Fig. 1

Sparse orthogonal population representation of spatial location in the retrosplenial cortex. a Head-fixed locomotion assay. Mice moved a 150-cm linear treadmill (top) with tactile cues on its surface (bottom). A drop of sucrose water (blue) was delivered at a fixed location for every completed lap. b Lap running behaviour. Movement speed as a function of location for 53 consecutive laps from one experimental session. The animal moved robustly and slowed down or paused most frequently near the reward (as shown by dark colours on the left). c Cellular imaging of neural activity in the retrosplenial cortex (RSC) during head-fixed treadmill running. (top) Illustration of superficial and deep RSC neurons labelled with calcium indicator GCaMP6m (green dots). Calcium imaging was performed with a two-photon microscope through a glass window. (bottom) Tangential view of the labelled superficial RSC neurons with an example imaging field of view (black square). Red lines indicate superior sagittal sinus and transverse sinuses. Scale bar, 1 mm. A: anterior; L: lateral. d Calcium fluorescence signals (top, red) and inferred neural activity (top, black) of six example superficial agranular RSC neurons showing place cell activity; speed and treadmill position are at the bottom. Neural activity was inferred using a fast non-negative deconvolution algorithm 64. e Normalized activity of the six RSC place cells in d as a function of location for multiple laps. The y axis in each colour map corresponds to trial number. Note how neurons were activated as the animal crossed specific locations. Activity was normalized to the time spent at individual locations. f Raster plot showing activation time points for 31 simultaneously imaged RSC place cells, for the same session as in e, together with position (top). Activation time points defined as time points of peak response in each lap for each neuron. Cells ordered by the location that evoked largest responses. Note the repeated sequences of activation during movement and lack of activation when the animal was not moving. g Average normalized activity as a function of location for the 31 RSC place cells shown in f. h Correlation matrix (Pearson correlation coefficient) of population vectors as a function of position for data shown in g. i Correlation matrix (Pearson correlation coefficient) of population vectors as a function of position for data from four mice. (Data from WT mice with AAV1-hSyn-GCaMP6m injections.)