Figure 1.

Task design. A, Experimental apparatus. B, Sequence of events in a trial of the amount gambling task (top) and delay gambling task (bottom). The rats were required to nose-poke to initiate a trial, and then to press a lever. Water was given as reward. Both tasks required the rats to choose between a risky option and a sure option. C, Session structure. In the first 40 forced trials, the rats learned the relationship between the lever positions and the outcomes. In the following 100 free choice trials, the rats were free to choose between the two options.