Figure 2. Quantification IEDs related extracellular potentials and analysis of IED origin and propagation. A, Example of interictal epileptiform discharge in hippocampal-entorhinal cortex slice of a P19 rat. Extracellular field potential recording (wide band, 0.1 Hz to 4 kHz) at the CA3 pyramidal cell layer before filtering (left trace) and after filtering (right traces) for EEG components of IED (1-100 Hz bandpass filter) and IED-related fast field ripple (200-500 Hz bandpass filter). EEG components are labeled (I, primary population spike; II, slow spike wave). B, Simultaneous extracellular field potential records in the pyramidal cell layer of the CA3a, CA3b, CA3c, CA1, and granular cell layer (G. C.) of the dentate gyrus regions. Examples of IEDs before (left traces) and after (right traces) filtering in EEG band (raw data, 0.1 Hz to 4 kHz; EEG, 1-100 Hz). EEG components are labeled (I, primary population spike; II, slow spike wave; III, secondary afterdischarges). Shift of the negative peaks of primary (initial) population spike (Δτ) shows that the population spike is initiated in CA3a and bidirectionally propagates to CA3c dentate gyrus and CA1. C, Simultaneous extracellular records in the CA3a stratum oriens, stratum pyramidale, stratum radiatum, and stratum lacunosum-moleculare layers (wide band range, 0.1 Hz to 4 kHz). Filtered traces (1-100 Hz) show that the population spike is initiated in the somatic layer and propagated into dendritic trees and axons. A-C, IEDs induced by 8.5 mm [K+]o.