Mechanisms and performance measures in mastery-based incremental repeated acquisition: behavioral and pharmacological analyses.

RATIONALE: Low doses of D: -amphetamine may enhance learning, depending on the conditions under which learning is studied.
OBJECTIVE: The objective of this study is to evaluate the sensitivity of procedural variations of an incremental repeated acquisition procedure to very low-dose D: -amphetamine administration.
METHODS: A 60-min 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 (five rats) and forward (five 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) were imposed. Some learning chains had an embedded repeated response (e.g., LRRB), and others had no such repeat (e.g., LRLB). The product of chain length and number of reinforcers divided by total reinforcers was the primary marker of progress during a session (i.e., progress quotient (PQ)). After behavior stabilized, D: -amphetamine (0.01-3.0 mg/kg, i.p.) was administered.
RESULTS: Acquisition was 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.
CONCLUSIONS: Under some conditions, low doses of D: -amphetamine enhanced learning for one training procedure group. A novel dependent measure ("PQ") was a superior marker of progress on this mastery-based learning task.