Figure 3.

Experience-dependent emergence of a switching mechanism that allows rapid changes of saccade latency in response to the change in reward location: before (A–C) and after (D–F) sufficient experience of the 1DR task. We hypothesize the presence of “reward-category neurons” (RWD), a key driver of the switching, that have excitatory connections to FEF neurons and direct pathway MSNs in the CD in the same hemisphere. They would become active before target onset selectively when a reward is expected on the contralateral side (see Figure 4), an assumption based on experimental observations of neuronal activity in the FEF, CD, SNr, and SC. Before sufficient experience of the 1DR task (A–C), the saccade latency changes gradually in both the small-to-big-reward transition [red in (B,C)] and the big-to-small-reward transition [blue in (B,C)] similarly by experimental observation (B) and computer simulation (C). The saccade latency data in (B) is from monkeys C, D, and T. After sufficient experience of the 1DR task (D–F), the saccade latency changes quickly as shown in experiments (E) and computer simulation (F). This is mainly due to the additional excitatory input from the reward-category neurons. Note, however, that the decrease in saccade latency in the small-to-big-reward transition [red in (E,F)] is quicker than the increase in saccade latency in the big-to-small-reward transition [blue in (E,F)]. This asymmetry is due to the asymmetric learning algorithm operated by two parallel circuits in the basal ganglia illustrated in Figure 2. Figure (E) from Matsumoto and Hikosaka (2007).