Figure 3. Changes in reward-evoked activity of reward-responsive dopamine neurons (n = 60) to changes in reward number.

(A – B) Average firing on first 5 (red) and last 5 (blue) trials after a shift in reward number. (A) shows firing to the 3 drops of the big reward when the small reward had been expected, and (B) shows firing to the single drop of the small reward when the big reward had been expected. Big-B, 3 drops of reward B; small-A, one drop of reward A. (C) Distributions of difference scores comparing firing to 1^st (left), 2^nd (middle) and 3^rd drops (right) of the big reward in the first 5 versus last 5 trials in a number shift block. (D) Distributions of difference scores comparing firing to the single drop of the small reward (left), and omissions of 2^nd (middle) and 3^rd drops (right) of the big reward in the first 5 versus last 5 trials in a number shift block. Difference scores were computed from the average firing rate of each neuron. The numbers in each panel indicate results of Wilcoxon signed-rank test (p) and the average difference score (u). (E) Changes in average firing before and after reward number shift. Light-gray, black and dark-gray solid lines indicate firing at the time of the 1^st, 2^nd, and 3^rd drop of reward on big trials. Light-gray, black and dark-gray dashed-lines indicate firing at the time of the small reward, and omissions of the 2^nd and 3^rd drops thereafter on small trials. Error bars, S.E.M. (F) Correlation between differences scores representing changes in firing to delivery and omission of the 2^nd drop of the big reward.