Figure 1
Delay discounting task and location of micro-injections. (A) Timeline of the instrumental paradigm in which each animal was required to make choices between a small immediate reward and a larger delayed one. A trial began when a small white dot appeared at the center of the screen and the monkey held the resting key with its left hand. Then, two peripheral cues were presented on the monitor. One of them was a conditioned stimulus associated with a small immediate reward, whereas the other cue indicated a larger delayed reward. Six different visual cues per animal were used for different delays set between 0 and 12 seconds. After offset of the peripheral cues, two green squares were displayed (the go signal), thereby cueing the animal to release the resting key and to select one of the targets. Depending on the chosen target, fruit juice was then delivered after the selected reward delay period (small immediate reward vs. large delayed one). Independent of animal choices (immediate or delayed reward after the target touching), all trials were followed by a 0.8-s inter-trial interval (ITI). (B) Schematic map of intra-striatal microinjection sites in the right caudate nucleus (CdN), and the right ventral striatum (VS). The sites were fairly close between the animals.
