Figure 1: Experimental set-up.

(A) Schematic showing a mouse’s head equipped with a head plate and the LFP recording CA1 electrode. The location of the imaging area is indicated (red). Scale bar represents 10 mm. (B) Schematic showed a head-fixed mouse on the experimental device. The objective on top of the mouse’s head was used for calcium imaging. (C) Design of the optical encoder electronic circuit with three output BNC channels labelled as channel I (black), channel A (red), and channel B (blue), component maps for the optical encoder and power plug connector, power plug circuit, pull-up resistances, and output BNC. (D) Representative traces from the three channels when the mouse exhibited spontaneous behaviour. Channel I (black) indicates a full wheel rotation (one turn = 24.19 cm) between two 5-V inflections. Channels A (red) and B (blue) indicate fringes (each square signal is equal to 1/500 of a turn). Note that these channels were phase-shifted to monitor the direction of the wheel’s rotation. The corresponding instantaneous speed trace (black) and underlying behaviour phases are shown (bottom). The mobility threshold (grey line, 2 cm s⁻¹) was used to distinguish run epochs (red bars) from flickering (green bars) and immobility (cyan bars) periods. Grey outline box (*) indicates the zoomed view (right panel, 500-ms duration). (E) Scatter plot showing the speed measurements obtained after processing the data from channels (A and B) using the algorithm (see Methods), and the speed imposed by the wheel rotation engine (black dots, Pearson’s correlation coefficient: r = 0.99, p < 0.0001). It should be noted that the linear relationship is shown for the full tested range (0 to 120 cm s⁻¹). The insert indicates the real mouse speed (red dots) obtained from the median speed for each turn (from the channel I calculation, see Methods).