Figure 1.

a, Conditional discrimination task. The two contexts (represented by different shadings) differed in their flooring (wood vs black paper for the initial conditional discrimination and rubber vs sandpaper for the second discrimination problem) and in the walls (white vs black paper for the initial conditional discrimination and vertical vs horizontal stripes for the second). The stimulus objects (X or Y) differed in odor and in the medium that filled the pots (shown as blue and yellow). b, Lesion marks made at tips of tetrodes, one located in CA1 and two others in the CA3 region of hippocampus.