FIGURE 4-22 Temporal Summation (A) Two depolarizing pulses stimulation (S₁ and S₂) separated in time produce two EPSPs similar in size. Pulses close together in time partly sum. Simultaneous EPSPs sum as one large EPSP. (B) Two hyperpolarizing pulses (S₁ and S₂) widely separated in time produce two IPSPs similar in size. Pulses coming fast partly sum. Simultaneous IPSPs sum as one large IPSP.