The Spikelets of Complex Spikes Fail to Propagate
Figure 8. Action potentials show variable propagation probabilities during complex spikes. A. Voltage-sensitive dye fluorescence image of the soma-axon region in recording position shown on the left. Top trace on the right (black): timing of climbing fiber activation by extracellular electrical stimulation. Second trace (black): whole cell somatic recording. Lower color traces: optical recordings of AP signals, evoked with climbing fiber stimulation, from 12 locations indicated on the image. Each trace is a temporal average of 18 trials and a spatial average of 6-8 pixels. Signals are scaled so that the 1st AP is of the same height. B and C. Action potential onset latency, measured from the time to half-maximum amplitude, as a function of distance from the edge of the soma for the first sodium spike (thin trace) and subsequent spikelets (red and blue traces) for a Purkinje cell (B) and average group data (C). In both cases the first spikelet fails to propagate at 30-60 mm, prior to the 1st branch point.