Figure 1

Recognition of a 3D object from a 2D picture is hippocampal dependent regardless of symmetry. (a) Representative infusion sites within the CA1 region of dorsal hippocampus and representative photomicrograph of cannula placement (inset). (b) Each mouse explored two identical novel pictures of a radially symmetric metal leveling foot during sample session (top left). Upon acquiring sample session picture exploration criterion, the mouse was removed and received bilateral intrahippocampal saline or muscimol. During the test session 24 h later (top right), a novel picture replaced one of the familiar pictures. Saline-treated mice explored the novel picture significantly more than the familiar picture during the test session, behavior consistent with visual recognition memory. However, post-sample muscimol-treated mice explored both pictures equivalently, indicating a failure of recognition memory. Discrimination ratio scores were significantly different between the post-sample treatment groups; this difference between the groups was not due to a difference in overall object exploration during the test session. *P < 0.01 versus the respective saline condition. (c) The sample session was conducted as in Fig. 1b. During the test session 24 h later (top right), the 2D familiar pictures were replaced with a 3D “familiar” object (i.e., viewed previously in picture form) and a 3D novel object. Saline-treated mice explored the novel object significantly more than the "familiar" during the 5-min test session; behavior consistent with picture-object correspondence. Muscimol-treated mice explored both objects equivalently, implying that hippocampal inactivation impaired memory for the pictured object, and consequently these mice failed to exhibit test session behavior consistent with picture-object correspondence. A second cohort of saline- and muscimol-treated mice explored the novel object more than the familiar when given a 10-min test session. *P < 0.05 versus respective saline condition. (d) From within a Plexiglas insert, the sample session was conducted as in Fig. 1b&c; however, the stimuli were pictures of a radially asymmetric monkey. The 5-min test session was conducted as in Fig. 1c. Saline-treated mice explored the novel object significantly more than the "familiar" during the test session; behavior consistent with picture-object correspondence. Muscimol-treated mice explored both objects equivalently, implying that hippocampal inactivation impaired memory for the pictured object, and consequently these mice failed to exhibit test session behavior consistent with picture-object correspondence.