Figure 1.

Precision of onset latency measurement. A, Examples of AP light responses with different onset latencies generated by driving a light-emitting diode with an AP voltage command within its linear range and detected with either a photodiode (PD) sampling at 100 kHz (top) or our camera-based system sampling at 10 kHz (middle). Bottom, Plot of onset latency of AP light responses detected with the PD versus the camera system. B, Image of a layer 5 pyramidal neuron filled with voltage-sensitive dye (resolution, 80 × 12; depixelated). ROIs at the soma, apical dendrite, and axon are indicated. C, Example of an AP evoked by extracellular stimulation and recorded at the soma via the whole-cell recording pipette (top; timing of extracellular stimulus indicated by stimulus artifact) together with the associated VSD signals at the soma for a single sweep (middle) and an average of 60 trails aligned individually to the soma AP (bottom). The scaled voltage recorded at the soma is shown in orange. The somatic ROI is indicated in B. D, Average AP evoked VSD signals (100 trials) in the axon, soma, and apical dendrite for the ROIs indicated in B. The linear regression fitted to the rising phase of the different VSD signals used to determine onset latency at 50% of peak is superimposed (black).