Figure 7.

Effect of desensitization on threshold for direct activation. A. Illustration of the stimulus with a 16Hz pulse train of 1ms (black) superimposed with four short-duration pulses (200μsec) (gray) that elicit spikes through direct activation. B. Example of spiking response to 16Hz pulse train of 1ms, giving an initial burst of spikes and quickly desensitizing to give no response by the fourth pulse. C. Example of the response to the stimulus illustrated in A, where the desensitizing pulse train of 16Hz was presented for over 8sec before the onset of the short duration pulses. The stimulus artifacts of the 16Hz pulses (asterisks) and the short duration pulses (arrows) can be seen. D. Zooming in on the gray box in C, a spike is elicited by direct activation for 65μA input current, but not for 63μA. E. The effect of the desensitizing pulse train on the threshold for direct activation is shown (n=4).