Fig. 7.

Differential filtering of backpropagating APs in the apical tuft. (a1) Pyramidal cells in this experimental group ($n=107$) with signal (YES) or without $\mathrm{AP}\text{-}{\mathrm{Ca}}^{2+}$ signal detected in apical tuft branches (NO signal). (a2) Apical tuft branches ($N=325$) are divided based on the number of AP peaks detected (0 to 3). (b1) L5 pyramidal neuron. (b2) Blowup of the area marked by the rectangle in (b1). (b3) Simultaneous recordings of $\mathrm{AP}\text{-}{\mathrm{Ca}}^{2+}$ signals from three sister branches (ROI 1 to 3) are aligned with the whole-cell recording (ROI 0). (b4) Signals from two branches (ROI 1 and ROI 2) are scaled based on the first AP. Rectangle marks notably different calcium events. (c1) Apical tuft of a L5 pyramidal neuron with three ROIs selected. (c2) One apical tuft branch experiences two APs (ROI 1), while at the same moment of time, other branches experience three APs (ROI 2 and 3). (d1) Apical tuft of a L5 pyramidal neuron with seven ROIs. (d2) Individual branches experience 3, 2, or just 1 AP, depending on the number of branch points (BP) separating them from the main apical trunk. (e1) Apical tuft (AF594 channel) captured by the video microscopy camera. (e2) The same apical tuft (OGB1 channel) captured by the Ca-imaging camera. (e3) Two AP peaks are lost as APs backpropagate through the branch point (BP, arrow)—compare signals before BP (ROI a3) and after propagation through BP (ROI a4). Signals are scaled based on the first AP. (e4) Same data as in (e3), except signal amplitudes are expressed as $\mathrm{\Delta }F/F$.