Figure 8. The shape of APs in distal segments of basal dendrites: voltage imaging.

A, 2 examples of voltage imaging performed at proximal and middle recording sites on basal dendrites (less than 180 μm from the cell body). Upper, AP-associated optical signal from basal dendrite (red, 135 μm from the soma) superimposed on the somatic optical record (black). Lower, same as above but different cell and different recording distance from the centre of the soma (180 μm). B, left, composite microphotograph of a layer V pyramidal neuron filled with JPW3028. Right, 3 examples of optical signals sampled from distal dendritic segments at distances larger than 180 μm, as indicated in the left panel. There is no apparent broadening of the backpropagating AP. Note that ROI ‘3’ is ∼150 μm beyond the branch point. C, example of an experiment in which the half-width of the AP increases in distal dendritic segments. Each trace in Fig. 8 is the product of temporal (4 sweeps) and spatial averaging (6–9 pixels). All somatic signals are coloured black and dendritic recordings are coloured red. The distance from the centre of the soma is indicated above each dendritic recording.