Figure 1. Microstructural organization of instrumental behavior.

(A) Hungry rats were trained to perform a self-paced ‘reward seeking’ task, in which pressing a lever was intermittently reinforced with food pellets (RI-60s schedule). Press-contingent food-cup approaches were taken as a measure of attempted ‘reward retrieval’. (B) Probability of food-cup approaches as a function of time surrounding reinforced (purple) and nonreinforced (gray) lever presses. (C) Representative pattern of food-cup approach behavior for an individual rat surrounding reinforced and nonreinforced lever presses. Individual reinforced trials are separately presented across the y-axis aligned at the point at which the lever became activated (i.e., primed for reinforcement). (D, E) Effects of manipulating instrumental reinforcement contingency on the organization of reward-seeking and -retrieval responses. Total lever presses (D) or presses followed by an approach (E) during tests in which lever pressing was intermittently reinforced (RI-60s) either with food pellets and associated cues (Food and Cues) or with pellet dispenser cues but no actual food delivery (Cues Only). Rats were also tested without any reinforcement (No Food or Cues). (F) The proportion of lever presses that were followed by food-cup approach was higher for reinforced presses than for nonreinforced presses, regardless of whether pressing was reinforced with Food and Cues, or Cues Only. Rats also continued to sporadically check the food cup after nonreinforced lever presses, albeit at a much lower level than after reinforced presses.