Figure 1.

Experimental design and histology. a, Rat performing the SOR task. X represents the familiar image, i.e., presented in the sample and choice periods. Y represents the novel image, i.e., presented only in the choice period. A 5 min delay separated the two periods. b, Three experimental paradigms. In all paradigms, two identical images (XX) were always presented in the sample period. The standard configuration was XX→XY. In some experiments, the two sample images were both presented again at choice (XX→XX). In other experiments, two novel identical images were presented at choice (XX→YY). c, Expression of ChR2-EYFP (green) in a 30-μm-thick coronal section in caudal PER in a representative subject. Neurons are labeled with DAPI (blue). Position of the fiber is indicated. Scale bars: c, d, 250 μm d, Example of excitotoxic lesion for the same subject labeled for NeuN and counterstained for Nissl bodies. e, Schematic of the location of the tapered optical fiber. f, Contours showing locations of optical fiber tips. All fiber tips were located in caudal PER. The solid dots are for Study A and the open dots are for Study B. Scale bar, 500 μm. RS, Rhinal sulcus; 36p, caudal PER area 36.