Fig. 1.

Spatial delayed alternation task and performance. A: schematic of behavioral arena with sequence of primary events. In the “Choice” phase, the rat selects the right nose poke port and then traverses the chamber to collect a reward. Reward collection starts the delay period. At the end of the delay, the rat crosses back to the other side of the chamber to the alternate (left) choice port for another correct response. B: detailed sequence of events in the self-paced and controlled versions of the spatial delayed alternation (DA) task. In the self-paced version (top), after correctly responding in the choice port the rat licks the reward spout, which triggers pulsed delivery of fluid (six 0.25-s pulses of water separated by 0.50-s pauses). The rat is then free to make the next spatial choice. Choosing the opposite choice port results in another reward. In the controlled version (bottom), the rat makes a choice and then travels to the reward spout. In addition to collecting a reward during the ensuing delay, the rat must also press a lever on a variable-interval (VI) schedule (0, 5, 10, 15, or 20 s, randomly interleaved) to initiate the next choice period. Selection of the opposite choice port is rewarded. In either task variation, selection of the same choice port in consecutive trials is scored as an error and no reward is delivered. After an error, rats must initiate the next trial by contacting the reward spout (self-paced) or pressing the lever on a variable interval schedule (controlled). The trial following an error is a correction trial, in which rats must select the choice port that would have been correct. C: performance accuracy of rats in the self-paced (left, N = 3 rats that performed postoperatively) and controlled (right, N = 2 rats with isolated single units only) versions of the spatial DA task, with symbols denoting individual subjects. For the self-paced version, accuracy is presented by interresponse interval (IRI) quartile (Q1, Q2, Q3, Q4). For the controlled version, accuracy is presented by assigned delay (0, 5, 10, 15, 20 s). *P < 0.01 for shortest 3 vs. longest quartile of IRIs in the self-paced version. ^#P = 0.07 for shortest 2 vs. longest 2 assigned delays in the controlled version. D: median IRI of rats in the self-paced (left, N = 3) and controlled (right, N = 2) task variations, with symbols denoting individual subjects. The overall median of IRIs is presented for self-paced rats, while IRIs are presented by assigned delay for the controlled-delay rats. *P < 0.01 for IRIs preceding correct vs. error responses in the self-paced version. (All P values reported are from t-tests of paired samples).