Fig. 1: Activation of long dendritic segments revealed by fast 3D imaging in SPW-R-associated PV+ cells in behaving mice.

a Schematic of the combined LFP recording, fast raster scanning, and 3D dendritic measurements with AO microscopy (g) during SPW-Rs in the periods of water licking. Inset, representative raw and filtered local hippocampal LFP signals with an SPW-R event from the stratum pyramidale from the ipsilateral hippocampus. Bottom panel indicates the position of the local hippocampal (loc. HC), reference (ref.) and contralateral cortical (cl. ECoG.). b Red and white dashed circles indicate PV+ neurons in the CA1 region of the hippocampus, which were active and inactive, respectively, during SPW-Rs. c Local LFP signal and somatic Ca²⁺ responses recorded simultaneously to b. Arrowheads indicate SPW-R events. Red traces indicate SPW-R-associated somatic responses. d Left raw, enlarged view of the SPW-R (#1a) event indicated with filled arrowhead in c is shown with and without filtering with corresponding somatic responses. Right raw, same as left raw, but with another event (#1b). e Individual SPW-R-associated Ca²⁺ transients from cell #1 overlaid with the average (mean ± SEM). f Ratio of the active PV+ neurons, which showed SPW-R-correlated Ca²⁺ responses. g–j Non-uniform (global and local) dendritic activation revealed by fast 3D-AO imaging in a sample SPW-R-correlated PV+ cell under in vivo conditions. g Dendritic arbor of the SPW-R-correlated cell in the stratum oriens. Red and yellow ribbons indicate dendritic segments selected for fast 3D ribbon scanning. The total length of the selected and simultaneously recorded dendritic segments was 1568 µm. h Fluorescence was recorded simultaneously along the 10 dendritic regions shown in g and then projected into 2D as a function of distance along the longitudinal and transverse directions of the 3D ribbons (Supplementary Movie 1). Inset indicates ratio of recorded dendrites with SPW-R-correlated activity (n = 11/5, cells/mice). i Left, example 3D Ca²⁺ response during SPW-R events from the numbered dendrites shown in h. Right, average dendritic responses from the same ten dendrites. Black arrowheads indicate two SPW-R events. j Similar to panel i but during putative backpropagating action potentials. Empty arrowheads denote putative backpropagating action potentials.