Figure 4. Effect of AMPH on the encoding of reward and effort by single neurons.

(A) Joint effort-reward encoding by ACC neurons in all sessions in the spatial bin immediately following departure from the starting feeder (star in inset). Each black circle shows the Pearson correlation coefficient between the amount of effort and firing rate of one neuron, plotted against the correlation value for reward volume and firing rate of the same neuron. The lines indicate the first principal component (PC) coefficient during pre-injection (blue) and post-injection (red) for all units in the dataset recorded for each dose. (B) First PC of the effort vs reward correlation distribution for cells recorded in all sessions with similar treatment. Each line represents one spatial bin from center feeder to side feeder. Blue lines indicate PCs prior to injection, and red lines indicate the PC for the same cells after the injection. Statistical difference of the coefficient distributions pre versus post injection is computed by the Kuiper two-sample test, and indicated by asterisks: * significant at p<0.05, **: p<0.01, ***: p<0.001. (C) AMPH-evoked changes in mean explained variance by the first PC of effort-reward distributions, showing that the relationship between reward and effort for individual cells breaks down under higher AMPH doses. (D) Post-injection change of the proportion of effort-selective cells, indicating that effort signaling is not reduced by AMPH. (E) Post-injection change in the proportion of reward-selective cells, showing that AMPH decreases reward encoding as measured by the number of cells discriminating reward volume. (F) Post-injection change in the absolute mean difference of firing rate of effort discriminating cells among trials of large vs small reward. The signaling of reward volume is decreased under 1.0 and 1.5 mg/kg. (G) AMPH-related change in the variance of neural firing around the mean firing rate in large and small reward (i.e. class-conditioned variance). The variance is not statistically different under AMPH, but tends to decrease under 1.0 mg/kg and increase under 1.5 mg/kg. Data show mean and SEM. Asterisks (*) indicate statistically significant differences at p<0.05; only comparisons with vehicle are illustrated.

Figure 4—figure supplement 1. Effort-reward tuning in key task epochs.

Polar histograms of the number of cells in each region of the space defined by the correlation of firing with effort (vertical axis) and correlation of firing with reward (horizontal axis). Prior to injection (blue lines), the population is primarily oriented along the diagonal axis bisecting quadrants Q_II and Q_IV (see inset), which signal positive and negative utility, respectively. This tuning is weakest at the barrier, but evident at both feeders as well as the approach and turn at the t-intersection. AMPH diminishes this tuning, as evident by the more uniform distribution of points after drug (red lines).