. This study identifies a set of conditions under which very low doses of d-amphetamine enhance learning. It also suggests a sensitive and valid measure of acquisition for use in studies of a mastery-based incremental repeated acquisition.