Synaptic gating involves a variety of mechanisms by which the efficacy of neuronal activity is modulated. Additional studies demonstrate the permissive properties of synaptic gating. In certain instances, membrane depolarization will cause an opening of the gates that previously had an inhibitory effect on the neuron they were gating. This permissive gating is more than a matter of simple summation, however. Summation is the convergence of many EPSPs at the axon hillock (either from a single neuron firing at a high frequency or from many neurons firing at once) that depolarizes the membrane potential to the point of threshold. The membrane depolarization caused by the opening of synaptic gates causes an additional increase in intracellular calcium that facilitates the release of neurotransmitters; thus, it is able to selectively distribute information from the presynaptic cell.