Simultaneous intracellular and field potential recordings in the CA1 region of the Has3^−/− hippocampus. A–C, Tracings illustrate the range of excitatory activity seen in CA1 stratum pyramidale neurons coincident with the spontaneous field potentials in brain slices from Has3^−/− mice. Top tracing is intracellular recording from the Has3^−/− CA1 stratum pyramidale, and bottom tracing is simultaneous field potential recording with extracellular electrode placed at the border of CA1 stratum radiatum and stratum lacunosum-moleculare. Asterisk indicates the event that is expanded in the right column. A, This neuron showed interictal-like epileptiform events coincident with the rhythmic field potentials. Input resistance 23 MΩ, resting potential −70 mV. B, This neuron showed a small depolarization and single action potential coincident with each of the rhythmic field potentials. Input resistance 23 MΩ, resting potential −65 mV. C, This neuron showed only a tiny depolarization or no apparent membrane potential change coincident with each of the small rhythmic field potentials (arrows). However, ictal-like bursting occurred in the cell coincident with infrequent, larger, ictal-like field potentials. Right side of the figure shows that the ictal-like field potential began before this cell began to fire, but that the later individual peaks in the field potential correspond to depolarizations and action potentials in the cell. Input resistance 16 MΩ, resting potential −55 mV. Results presented in A–C are from three different slices.