Figure 3.
Summation of EPSPs with steady-state voltage changes varies with synapse location. (A and B) Steady-state changes in membrane potential were produced by somatic current injection. Perforant path and mossy fiber EPSPs were elicited at a variety of membrane potentials. Lines represent best linear fit through these data points. The amplitude of perforant path EPSPs (A and C) did not decrease with somatic depolarization, indicating linear summation of perforant path EPSPs with steady-state changes in Vm. (B and C) In contrast, mossy fiber EPSP amplitude was reduced by depolarization consistent with the reversal potential of AMPA receptor-mediated EPSPs. (D) The linearity of summation also showed voltage dependence, with summation becoming linear with depolarization.