Fig. 1

Temporal discrimination task with in vivo calcium imaging in freely moving mice. a) Viral injection and lens implantation into dorsal hippocampus. b) Post-surgical histology of implanted mice. Expression of GCaMP6f was observed in dorsal hippocampal CA1 and CA2 (green). DAPI: blue. Lens placement was just above the hippocampus. The implant consisted of a GRIN lens (1 mm diameter) contained within a glass bottomed cannula. c) Stacked GCaMP6f image acquired through the miniature fluorescent microscope over 10 min of imaging from CA1 at 20 Hz. Specifically noted cells correspond to traces in d. d) Relative fluorescence changes (ΔF/F %) for five hippocampal CA1 cells identified in c. e) Nose poke behavior apparatus. Mice are trained to hold a 10 s nose poke at a nose poke port in a gated chamber (width; 8 cm, length 14 cm, height 3 cm) at the start of a linear track (Width; 8 cm, length; 30 cm, height, 3 cm). Nose poke activity was detected by an infrared photointerrupter module positioned adjacent to the nose poke port exterior opening. After holding the nose poke for the required amount of time, the door opens (orange), allowing access to the reward zone at the end of the track. f) Long-duration nose poke learning curve. Each blue line indicates the performance of individual mice. Numbers at the end of each line indicate the number of mice represented by that terminus as several of the mice had overlapping performance levels at various points in the training procedure. g) Upper panel; Three examples of hippocampal time cells imaged during successful nose poke intervals. Traces show the relative fluorescence changes (ΔF/F %) across multiple 10s held poke trials for each cell. The color code plot at the bottom represents the averaged trace for each cell. Lower panel; Simultaneously imaged neurons from a single mouse (SST-Cre-9). Each row represents the normalized firing rate (5 ms bins) for one single neuron over the nose poke period averaged over all trials for each cell that met the criterion for time cells. Identified time cells were sorted by their peak firing time. h) Nose poke-based temporal discrimination behavior apparatus. Mice were trained to associate a 2.5 s held nose poke with a left or right turn (randomized per mouse), and a 10s poke with the opposite direction. The apparatus consists of a central nose poke port-equipped starting box (width; 8 cm, length 10 cm, height 3 cm) with two doors (orange) and two arms (width; 8 cm, length 50 cm, height 3 cm) on the left and the right. i) Learning curves for the nose poke-based temporal discrimination task in mice. Each line indicates the performance of 1 mouse; Three C57BL6J mice (B6–11, B6–12, B6–13), and Two SST-Cre transgenic mice (SST-Cre-6, SST-Cre-9). Dashed line indicates 70% threshold of statistical significance (Binomial test, P < 0.05). * indicates 70% or higher success rate on 2 consecutive days. j) Calcium imaging during the temporal discrimination task. Relative fluorescence change (ΔF/F %) for a total of 20 (out of 98 imaged) cells have been presented for successful trials associated with a 2.5 s nose poke (left panel, cells A-J) and a 10s nose poke (right panel, cells K-T). The trace activity data has been temporally aligned with movement tracking data showing the distance in cm of the animal’s head from the center point (nose poke port) of the I-maze. Vertical dashed lines delineate discrete periods of the trials