Figure 4. Suppression of spontaneous bursting after SK Block prevents loss of responses to weak depolarizing input events applied with dynamic clamping.

A: Spontaneous activity of a CN neuron before (black) and after superfusion of 100 nM apamin (red). A portion of the apamin spike pattern is superposed on the control spike train at the matching time scale to allow a direct comparison of spikes (red overlay demarcated by box). This burst suppressed (BS) neuron was voltage-clamped to a holding potential of −60 mV to prevent spontaneous high frequency bursting. The neuron was released from voltage clamp only during the time of dynamic clamp stimulus application. B: Stimulus aligned voltage responses of a BS neuron to a synaptic conductance input pattern applied via dynamic current clamp on the left before (black) and after apamin (red) presentation. Raster plots are shown in the center and E_syn is depicted in green. BS neuron responses to weak depolarizing events were almost never reduced, unlike that seen for FB neurons (Fig. 2B), but fast frequency burst responses were still only associated with large depolarizing events. On the right is an expanded inset of the boxed area. C: ISI histograms of the same BS neuron responses to dynamic clamp-applied synaptic input. The increase in responses to both large and small depolarizing events lead only to an increase in the shorter ISIs. Both the SR (10.6 Hz to 14.4 Hz) and ISI-CV (0.422 to 0.687) of the BS neuron depicted in (B) increase after apamin presentation. D: The data from all 7 BS neurons show a maintained spike time precision during in responses to dynamic clamp stimuli, but a significant increase in ISI-CV (paired t-test, p < 0.001) and a non-significant increase in SR (paired t-test, p = 0.1).