The NMDAR contribution to subthreshold EPSP summation is significantly stronger in PFC pyramidal cells than in FS neurons. A, Left, Example of average eEPSPs evoked by repetitive stimulation (5 stimuli, 20 Hz) in a pyramidal cell recorded at approximately −80 mV (black trace) and at a depolarized membrane potential near threshold (gray trace). Right, Bar graph summarizing the differences in eEPSP summation at different membrane potentials in the absence or presence of the NMDAR antagonist d,l-AP5 (100 μm). *p < 0.02 (eEPSP₅/eEPSP₁ ratio, hyperpolarized: 1.82 ± 0.21, depolarized: 3.41 ± 0.62, n = 14, Z = 2.113 p < 0.05, Mann–Whitney U test; eEPSP₅/eEPSP₁ ratio hyperpolarized+AP5: 2.03 ± 0.46, depolarized+AP5: 2.65 ± 0.37, n = 12, Z = 1.386 p = 0.165, Mann–Whitney U test). The depolarized membrane potential in control and AP5 conditions did not differ significantly (control: −59.5 ± 2.7 mV; AP5: −57.4 ± 3.0 mV, p = 0.619). B, Left, Example of average eEPSPs evoked by repetitive stimulation of excitatory inputs (5 stimuli, 50 Hz) onto a FS cell recorded at approximately −80 mV (black traces) and at a depolarized membrane potential near threshold (gray traces). Right, Bar graph summarizing the differences in eEPSP summation at different membrane potentials in the absence or presence of the NMDAR antagonist d,l-AP5 (100 μm) (eEPSP₅/eEPSP₁ ratio, hyperpolarized: 1.33 ± 0.23 n = 11, depolarized: 1.59 ± 0.39 n = 10, Z: 0.281, p = 0.778, Mann–Whitney U test; eEPSP₅/eEPSP₁ ratio hyperpolarized+AP5: 1.24 ± 0.20 n = 9, depolarized+AP5: 1.46 ± 0.45, n = 7, Z = 0.0532, p = 0.958, Mann–Whitney U test). The depolarized membrane potential in control and AP5 conditions did not differ significantly (control: −55.9 ± 1.9 mV; AP5: −55.0 ± 2.9 mV, p = 0.791).