Fig. 4: Supralinear dendritic Ca²⁺ signal integration during in vivo SPW-R-doublets.

a Non-linear summation of the 3D Ca²⁺ responses during SPW-R doublets were calculated using two different approaches in a distal dendritic segment of a PV+ neuron (above the spatial threshold in the range of 134-300 µm from the soma). Left column, green and blue transients are average dendritic Ca²⁺ responses from the high-ripple group. The blue transient was shifted with the average time interval of doublets. Red and black transients are the average response recorded during SPW-R doublets and the mathematical sum, respectively. Bottom, the overlaid average transients indicate strong supralinear integration. Right column, the same calculation, but the second transient (blue) was replaced by the average response from the low-ripple group because the second event of the doublets statistically belongs to the low-ripple group (Figs. 3d and 4i). b–e Somato-dendritic distribution (0–285 µm) of SPW-R-associated dendritic activity along the somato-dendritic axis during low-ripple (blue), high-ripple (green), and the first (pink) and second (red) peaks of doublets in an example PV+ interneuron (n = 18/12/6 high ripples/low ripples/doublets). b Distribution of individual SPW-R-coupled Ca²⁺ transients. Data were recorded at submicron resolution using 3D ribbon scanning to precisely follow thin dendritic segments and then binned into 25 µm intervals. In contrast to low-ripple-associated responses, high-ripple- and doublet-associated Ca²⁺ transients increased as a function of distance from the soma. c Box-and-whisker plots of the amplitude of the transients showing the coactivation at the somatic (0 µm) compartment. d The same but for proximal dendritic segments (<20 µm), e The same but for distal (>150 µm) dendritic segments (Student’s unpaired t-test; *p < 0.05, **p < 0.01, ***p < 0.001). f–h, Box-and-whisker plots of the amplitude of SPW-R-coupled Ca²⁺ transients from all PV+ cells in the somatic, proximal and distal dendritic regions (n = 5 PV+ cells, n = 33 somato-dendritic segments, n = 51 SPW-R-dSpikes, n = 409 somato-dendritic segment-related SPW-R-Ca²⁺ events). The mathematical sum of two high-ripple-associated responses (math. Σ high), and one low- plus one high-ripple-associated response (math. Σ low) were calculated with 100 ms delay between the events of doublets. i Box-and-whisker plots of the power of the simultaneously recorded SPW-R events (n = 5 cells/mice). j Temporal dependence of the amplitude of summation during doublets.