Spatial distribution of the intraburst ISIs. A, Simultaneous extracellular field potential records of multiple unit activity were made in the stratum pyramidale of the CA3 and CA1 areas in a P16 hippocampal slice. Spontaneous burst-type discharges of individual neurons were extracted from continuous extracellular records. Rows of superimposed traces represent burst-type discharges of three individual neurons in the CA3a (top traces) and three individual neurons in the CA1 (bottom traces) pyramidal cell layer. Outlined areas indicate the range of timing for consecutive intraburst spikes. B, Histograms (top graph) represent spike timing in all detected burst-type discharges recorded from the CA3a (1105 spikes in 190 bursts) and CA1 (727 spikes in 200 bursts) pyramidal cell layer (bin size, 0.1 msec). Plot below shows significant differences of the corresponded intraburst interspike intervals: 4.9 ± 0.03 msec (1-2 ISI in CA3) and 5.4 ± 0.03 msec (1-2 ISI in CA1; p = 1.97 × 10^-21).