Figure 3.

Firing rate dependence on constant current. A. 1 s current pulses produce high frequency firing with relatively little spike frequency adaptation. After high frequency firing, there is a pause in spontaneous firing. B. Frequency-intensity relationship for the same cell shown in A. The mean firing rate vs current relationship for 1 s current pulses is sigmoidal in shape (blue) with a maximum sensitivity between 100 and 150 Hz firing rates. The rate defined by the first interspike interval in the response to the current pulse is shown in red. The deviation between this curve and the mean rate curve indicates that firing accelerated during the response. C. Instantaneous firing rate during the traces shown in A, showing the acceleration in firing at currents beyond 200 pA. D. Slow spike frequency adaptation in response to a much longer current pulse than used in A. After the initial acceleration, spike frequency very gradually decreases to a fraction of the initial rate. After cessation of the current pulse, spontaneous activity is silenced for about 20 seconds, and then gradually returns.