Figure 2. Orbitofrontal neurons encode preconditioned pairs in the absence of reward.

(A) AUC normalized responding of all 266 neurons recorded across the two days of preconditioning for either A-B trials (blue, left) or C-D trials (red, right), sorted by for the relative response to cue pairs (cues AB vs CD). The plots show that different neurons seem to fire to the AB pair or the CD pair. (B) Cue-evoked firing in two individual neurons shows differential firing to either the AB or CD pair. (C) Correlations between individual neural responses to paired or unpaired cues above the neuron’s average responding. Plots reveal much greater correlated firing between paired than unpaired cues during preconditioning (A-B, top left; C-D, bottom right).

Figure 2—figure supplement 1. The correlation between pairs of cues is not solely determined by temporal contiguity.

To explore how dependent the correlation observed in Figure 2 is on the temporal adjacency of the cues, we compared the first half or second half of one of the cues presented on that trial with all other bins of that trial (scatter plots), and the first or second half of one cue with the mean firing during its paired cue (bar plots). We expected that if temporal adjacency explains much of the correlation, nearby bins should express substantially higher correlations. Here we display the results of such an analysis for both cues of a pair for neurons recorded on day 1 (left panels A and C) and 2 (right panels B and D) of preconditioning. While there is a modest difference between early vs late cue correlations, there is no significant difference between the temporal distance of early/late bins of one cue and the other cue of that pair.