Figure 6.

Influence of D2 antagonist on saccadic latency. (A) Trial-by-trial changes in the latency of contralateral saccades, before (black) and after (blue) injection of a D2 antagonist into the CD. Data are from Nakamura and Hikosaka (2006). (B) Simulated trial-by-trial changes in saccade latency. (C) After D1 antagonist injection, average saccade latency increased in small-reward trials, but not in big-reward trials. The experimental data was replicated by computer simulation. (D) Hypothesized mechanism of the effect of D2 antagonist in big-reward trials. The phasic increase in the DA level exceeds both the D1 and D2 thresholds, although the D2 antagonist elevates the D2 threshold, and therefore the saccade latency remains largely unchanged. (E) Hypothesized mechanism of the effect of D2 antagonist in small-reward trials. The elevated D2 threshold eliminates the DA-dependent LTD in the indirect pathway MSNs and therefore potentiates the SNr-induced inhibition of the SC, leading to a longer latency saccade.