Fig. 2: Spatial characterization of SPW-R-dSpikes in CA1 PV+ interneurons of awake mice.

a Example dendritic 3D Ca²⁺ responses from dendrite #1 shown in Fig. 1h at rest (control), during an SPW-R event (SPW-R), and during SPW-R independent putative backpropagating APs (bAPs). b Individual Ca²⁺ responses spatially averaged for the numbered dendritic regions indicated in a show a distance-dependent decrease and increase during putative bAPs and SPW-Rs, respectively. c Spatial distribution of the average dendritic 3D Ca²⁺ responses from dendrite #1 during putative bAPs and SPW-R-dSpikes (mean ± SEM, n = 4/5 bAPs/spikes). Black arrow indicates the spatial thresholds of the spike. Blue dashed line indicates linear fit to the proximal dendritic regions. Blue transients are overlaid with averaged 3D Ca²⁺ responses recorded in vitro and were induced by 5 APs. d Average SPW-R-dSpike-associated dendritic 3D Ca²⁺ responses as a function of distance from the soma (n = 11/5 cells/mice). Blue dashed line and black arrow indicate same as on panel c. Inset, pie chart denotes reliability of reactivation of the dendritic spike during successive SPW-Rs (75 spikes/ 287 SPW-R events/ 11 dendrites). The average length of the recorded dendrites was 314.2 ± 43.1 µm (mean ± SD). e Distribution of the spatial threshold of the SPW-R-dSpikes (n = 11/5/51 dendrite/mice/trace). f Red dashed boxes show the maximal intensity z projection of the imaged dendritic regions, with two different magnifications. Top, amplitude of individual SPW-R-associated 3D Ca²⁺ responses (gray traces) recorded along the white dashed curve from a dendritic segment of a PV+ neuron. Red trace is the average response (mean ± SEM). Bottom right, an exemplified individual SPW-R-associated 3D Ca²⁺ responses as a function of time and dendritic distance with the temporal integral of the response (gray line). Blue arrowheads indicate locations with local response maxima (hot spots). g Left, average SPW-R-associated 3D Ca²⁺ responses from hot spot regions and their histogram (blue line, mean ± SEM; n = 16). Right, average SPW-R-associated Ca²⁺ transients (mean ± SEM) from the central (blue) and lateral dendritic regions (red: centripetal, green: centrifugal) of hot spots. Panel e and g inset, box-and-whisker plots show the median, 25th and 75th percentiles, range of nonoutliers and outliers. Time delay for centrifugal vs. centripetal: p = 0.64; for centrifugal vs. central: p < 0.0001, paired t-test).