Figure 5.

Propagation of simple spikes into axon collaterals. A, Voltage-sensitive dye fluorescence image of a section of the axon arbor in recording position (top left). The spatial relationship with the soma is shown schematically on the right. Recordings from four locations indicated in the image are shown below. The bottom traces (black) indicate stimulus current and electrode recordings from the soma. Simple spikes evoked by trains of repetitive current pulses injected into the soma at 200–250 Hz reliably propagate in the main axon (green and blue traces), primary (red) collaterals, and secondary collaterals (orange). At 300–350 Hz, action potentials sometimes fail to initiate in one Purkinje cell (cell 1) but not in the other (cell 2). B, Probability of initiation of simple spikes in the main axon (blue, dashed line), as well as the probability of propagation of these spikes, once initiated, down the main axon (blue) and primary (green) and secondary (red) collaterals as a function of stimulation frequency (n = 6 neurons). During simple spike activity, all action potentials that were initiated propagated down the main axon and only rarely did these spikes fail to invade the primary and secondary axon collaterals. See supplemental Figure 3 (available at www.jneurosci.org as supplemental material). Error bars indicate SEM.