In vitro SPW-R activity recorded in the st. pyramidale of CA1 region of ventral hippocampal slices perfused with standard medium. A. Continuous long-lasting field recording of SPWs (trace on the top, low-pass filtered at 35 Hz) and the corresponding time histograms of amplitude (middle) and period (bottom). Data were obtained from a slice four hours after its placement on the recording chamber. Note the persistency and stability over time of both characteristics of SPWs. B. Record of spontaneous activity obtained from a different slice, presented at a faster sweep speed. C. A wide band record of a single SPW-R event (C1) and the filtered sweeps are shown, illustrating the distinct components of the event. Low-pass (0.5–30 Hz) and band-pass (100–300 Hz) filtering reveals the slow wave (C2) and the associated ripple oscillation (C3) respectively. Band-pass filtering at very high frequencies (0.5–1 kHz, C4) discloses the burst-like multiunit activity occurring mostly during the rising and peaking phases of the slow positive potential. D. FFT from 1 min raw record of spontaneous activity showing the difference in power between SPWs (upper diagram) and ripples (lower diagram, same power spectrum shown at a greater magnification). SPW dominant peak is at 5–10 Hz. Ripple activity is at ~150 Hz. E. Histogram of period (inter-event interval) of SPWs calculated from a population of slices, showing that most of the slices displayed a period between 0.2–0.6 sec, which correspond to a frequency range of 1.5–5.0 Hz. F. Auto-correlogram from a 5 min low-pass record from a distinct experiment, showing the typical degree of rhythmicity of SPWs.