Figure 9.

Coding of stimulus-outcome (S-O) association. (A) Proportions of neurons coding rewards (outcomes: O) (i), conditions (stimuli: S) (ii) and S-O associations (iii). Regression analysis was performed on data from trials in which rats made a choice to the optimal side of fixed-reward condition. The proportion of neurons that had significant regression coefficients is shown: p < 0.01 in a two-sided Student's t-test. Lines and symbols as in Figure 8A. (B) Representative dorsomedial striatal neuron encoding the S-O association. Neural activities at the onset of reward or no-reward cues are shown, as in the right column of (A). Green and orange colors show activities in rewarded trials in the variable- and fixed-reward conditions, respectively. Light blue and red colors show non-rewarded trials. Lines and symbols as in Figure 8B. (C) Detailed neural coding of S-O associations in the dorsomedial striatum. The proportion of neurons encoding one of the four associations is shown before and after the onset of reward or no-reward cues, as in (B). Colors correspond to (B). Many striatal neurons encoded the no-reward cue in the variable-reward condition, indicating that they did not differentiate reward and no-reward cues in the fixed-reward condition.