FIG. 7.

Many inhibitory combination-sensitive interactions are not associated with low frequency–evoked hyperpolarization. A: delay curve shows strong spike suppression when the low-frequency sweep preceded the high-frequency sweep by 2–12 ms. Dashed line indicates criterion for combination-sensitive inhibition; values below the line exceed that criterion. B: PSTHs suggest that both LO and HI sweeps suppressed the response to the other sweep. C and D: averaged (n = 36) and individual voltage traces show no evidence of hyperpolarization to explain spike suppression. Resting membrane potential = −66 mV, spike height = 38 mV. See Fig. 2 for protocol.