Diazepam and decision making in the rat: negative evidence for reduced tolerance to reward delay.

A laboratory decision-making paradigm was developed in which changes in behavioural planning in response to delays in reward delivery could be studied in the rat. The problem given was to choose between three behavioural options, lever-pressing or running into one of two arms fitted to the experimental chamber, in order to obtain rewards (water). Basically, the animal received rewards with a certain probability when pressing the lever. At certain random intervals, reward delivery by lever-presses was stopped. To restart the system, the animal had to abandon lever-pressing and run out into one of the arms. The arm lengths could be varied, and a time-delay for restarting the system could be introduced into one of the arms. These manipulations changed the arm preference so that a long arm, or an arm with a time delay, was avoided. It was specifically investigated whether the benzodiazepine diazepam selectively lowered the tolerance to accept reward delay. Such an effect of benzodiazepines has previously been proposed. After diazepam 1 mg/kg, the number of lever-presses before running into an arm and number of behavioural interruptions were increased, and interpreted to show a deficit in information processing and/or decision making. No evidence for a selective effect of diazepam to reduce tolerance to reward delays could be detected.