Extended Data Fig. 1: Calcium imaging in the anterodorsal thalamic nucleus (ADN) and identification of HD neurons.

a. Histology data showing coronal brain sections from each mouse with GCaMP6f expression, in ADN (anterior part). Mouse ID written in the top right and scale-bars shown in the bottom left of each panel. In total, 12 mice were injected and implanted for this study, only 3 (shown here) provided enough simultaneously recorded head-direction cells for continued experimentation. b. Directional maps of ADN in each mouse. HD cells are coloured by their preferred firing direction (PFD). Colour-wheel shows angle-colour assignments. Mouse ID written on the top right and scale-bars shown in the bottom left of each panel. c. Examples of HD cells’ coverage of the azimuthal plane, in each mouse. Rows in each matrix represent tuning curve heatmaps of individual HD cells. The amplitudes of individual tuning curves are normalized. Mouse ID written above each panel. d. Left: An example polar tuning curve for a HD neuron. Yellow line: direction of maximum firing activity (that is, PFD). Firing activity is occupancy normalized. Right: Top-row: Example calcium signal deltaF/F (green) from one HD neuron and deconvolved trace (red). Both traces were normalized. Middle-row: Measured HD. Bottom-row: Extracted stimulus signal of the HD neuron’s PFD. Peaks indicate instances of the animal facing the particular PFD. The deconvolved signal is cross-correlated with the stimulus signal in order to obtain the Pearson’s correlation coefficient which reflects the cell’s degree of HD tuning (r = 0.85 in the case of the current example). e. Distributions of correlation coefficients after 1000 circular-shift shuffles of the firing activity signals (smoothed deconvolved traces) of all HD neurons, in each mouse. Red and green vertical lines indicate 95^th and 99^th percentiles, respectively. Data includes 10 baseline recordings of 3 min each, for every mouse. Of all recorded cells, ~94% met the 95^th percentile selection criterion while ~83% met the 99^th percentile selection criterion.