Figure 1.

a, Coronal sections showing the locations of chronically implanted electrodes. Brain atlas sections are from Paxinos and Watson (2005). b, The trial structure was the same in both deterministic and probabilistic tasks. A session contained 160 trials in 20 blocks, with four forced-choice (two on each lever) followed by four free-choice trials. In the probabilistic task, lever presses on the 75% lever resulted in four 20 mg food pellets on 75% of trials and one pellet on 25% of trials. Probabilities were reversed for the 25% lever. In the deterministic task, the two levers guaranteed four pellets or one pellet, respectively.