Each monkey sat in a testing room, unrestrained, in a wheeled transport cage placed 20 cm from a touch-sensitive monitor (38 cm wide × 28 cm high) on which pairs of visual stimuli could be presented (eight-bit colour clipart bitmap images, 128 × 128 pixels) and responses recorded. Rewards (190-mg Noyes pellets) were delivered from a dispenser (MED Associates, St Albans, Vermont) into a food well immediately to the right of the touch screen. A large metal food box, situated to the left below the touch screen, contained each individual’s daily food allowance

(given in addition to the reward pellets) consisting of proprietary monkey food, fruit, peanuts and seeds, delivered immediately after testing each day. This was supplemented by a forage mix of seeds and grains given ∼6 h prior to testing in the home cage. Stimulus presentation, experimental contingencies, reward Epacadostat ic50 selleckchem delivery and food box opening was controlled by a computer using in-house software. The mOFC animals were tested pre- and postoperatively on

a simple two-choice task. Before the start of testing, all macaques had received extensive training with touch screens and knew that touching a stimulus on the screen could lead to food reward. Each day, macaques were presented with two novel stimuli on the touch screen at the same time in a left/right configuration. Each stimulus’ side of presentation varied from trial to trial. On each trial, selecting one stimulus caused the other to extinguish and reward to be delivered according to the reward schedule. Auditory tones were used to cue the animal to the presentation of the stimuli, to the selection of a stimulus and to the potential delivery of a reward. Each stimulus was associated with a different Pregnenolone outcome probability,

one stimulus always being rewarded more than the other. At the start of testing, each stimulus was randomly assigned one of two reward probabilities (Fig. 6A). The ratios of reward associated with the two stimuli were either 75 : 25 (in other words one stimulus had a 0.75 probability of reward while the other had a 0.25 probability of reward) or 50 : 18. Each schedule was performed twice and in an interleaved manner. Monkeys’ touches registered their stimulus selections. Upon a decision being made rewards were delivered according to a specific schedule (75 : 25 and 50 : 18) with a fixed probability with a reward matching contingency in place (Herrnstein, 1997; Sugrue et al., 2004; Kennerley et al., 2006; Rudebeck et al., 2008b). This meant that rewards once allocated to a stimulus remained available until that stimulus was chosen. Further details can be found in Rudebeck et al. (2008b).