After a delay period, the central fixation point turned off (go signal), and the monkeys had to make a saccade to the remembered target position. Within one block of 24 trials, saccades to one position were associated with a large amount of liquid reward (large-reward trials) while check details saccades to the other position were associated with a small amount of reward (small-reward trials). In the next block of 24 trials the position-reward contingency was reversed without external instructions. Animals reliably adjusted their saccade performance along with the position-reward contingency reversals: saccades to the large-reward position had higher velocities and shorter latencies and saccades

to the small-reward position had lower velocities and longer latencies (Figures 5A and 5B). This indicates that the animals’

performance was modulated by the expected reward size. While the monkey was performing the reward-biased memory-guided saccade task, we recorded from single neurons in and around the VP which was defined as the structure below the anterior commissure (AC) and above the substantia innominata (Figures 1C and 1D), following Haber et al. (1993). The structure above the AC was defined as part of the external segment of the globus pallidus (GPe). Posterior to these regions are the main bodies of the GPe and the internal segment of the globus pallidus (GPi) (see Figure 6A). This anatomical see more classification was roughly correlated with the variation of single neuronal activity physiologically and click here functionally. In particular, reward-related neurons were found predominantly in the VP, less frequently in the GPe dorsal to the AC, and rarely in the GPe-GPi

posterior to the AC. In this study, we focused on the single neuronal activity recorded in the VP. We tested 190 neurons in the VP using the reward-biased memory-guided saccade task. Among them, 118 neurons (32 in monkey P and 86 in monkey H) (62%) showed task-related modulations. In addition to the neurons formally tested, we encountered 73 neurons which were judged to be unrelated to the task and thus were not tested formally. The average spontaneous firing rate of the task-related VP neurons was 26.6 ± 14.8 spikes/s. The average spike duration of VP neurons was 0.82 ± 0.12 ms. Figure 2 shows two examples of single VP neurons recorded in the reward-biased saccades. As shown in the raster display, both VP neurons changed their activity completely depending on the expected outcome (large or small reward), for both ipsiversive and contraversive saccades. The first VP neuron increased its activity after the onset of fixation point (Figure 2A). This neuron’s activity further increased after the appearance of the target cue indicating the delivery of large reward (large-reward cue, red), but decreased after the appearance of the cue indicating small reward (small-reward cue, blue).