FIGURE 3.

Spike time response plot and phase response curve for an LTS cell. (A) Spikes (top, dotted line) evoked by a 1000-ms duration, 80-pA depolarizing current step (bottom) are perturbed by a 2-ms duration, 30-pA additional current step, indicated by the arrow. Action potentials in the unperturbed control are plotted as a solid line. (B) Phase shift of the postperturbed spikes depending on the perturbed phase. Stimulus 1 (perturbation at a late phase) induced phase advance (response 1), whereas stimulus 2 (at an early phase) produced phase delay (response 2). (C) Spike time response plot. The timing of perturbation is plotted by short bars. (D) A PRC is plotted using the same data shown in C. The average curve was fitted by a 7th-order polynomial curve (see Materials and Methods). The dotted curve shows the phase shift of the 2nd postperturbed spike with respect to the 1st spike after perturbation, and indicates a small 2nd-order effect on the interspike intervals immediately after perturbation.