Figure 3.

Population average activity of dorsal raphé neurons separated by their reward signals in response to the outcome. (A–C), Normalized activity is shown for the 1DR-MGS task, separately for positive-reward cells (A), negative-reward cells (B), and non-outcome responsive cells (C) The neurons were sorted into these categories based on significant reward discrimination during a 150–450-ms window after outcome onset (gray bar on the x-axis; p < 0.05, Wilcoxon rank-sum test). Thick lines, mean normalized activity; light shaded areas, 1 SEM. (D) Neural activity during the fixation period was positively correlated with reward coding during the target and outcome periods. The x-axis indicates the fixation period response, which was measured as the ROC area for each neuron for discriminating between its firing rate at 500–900 ms after fixation point onset vs. the pre-fixation period at 0–400 ms before fixation point onset. The y-axis indicates reward discrimination, which was the difference in reward responses between the large- and small-reward trials. The text indicates rank correlation (rho) and its p-value. The dark dots indicate neurons with a significant excitation or inhibition during the fixation period. The colored dots indicate neurons with significantly higher activity during the rewarded trials (red) or during the unrewarded trials (blue) (p < 0.05, Mann-Whitney U-test). The black lines indicate the line of best fit calculated using type 2 least-squares regression. (E,F) The first (E) and second (F) principal components of dorsal raphé neural activity profiles during the memory-guided saccade. Curves represent the normalized firing rate of the principal component during the fixation period (black) and after the onset of the rewarded (red) and unrewarded (blue) target, separately for the contralateral-rewarded block (dark colors) and ipsilateral-rewarded block (light colors). The first principal component indicated tonically increased activity during the fixation period and positive-reward coding during the target, memory, and outcome periods. The second component indicated tonically increased activity in response to reward delivery. Modified from (Bromberg-Martin et al., 2010).