DG somatostatin cells regulate the encoding of spatial recognition memory. (A) Schematic representation of the spontaneous location recognition test used in three versions (large = 180°, medium = 120°, and small = 50° separation) to assess spatial memory. Note that angular distance between B and C objects change in training. (B) DI accumulated over the entire behavioral test (5 min) for animals performing the three different versions. Note that only the small separation is not discriminated. One-way ANOVA, P = 0.0057; Tukey post-hoc test; ^**P = 0.039; ^***P = 0.006. (C) Total exploration time of test objects accumulated over the entire session for every version of the test, One-way ANOVA, P = 0.26. (D) Schematic representation of the medium version of the spontaneous location recognition test combined with optogenetic stimulations (blue line; 5 s-pulse every 15 s, 15 mW) delivered during training. Bottom, coronal Nissl-stained coronal hippocampus section showing the track of the chronically implanted optic fiber (arrow). (E) DI accumulated over the entire behavioral test for animals performing the intermediate version of the spontaneous location recognition test combined with optogenetic stimulation. Unpaired Student’s t-test; ^*P = 0.03. (F) Total exploration time of test objects accumulated over the complete session. Unpaired Student’s t-test; P = 0.94.