Depolarization increases the correlation between a complex waveform and neuronal discharge. A, Current waveform, derived from an intracellular in vivo recording (Nowak et al., 1997), that was injected with varying levels of depolarization. The vertical dashed lines are visual guides to help align peaks in activity and the injected current. The histogram illustrates the response of the neuron at a membrane potential of -83 mV. B, Depolarization of the resting membrane potential of the cell to -76 mV with the intracellular injection of current results in a marked enhancement of neuronal responsiveness to the injected waveform. C, Group data (6 cells) demonstrating that depolarization results in an enhancement of the peak cross-correlation between the amplitude of the input and the neuronal firing rate.