Effects of thiopental on Ripple oscillation. A. Examples of ripple oscillation (filtered traces) from three slices (a-c) illustrating the concentration-dependent reversible reduction in number of ripples and duration of ripple episode by thiopental. Note that even at 100 μM of the drug, which strongly suppressed the amount of ripples, the oscillation frequency remained unchanged. B. Power spectra from three experiments (a-c) showing the reduction of ripple power at 50 and 100 μM but not at lower concentrations. C. Plots of collective data of drug effects (percent changes) on the various measures of ripple oscillation. Asterisks mark the lowest concentration with statistically significant drug action (see text for details of statistical analysis). Note that ripple number and ripple episode duration were more sensitive than ripple power and ripple amplitude. Measures of number, duration and amplitude for each of the five drug concentrations (10, 25, 50, 100 and 200 μM) were respectively collected from 10, 12, 17, 10 and 8 slices. The corresponding numbers of slices for ripple power measures were respectively 12, 14, 22, 15, and 9. D. Recordings of ripples (upper traces) and multiunits (middle traces), revealed after filtering original records, showing the thiopental-induced reduction in the rate of multiunits during ripple episodes. Dotted line indicates the threshold level set in this experiment for spike detection. Histograms of multiunit rate (bottom panel) triggered by peaks of SPWs (not shown) used to measure the mean rate under the different experimental conditions.