Figure 4.

Axonal illumination reliably elicits action potentials. A, Experimental configuration. Whole-cell current clamp recordings were made from CA3 hippocampal pyramidal cells with ChR2-Venus expression driven by AAV1-ChR2. Cells were stimulated optically with light focused either over the cell soma or ∼500 μm away over the stratum radiatum. B, Less light was required to generate action potentials when the cell soma was illuminated (n = 21), but illumination over axons produced action potentials in all cells at the brightest intensities (n = 11). C, Representative spikes evoked by pairs of flashes delivered at 10–200 ms intervals. D, At the brightest laser intensity, the second flash generated a spike for all ISIs except 10 ms (n = 13). E, Representative spike train elicited by flashes delivered at 50 Hz. Same scale as in C. F, Average number of spikes elicited by 10 flashes at frequencies from 10 to 100 Hz (n = 7). Data are expressed as average ± SEM.