The analysis of Figures 7, 8 shows that voltage-dependent channels in sector II (but not sector I) cross the activation threshold, so that a local Ca spike is activated bringing about a remarkable KCa channels activation and a long pause. In sector II, Ca spikes and threshold crossing could be prevented by down-tuning the synaptic input. Indeed, when the number of pf synapses was increased progressively from 50 to 100, a sharp threshold in Ca spike activation was observed around 70–80 synapses. Interestingly, with sub-threshold responses the BPR of sector II became almost the same as for sector I (Figure 9).