Figure 2.

Clustering of two groups of reward uncertainty-sensitive neurons. A, The CS epoch activity for 70 uncertainty selective neurons during the appetitive/aversive procedure. Each trace represents the average activity of a single neuron during the 6 CS epochs. We normalized each trace by dividing each of these 6 CS responses by the maximum CS response. PCA was performed on those normalized response functions. Orange and red traces represent the two clusters of neurons (Type 1 and Type 2) that resulted from the PCA analysis (shown in B, C). B, PCA performed on the single neuron functions in A revealed that the majority of the variance in the 70 neurons' CS activations can be explained by the first principal component (PC1). To assess this, we shuffled normalized activity across the 0% juice, 100% juice, 0% airpuff, 50% airpuff, and 100% airpuff CSs and calculated the percentage of variance explained (PVE) by each PC. Gray error bars represent the range of PVE for each PC based on 10,000 shuffles. C, Bimodal distribution of PC1s of the 70 uncertainty neurons (Hartigan's Dip Test, p < 0.01, tested by 10,000 permutations). Based on the PC1s, k-means clustering separated the neurons into two groups: orange represents Type 1; red represents Type 2. Their average firing is shown in D for the three CSs in each block (appetitive or aversive), separately.