Fig. 6.

Dependence of the response properties of a simulated spiking neuron on the amplitude of the deterministic membrane potential component. The deterministic component scaled with a factor of 1 corresponds to the unaltered membrane potential fluctuations of a tangential cell to dynamic motion stimulation averaged across 100 trials. It lasted for 2960 msec. A membrane potential of 0 mV corresponds to the resting potential of the tangential cell. The amplitude of the deterministic membrane potential component was increased and decreased by 50% (see insets). The stochastic membrane potential component was fitted to the experimental data (see Materials and Methods). The mean spike count and the spike count variance were determined across 500 individual response traces for each input condition. A, Dependence of the spike count on the deterministic membrane potential component for simulated and experimentally determined data (see inset). Note that different symbols superimpose. The mean deterministic component and the mean spike count were determined in 20 msec time windows. The mean deterministic membrane potential was assigned to activity classes with a width of 2 mV. Spike counts were averaged if the corresponding mean membrane potential fell into the same activity class. For the experimental data, 100 responses from an H1 neuron were evaluated. The neuron was stimulated with the same dynamic motion fluctuations as the HS cell used to determine the deterministic response component of the membrane potential. In another recording (data not shown), the mean spike count for each activity class of the membrane potential was slightly larger than that of the model cell. B, Spike count variance as a function of the mean spike count within 20 msec time windows. As for the experimental data (see Materials and Methods), the mean spike count was assigned to activity classes with a width of 0.4 spikes per time window. Spike count variances were averaged if the corresponding mean spike count fell into the same activity class. C, Spike count variance as a function of the mean spike count within 100 msec time windows. Consecutive time windows overlapped by 90 msec. The mean spike count was assigned to activity classes with a width of two spikes per time window. Spike count variances were averaged if the corresponding mean spike count fell into the same activity class.