Figure 10.

Blocking inhibition can reduce spike directionality. a, Predicted membrane responses to control injection (excitation and inhibition) and with inhibition blocked (excitation only). With inhibition blocked, both the null and preferred PSPs exceed spike threshold (dashed line). Predicted PSPs in black, excitatory conductance in red, and inhibitory conductance in blue. Truncated spike shown in gray (top left). b, The model PSP peak amplitudes (peak − rest) normalized to spike threshold (dashed line). The control preferred PSPs (black filled) were very close to spike threshold, whereas the control null PSPs (black, open) were less than or equal to spike threshold. With inhibition blocked (red), both the preferred (filled) and null (open) PSPs exceeded spike threshold. In three sets, there was no asymmetry in the inhibitory magnitudes (large circles).