Furthermore,

reduced behavioral responding to A1 was inversely correlated with neural summation measured earlier, in the first compound training session (Figure 4G, right). In other words, the stronger the signaling of novel summed expectancies for reward during compound training in a given rat, the weaker responding to the A1 cue was at the start of extinction training. Thus, Anticancer Compound Library neural estimates of outcomes in OFC were predictive of both behavior and learning. The neural data described above suggests that elevated activity in OFC to the compound cue is critical for learning. This is consistent with earlier data in which we showed that pharmacological inactivation of OFC during compound training prevented learning, assessed later during the probe test. However as noted earlier, this work is also consistent with other explanations, since activity within

OFC is suppressed throughout compound training in a nonspecific manner. To provide a more specific causal test of this hypothesis, we next used optogenetic methods to inhibit activity of OFC neurons just at the time of presentation of the compound cue. Rats received bilateral infusions of either AAV-CaMKIIa-eNpHR3.0-eYFP (halo, n = 11 C59 wnt cell line including nine that underwent behavioral testing and two additional rats used for ex vivo recording) or AAV-CaMKIIa-eYFP (control, n = 9) into OFC at the same location as our recording work; expression was verified histologically postmortem (Figures 5A–5C). Light-dependent inhibition of OFC neurons was tested using ex vivo recording in two rats

(Figure 5D). The remaining rats (n values = 9) received fiber optic assemblies immediately over the injection sites. Three weeks after surgery, these rats began training in else the same overexpectation task described above, except that light was delivered into the OFC bilaterally during the presentation of the compound cue (Figure 5E). While there were neither main effects nor any interactions of group on conditioned responding across either conditioning (F values < 0.91; p values > 0.61) or during the compound sessions (F values < 2.41; p values > 0.08; Figure S5 available online), there were significant differences during the subsequent probe test. Specifically, NpHR rats in whom light was delivered during the compound cue failed to show any difference in conditioned responding to the A1 versus A2 cues in the subsequent probe test (Figure 5F), whereas eYFP rats that received the same treatment responded much less to A1 than to A2 (Figure 5G), particularly on the very first trial of the extinction probe test. This impression was confirmed by a two-factor ANOVA (cue X group) comparing responding to A1 versus A2 on the first trial, which revealed a significant main effect of group (F(1,16) = 9.68; p < 0.