Fig. 3.

Dendritic Na⁺ spikes and NMDA spikes precede AP output. (A) Example recordings of local dendritic voltage at the location of dendritic Na⁺ spikes (red) and NMDA spikes (orange). Recording locations are shown on morphology (Left) with corresponding pipette colors. The intersection of voltage traces with the left vertical axis indicates distance from soma, while the scale bar shows the voltage scale. (B) Example snapshot of dendritic membrane potential as a function of space and time (same spatial and temporal extent as in A). Multiple dendritic Na⁺ spikes (initiation at red triangles; propagation indicated by white diamonds) and NMDA spikes (initiation at orange triangles) initiate and propagate across the dendritic tree. A bAP (blue triangle and white diamonds) occurs near time (t) = 54 ms. Contours are lines of equal membrane potential (maximum projection across all dendrites at this distance from the soma). (C) Distribution of the probability of initiating a dendritic Na⁺ spike (Top) or dendritic NMDA spike (Bottom) across the dendritic tree. (D) Spatiotemporal AP-triggered averages of dendritic Na⁺ spikes (Top) and NMDA spikes (Bottom), with BG dendritic spiking activity subtracted. Values in the red rectangles sum to the average numbers of dendritic events (shown in E) preceding a single AP. (E) Number of dendritic Na⁺ spikes (mean ± SD; red, Top) and NMDA spikes (mean ± SD; orange, Bottom) preceding a single AP compared to random time points (control, gray).