Extended Data Fig. 6: High and low rate CA1 principal cells are skewed towards deep and superficial pyramidal sublayers, respectively.

a-d, For each CPP task day, we estimated the position (depth) of individual tetrode-recorded principal cell soma by leveraging silicon probe recordings with known spacing between the recording sites along a linear shank (25-μm steps). From these silicon probe recordings, we first computed the laminar profile of sharp-wave/ripples (SWRs) detected in the local field potentials (LFPs) along the radial axis of the dCA1 hippocampus (a). We used the peak of the corresponding depth profile of the ripple-band (110-250Hz) power to estimate the centre (middle) of the pyramidal (pyr.) layer (b; red cross). Using the average LFP waveform of the SWR events detected in these silicone probe recordings, we then established a SWR template where we reported the distance relative to the estimated centre of the pyramidal layer, knowing the precise distance between the recording sites on the linear shank (c). Next, we computed the individual SWR profile of each tetrode for CPP recording days finishing with a sleep session, this way estimating the depth of each individual tetrode (and thus that of the somas of its recorded neurons) by positioning its SWR profile within the silicone probe SWR template (the ground-truth vertical depth; c). Shown in (d) are examples of single-tetrode SWR profiles and their estimated depth. (e) Left: the estimated depth of principal cells as a function of the average firing rate measured in the CPP task. Each data point represents one principal cell. Right: the same data plotted as a firing rate probability distribution per estimated depth. f, Same data as in (e) but plotted as a ridge plot to better visualise the relation between firing rate of principal cells and depth of their recording tetrodes. Note that principal cells in the deep sublayer of the dCA1 pyramidal layer (closer to stratum oriens) show higher firing rates than those in the superficial sublayer (closer to stratum radiatum) (line of best fit: y=23.34log(x)-74.7; p=10⁻³⁰; two-sided Wald Test). g,h, The same analyses shown in (e,f) but performed for the bursting index. Note that principal cells of the deep dCA1 sublayer show higher spike bursting compared to those of the superficial sublayer (line of best fit: y=47.43log(x)-15.0; p=10^-64; two-sided Wald Test). (i) Relative prevalence (left) and cumulative distribution (right) of low (blue) and high (red) rate principal cells along the dCA1 radial axis. Low and high activity cells are skewed towards superficial and deep dCA1 pyramidal sublayers, respectively (p=0.016, Kolmogorov-Smirnov 2-sample test).