Fig. 1: Illustration of the recording conditions for hippocampal interneuron activity in head-fixed mice navigating through virtual environments.

a Schematic of the recording setup. b Virtual circular tracks and behavioral layout. Familiar and novel tracks are characterized by different wall and floor patterns. c Schematic of the implantation. The lateral window implantation for CA2/3 recordings (Methods) is depicted with dashed lines. d Illustrative, time-averaged GCaMP6f (white) and mRuby2 (red) fluorescence of CA1 PV-cells in vivo, representative for the recording conditions in n = 12 experiments. e Fluorescence signal (black), animal running speed (blue) and position on the circular track (red) of an illustrative example CA1 PV-interneuron (IN) over time. f Calcium activity of a PV-IN (n = 1, same as in d) as a function of running speed. Dots with lines represent mean ± SEM; dotted blue lines represent linear fit to the data with an offset. g Activity (color-coded) of the same IN as in e, f as a function of position on the familiar circular track over multiple trials, consisting of 60 s running on the respective tracks. h–k Same as in d–g, but for an example SOM-IN (n = 1) in the DG. Image in h is representative for n = 8 experiments. For cell examples from all recorded areas, see Supplementary Fig. 1d–i.