Single-epoch neuromagnetic signals during epileptiform activities in guinea pig longitudinal CA3 slices

Neuromagnetic fields with high signal-to-noise ratios can be measured above longitudinal CA3 slices of the guinea pig during single epochs of interictal- and ictal-like synchronized population activities. Technical refinements enabled us to reduce the number of epochs for clear responses from over 5000 needed in an earlier study to single epochs. Simultaneous recording of field potentials revealed that neuromagnetic fields reflect intracellular currents in the pyramidal cells. Intracellular currents could be estimated from the external magnetic fields during paroxysmal depolarization shifts, multiple bursts, and slowly varying potential shifts lasting several seconds.